theoretical and experimental challenges
TRANSCRIPT
QED in laser-plasma interactionstheoretical and experimental challenges
Tom BlackburnChalmers University of Technology
4th July 2017Workshop on Plasma Astrophysics From the Laboratory to the Thermal Universe
Introduction
Goals
Understanding QED in laser-plasmas is necessary
Understanding QED in laser-plasmas is interesting
(Understanding QED in laser-plasmas is difficult)
Introduction
Goals
Understanding QED in laser-plasmas is necessary
Understanding QED in laser-plasmas is interesting
(Understanding QED in laser-plasmas is difficult)
Introduction
Goals
Understanding QED in laser-plasmas is necessary
Understanding QED in laser-plasmas is interesting
(Understanding QED in laser-plasmas is difficult)
Introduction
Quantum electrodynamics
Fundamental theory of the interaction between light and matter
Unifies quantum mechanics with special relativity
Charged particles interact via the emission and absorption of photons
Introduction
Quantum electrodynamics
Fundamental theory of the interaction between light and matter
Unifies quantum mechanics with special relativity
Charged particles interact via the emission and absorption of photons
Introduction
Quantum electrodynamics
Each vertex carries a factor of e the electron charge and a δ-function encoding the conservation of momentum
Simplest two photon emission (radiation reaction) and pair creation
Introduction
Quantum electrodynamics
Two-photon pair creation (Breit-Wheeler process) not observed experimentally (heavy ion collisions hohlraums)
Multiphoton Breit-Wheeler seen at SLAC (50 GeV electron beam into 1018 Wcm-2 laser 140 positrons) Non-linear index n = 5 6
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Reduce a hard problemby splitting it into a ldquoeasyrdquo part and a ldquosmallrdquo correction
Results take the form of a series expansion around the easy (ie unperturbed) solution
eg ground state energies in quantum mechanics
Beyond perturbative QED
Perturbation theory in quantum mechanics
Reduce a hard problemby splitting it into a ldquoeasyrdquo part and a ldquosmallrdquo correction
Results take the form of a series expansion around the easy (ie unperturbed) solution
eg ground state energies in quantum mechanics
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Zeeman effect Coulomb potential perturbed by static magnetic field
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
More = better
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
More = better
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
More = better
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
More = better
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
But the series diverges
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
But the series diverges
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory generically leads to divergent series
This has been known for a long time ndash see Bender and Wu Phys Rev 184 1231 (1969)
Besides infinities are interesting
Beyond perturbative QED
Perturbation theory in quantum mechanics
ldquoThe series is divergent therefore we may be able to do something with itrdquo - O Heaviside
ldquoThis is infinity here It could be infinity We donrsquot really donrsquot know But it could be It has to be something ndash but it could be infinity rightrdquo- D J Trump
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Use the integral definition of a factorial
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Use the integral definition of a factorial
Swap the summation and integration
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
If they dont the integrand has a pole on the real axis
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
If they dont the integrand has a pole on the real axis
This has physicalsignificance
Beyond perturbative QED
Perturbation theory in quantum mechanics
Recall the dispersion relation for an EM wave in a warm plasma
The permittivity has a pole where the phase velocity of the wave and the particle velocity are equal
Gives rise to Landau damping
This has physicalsignificance
Beyond perturbative QED
Perturbation theory in quantum mechanics
If the terms do not alternate in sign Borel summation gives you an imaginary term that is non-perturbative in the coupling strength
Non-perturbative in the sense that exp(-1x) has Taylor expansion about 0 that is 0 to all orders
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Divergent perturbative series with coefficients that do not alternate in sign
Zeeman effect Coulomb potential perturbed by static magnetic field
Divergent perturbative series with coefficients alternating in sign
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Ionization rate
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative Why perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Does the same occur in quantum field theory
After all perturbation theory has proved extraordinarily successful
Beyond perturbative QED
Perturbation theory in quantum mechanics
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
S has a non-perturbative imaginary part
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
The action for a static electric field acquires an imaginary part that is non-perturbative in the electric field strength
Stark effect = ionisation rate Here we get the pair-creation rate from the vacuum
Ecrit = 13times1018 Vm
Beyond perturbative QED
Perturbation theory in QED
How do we access fields of this magnitude in the lab
Important parameter is χ (ratio of electric field in electron rest frame to the critical field of QED)
Beyond perturbative QED
QED in intense fields
χ = 1 means the electron sees in its rest frame a field strong enough for non-perturbative effects to dominate
Low order terms are suppressed only high order terms (ie involving large numbers of background photons) contribute
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
What about arbitrary field structures
Beyond perturbative QED
QED in intense fields
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
What do we lose by doing this
Harmonics sub-harmonics interference resonanceshellip
When is it acceptable to do so
How much bigger than 1 must a0 be
Coupling sfQED and classical processes
Locally constant field approximation
Other constraints on PIC simulations
Size of timestep must be set to avoid multiple scatterings (constraint set by rate of photon emission is strongest)
C P Ridgers et al J Comp Phys 260 273 (2014)
The rates (not cross-sections) for photon and pair production are calculated in an equivalent system of fields with the same instantaneous value of χ
eg a static magnetic field in the ultrarelativistic limit T Erber Rev Mod Phys 38 626 (1966)
Coupling sfQED and classical processes
PIC + Monte Carlo
We assumed a classical background field
Contains sufficient energy that the field is not affected by a (single) QED process
Energy is absorbed by plasmas ndash what happens to the background field
Coupling sfQED and classical processes
QED in intense fields
Creation of electron-positron pair transfers energy from background field (at interaction point)
χ 1 photon energy split evenly between electron and positron
For χ 1 most goes to one of the electron and positron
Coupling sfQED and classical processes
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
For χ 1 quantum depletion m vs classical a0
2m
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Laser absorption is increased (classically) because QED processes introduce new currents
Beyond the background field approximation
Depletion
In QED need to calculate transition rates between initial and final states that contain different numbers of photons
Does the LCFA let us take a simpler approach to calculating the effect of a QED avalanche on the background field
Beyond the background field approximation
Depletion
When does the quantum depletion have a serious effect on the background
Seipt et al PRL 118 154803 2017 for electron-beam laser collision need 10nC and a0 of 1000
Effects on angular distribution at lower intensity
Beyond the background field approximation
Depletion
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Positron production
Test bed
Electron-positron pair creation by the collision of high-energy particles with an intense laser pulse
eg wakefield accelerated electrons bremsstrahlung created gamma rayshellip
In the highly non-linear regime
Positron production
Test bed
Interaction can be modelled directly from QED (Di Piazza PRL 117 213201 2016)
Integrated full-scale QED-PIC simulations for wakefield acceleration plus photon and pair creation (Lobet et al PRAB 20 043401 2017)
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
Introduction
Goals
Understanding QED in laser-plasmas is necessary
Understanding QED in laser-plasmas is interesting
(Understanding QED in laser-plasmas is difficult)
Introduction
Goals
Understanding QED in laser-plasmas is necessary
Understanding QED in laser-plasmas is interesting
(Understanding QED in laser-plasmas is difficult)
Introduction
Goals
Understanding QED in laser-plasmas is necessary
Understanding QED in laser-plasmas is interesting
(Understanding QED in laser-plasmas is difficult)
Introduction
Quantum electrodynamics
Fundamental theory of the interaction between light and matter
Unifies quantum mechanics with special relativity
Charged particles interact via the emission and absorption of photons
Introduction
Quantum electrodynamics
Fundamental theory of the interaction between light and matter
Unifies quantum mechanics with special relativity
Charged particles interact via the emission and absorption of photons
Introduction
Quantum electrodynamics
Each vertex carries a factor of e the electron charge and a δ-function encoding the conservation of momentum
Simplest two photon emission (radiation reaction) and pair creation
Introduction
Quantum electrodynamics
Two-photon pair creation (Breit-Wheeler process) not observed experimentally (heavy ion collisions hohlraums)
Multiphoton Breit-Wheeler seen at SLAC (50 GeV electron beam into 1018 Wcm-2 laser 140 positrons) Non-linear index n = 5 6
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Reduce a hard problemby splitting it into a ldquoeasyrdquo part and a ldquosmallrdquo correction
Results take the form of a series expansion around the easy (ie unperturbed) solution
eg ground state energies in quantum mechanics
Beyond perturbative QED
Perturbation theory in quantum mechanics
Reduce a hard problemby splitting it into a ldquoeasyrdquo part and a ldquosmallrdquo correction
Results take the form of a series expansion around the easy (ie unperturbed) solution
eg ground state energies in quantum mechanics
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Zeeman effect Coulomb potential perturbed by static magnetic field
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
More = better
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
More = better
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
More = better
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
More = better
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
But the series diverges
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
But the series diverges
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory generically leads to divergent series
This has been known for a long time ndash see Bender and Wu Phys Rev 184 1231 (1969)
Besides infinities are interesting
Beyond perturbative QED
Perturbation theory in quantum mechanics
ldquoThe series is divergent therefore we may be able to do something with itrdquo - O Heaviside
ldquoThis is infinity here It could be infinity We donrsquot really donrsquot know But it could be It has to be something ndash but it could be infinity rightrdquo- D J Trump
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Use the integral definition of a factorial
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Use the integral definition of a factorial
Swap the summation and integration
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
If they dont the integrand has a pole on the real axis
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
If they dont the integrand has a pole on the real axis
This has physicalsignificance
Beyond perturbative QED
Perturbation theory in quantum mechanics
Recall the dispersion relation for an EM wave in a warm plasma
The permittivity has a pole where the phase velocity of the wave and the particle velocity are equal
Gives rise to Landau damping
This has physicalsignificance
Beyond perturbative QED
Perturbation theory in quantum mechanics
If the terms do not alternate in sign Borel summation gives you an imaginary term that is non-perturbative in the coupling strength
Non-perturbative in the sense that exp(-1x) has Taylor expansion about 0 that is 0 to all orders
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Divergent perturbative series with coefficients that do not alternate in sign
Zeeman effect Coulomb potential perturbed by static magnetic field
Divergent perturbative series with coefficients alternating in sign
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Ionization rate
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative Why perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Does the same occur in quantum field theory
After all perturbation theory has proved extraordinarily successful
Beyond perturbative QED
Perturbation theory in quantum mechanics
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
S has a non-perturbative imaginary part
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
The action for a static electric field acquires an imaginary part that is non-perturbative in the electric field strength
Stark effect = ionisation rate Here we get the pair-creation rate from the vacuum
Ecrit = 13times1018 Vm
Beyond perturbative QED
Perturbation theory in QED
How do we access fields of this magnitude in the lab
Important parameter is χ (ratio of electric field in electron rest frame to the critical field of QED)
Beyond perturbative QED
QED in intense fields
χ = 1 means the electron sees in its rest frame a field strong enough for non-perturbative effects to dominate
Low order terms are suppressed only high order terms (ie involving large numbers of background photons) contribute
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
What about arbitrary field structures
Beyond perturbative QED
QED in intense fields
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
What do we lose by doing this
Harmonics sub-harmonics interference resonanceshellip
When is it acceptable to do so
How much bigger than 1 must a0 be
Coupling sfQED and classical processes
Locally constant field approximation
Other constraints on PIC simulations
Size of timestep must be set to avoid multiple scatterings (constraint set by rate of photon emission is strongest)
C P Ridgers et al J Comp Phys 260 273 (2014)
The rates (not cross-sections) for photon and pair production are calculated in an equivalent system of fields with the same instantaneous value of χ
eg a static magnetic field in the ultrarelativistic limit T Erber Rev Mod Phys 38 626 (1966)
Coupling sfQED and classical processes
PIC + Monte Carlo
We assumed a classical background field
Contains sufficient energy that the field is not affected by a (single) QED process
Energy is absorbed by plasmas ndash what happens to the background field
Coupling sfQED and classical processes
QED in intense fields
Creation of electron-positron pair transfers energy from background field (at interaction point)
χ 1 photon energy split evenly between electron and positron
For χ 1 most goes to one of the electron and positron
Coupling sfQED and classical processes
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
For χ 1 quantum depletion m vs classical a0
2m
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Laser absorption is increased (classically) because QED processes introduce new currents
Beyond the background field approximation
Depletion
In QED need to calculate transition rates between initial and final states that contain different numbers of photons
Does the LCFA let us take a simpler approach to calculating the effect of a QED avalanche on the background field
Beyond the background field approximation
Depletion
When does the quantum depletion have a serious effect on the background
Seipt et al PRL 118 154803 2017 for electron-beam laser collision need 10nC and a0 of 1000
Effects on angular distribution at lower intensity
Beyond the background field approximation
Depletion
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Positron production
Test bed
Electron-positron pair creation by the collision of high-energy particles with an intense laser pulse
eg wakefield accelerated electrons bremsstrahlung created gamma rayshellip
In the highly non-linear regime
Positron production
Test bed
Interaction can be modelled directly from QED (Di Piazza PRL 117 213201 2016)
Integrated full-scale QED-PIC simulations for wakefield acceleration plus photon and pair creation (Lobet et al PRAB 20 043401 2017)
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
Introduction
Goals
Understanding QED in laser-plasmas is necessary
Understanding QED in laser-plasmas is interesting
(Understanding QED in laser-plasmas is difficult)
Introduction
Goals
Understanding QED in laser-plasmas is necessary
Understanding QED in laser-plasmas is interesting
(Understanding QED in laser-plasmas is difficult)
Introduction
Quantum electrodynamics
Fundamental theory of the interaction between light and matter
Unifies quantum mechanics with special relativity
Charged particles interact via the emission and absorption of photons
Introduction
Quantum electrodynamics
Fundamental theory of the interaction between light and matter
Unifies quantum mechanics with special relativity
Charged particles interact via the emission and absorption of photons
Introduction
Quantum electrodynamics
Each vertex carries a factor of e the electron charge and a δ-function encoding the conservation of momentum
Simplest two photon emission (radiation reaction) and pair creation
Introduction
Quantum electrodynamics
Two-photon pair creation (Breit-Wheeler process) not observed experimentally (heavy ion collisions hohlraums)
Multiphoton Breit-Wheeler seen at SLAC (50 GeV electron beam into 1018 Wcm-2 laser 140 positrons) Non-linear index n = 5 6
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Reduce a hard problemby splitting it into a ldquoeasyrdquo part and a ldquosmallrdquo correction
Results take the form of a series expansion around the easy (ie unperturbed) solution
eg ground state energies in quantum mechanics
Beyond perturbative QED
Perturbation theory in quantum mechanics
Reduce a hard problemby splitting it into a ldquoeasyrdquo part and a ldquosmallrdquo correction
Results take the form of a series expansion around the easy (ie unperturbed) solution
eg ground state energies in quantum mechanics
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Zeeman effect Coulomb potential perturbed by static magnetic field
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
More = better
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
More = better
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
More = better
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
More = better
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
But the series diverges
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
But the series diverges
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory generically leads to divergent series
This has been known for a long time ndash see Bender and Wu Phys Rev 184 1231 (1969)
Besides infinities are interesting
Beyond perturbative QED
Perturbation theory in quantum mechanics
ldquoThe series is divergent therefore we may be able to do something with itrdquo - O Heaviside
ldquoThis is infinity here It could be infinity We donrsquot really donrsquot know But it could be It has to be something ndash but it could be infinity rightrdquo- D J Trump
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Use the integral definition of a factorial
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Use the integral definition of a factorial
Swap the summation and integration
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
If they dont the integrand has a pole on the real axis
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
If they dont the integrand has a pole on the real axis
This has physicalsignificance
Beyond perturbative QED
Perturbation theory in quantum mechanics
Recall the dispersion relation for an EM wave in a warm plasma
The permittivity has a pole where the phase velocity of the wave and the particle velocity are equal
Gives rise to Landau damping
This has physicalsignificance
Beyond perturbative QED
Perturbation theory in quantum mechanics
If the terms do not alternate in sign Borel summation gives you an imaginary term that is non-perturbative in the coupling strength
Non-perturbative in the sense that exp(-1x) has Taylor expansion about 0 that is 0 to all orders
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Divergent perturbative series with coefficients that do not alternate in sign
Zeeman effect Coulomb potential perturbed by static magnetic field
Divergent perturbative series with coefficients alternating in sign
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Ionization rate
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative Why perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Does the same occur in quantum field theory
After all perturbation theory has proved extraordinarily successful
Beyond perturbative QED
Perturbation theory in quantum mechanics
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
S has a non-perturbative imaginary part
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
The action for a static electric field acquires an imaginary part that is non-perturbative in the electric field strength
Stark effect = ionisation rate Here we get the pair-creation rate from the vacuum
Ecrit = 13times1018 Vm
Beyond perturbative QED
Perturbation theory in QED
How do we access fields of this magnitude in the lab
Important parameter is χ (ratio of electric field in electron rest frame to the critical field of QED)
Beyond perturbative QED
QED in intense fields
χ = 1 means the electron sees in its rest frame a field strong enough for non-perturbative effects to dominate
Low order terms are suppressed only high order terms (ie involving large numbers of background photons) contribute
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
What about arbitrary field structures
Beyond perturbative QED
QED in intense fields
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
What do we lose by doing this
Harmonics sub-harmonics interference resonanceshellip
When is it acceptable to do so
How much bigger than 1 must a0 be
Coupling sfQED and classical processes
Locally constant field approximation
Other constraints on PIC simulations
Size of timestep must be set to avoid multiple scatterings (constraint set by rate of photon emission is strongest)
C P Ridgers et al J Comp Phys 260 273 (2014)
The rates (not cross-sections) for photon and pair production are calculated in an equivalent system of fields with the same instantaneous value of χ
eg a static magnetic field in the ultrarelativistic limit T Erber Rev Mod Phys 38 626 (1966)
Coupling sfQED and classical processes
PIC + Monte Carlo
We assumed a classical background field
Contains sufficient energy that the field is not affected by a (single) QED process
Energy is absorbed by plasmas ndash what happens to the background field
Coupling sfQED and classical processes
QED in intense fields
Creation of electron-positron pair transfers energy from background field (at interaction point)
χ 1 photon energy split evenly between electron and positron
For χ 1 most goes to one of the electron and positron
Coupling sfQED and classical processes
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
For χ 1 quantum depletion m vs classical a0
2m
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Laser absorption is increased (classically) because QED processes introduce new currents
Beyond the background field approximation
Depletion
In QED need to calculate transition rates between initial and final states that contain different numbers of photons
Does the LCFA let us take a simpler approach to calculating the effect of a QED avalanche on the background field
Beyond the background field approximation
Depletion
When does the quantum depletion have a serious effect on the background
Seipt et al PRL 118 154803 2017 for electron-beam laser collision need 10nC and a0 of 1000
Effects on angular distribution at lower intensity
Beyond the background field approximation
Depletion
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Positron production
Test bed
Electron-positron pair creation by the collision of high-energy particles with an intense laser pulse
eg wakefield accelerated electrons bremsstrahlung created gamma rayshellip
In the highly non-linear regime
Positron production
Test bed
Interaction can be modelled directly from QED (Di Piazza PRL 117 213201 2016)
Integrated full-scale QED-PIC simulations for wakefield acceleration plus photon and pair creation (Lobet et al PRAB 20 043401 2017)
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
Introduction
Goals
Understanding QED in laser-plasmas is necessary
Understanding QED in laser-plasmas is interesting
(Understanding QED in laser-plasmas is difficult)
Introduction
Quantum electrodynamics
Fundamental theory of the interaction between light and matter
Unifies quantum mechanics with special relativity
Charged particles interact via the emission and absorption of photons
Introduction
Quantum electrodynamics
Fundamental theory of the interaction between light and matter
Unifies quantum mechanics with special relativity
Charged particles interact via the emission and absorption of photons
Introduction
Quantum electrodynamics
Each vertex carries a factor of e the electron charge and a δ-function encoding the conservation of momentum
Simplest two photon emission (radiation reaction) and pair creation
Introduction
Quantum electrodynamics
Two-photon pair creation (Breit-Wheeler process) not observed experimentally (heavy ion collisions hohlraums)
Multiphoton Breit-Wheeler seen at SLAC (50 GeV electron beam into 1018 Wcm-2 laser 140 positrons) Non-linear index n = 5 6
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Reduce a hard problemby splitting it into a ldquoeasyrdquo part and a ldquosmallrdquo correction
Results take the form of a series expansion around the easy (ie unperturbed) solution
eg ground state energies in quantum mechanics
Beyond perturbative QED
Perturbation theory in quantum mechanics
Reduce a hard problemby splitting it into a ldquoeasyrdquo part and a ldquosmallrdquo correction
Results take the form of a series expansion around the easy (ie unperturbed) solution
eg ground state energies in quantum mechanics
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Zeeman effect Coulomb potential perturbed by static magnetic field
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
More = better
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
More = better
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
More = better
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
More = better
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
But the series diverges
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
But the series diverges
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory generically leads to divergent series
This has been known for a long time ndash see Bender and Wu Phys Rev 184 1231 (1969)
Besides infinities are interesting
Beyond perturbative QED
Perturbation theory in quantum mechanics
ldquoThe series is divergent therefore we may be able to do something with itrdquo - O Heaviside
ldquoThis is infinity here It could be infinity We donrsquot really donrsquot know But it could be It has to be something ndash but it could be infinity rightrdquo- D J Trump
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Use the integral definition of a factorial
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Use the integral definition of a factorial
Swap the summation and integration
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
If they dont the integrand has a pole on the real axis
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
If they dont the integrand has a pole on the real axis
This has physicalsignificance
Beyond perturbative QED
Perturbation theory in quantum mechanics
Recall the dispersion relation for an EM wave in a warm plasma
The permittivity has a pole where the phase velocity of the wave and the particle velocity are equal
Gives rise to Landau damping
This has physicalsignificance
Beyond perturbative QED
Perturbation theory in quantum mechanics
If the terms do not alternate in sign Borel summation gives you an imaginary term that is non-perturbative in the coupling strength
Non-perturbative in the sense that exp(-1x) has Taylor expansion about 0 that is 0 to all orders
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Divergent perturbative series with coefficients that do not alternate in sign
Zeeman effect Coulomb potential perturbed by static magnetic field
Divergent perturbative series with coefficients alternating in sign
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Ionization rate
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative Why perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Does the same occur in quantum field theory
After all perturbation theory has proved extraordinarily successful
Beyond perturbative QED
Perturbation theory in quantum mechanics
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
S has a non-perturbative imaginary part
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
The action for a static electric field acquires an imaginary part that is non-perturbative in the electric field strength
Stark effect = ionisation rate Here we get the pair-creation rate from the vacuum
Ecrit = 13times1018 Vm
Beyond perturbative QED
Perturbation theory in QED
How do we access fields of this magnitude in the lab
Important parameter is χ (ratio of electric field in electron rest frame to the critical field of QED)
Beyond perturbative QED
QED in intense fields
χ = 1 means the electron sees in its rest frame a field strong enough for non-perturbative effects to dominate
Low order terms are suppressed only high order terms (ie involving large numbers of background photons) contribute
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
What about arbitrary field structures
Beyond perturbative QED
QED in intense fields
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
What do we lose by doing this
Harmonics sub-harmonics interference resonanceshellip
When is it acceptable to do so
How much bigger than 1 must a0 be
Coupling sfQED and classical processes
Locally constant field approximation
Other constraints on PIC simulations
Size of timestep must be set to avoid multiple scatterings (constraint set by rate of photon emission is strongest)
C P Ridgers et al J Comp Phys 260 273 (2014)
The rates (not cross-sections) for photon and pair production are calculated in an equivalent system of fields with the same instantaneous value of χ
eg a static magnetic field in the ultrarelativistic limit T Erber Rev Mod Phys 38 626 (1966)
Coupling sfQED and classical processes
PIC + Monte Carlo
We assumed a classical background field
Contains sufficient energy that the field is not affected by a (single) QED process
Energy is absorbed by plasmas ndash what happens to the background field
Coupling sfQED and classical processes
QED in intense fields
Creation of electron-positron pair transfers energy from background field (at interaction point)
χ 1 photon energy split evenly between electron and positron
For χ 1 most goes to one of the electron and positron
Coupling sfQED and classical processes
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
For χ 1 quantum depletion m vs classical a0
2m
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Laser absorption is increased (classically) because QED processes introduce new currents
Beyond the background field approximation
Depletion
In QED need to calculate transition rates between initial and final states that contain different numbers of photons
Does the LCFA let us take a simpler approach to calculating the effect of a QED avalanche on the background field
Beyond the background field approximation
Depletion
When does the quantum depletion have a serious effect on the background
Seipt et al PRL 118 154803 2017 for electron-beam laser collision need 10nC and a0 of 1000
Effects on angular distribution at lower intensity
Beyond the background field approximation
Depletion
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Positron production
Test bed
Electron-positron pair creation by the collision of high-energy particles with an intense laser pulse
eg wakefield accelerated electrons bremsstrahlung created gamma rayshellip
In the highly non-linear regime
Positron production
Test bed
Interaction can be modelled directly from QED (Di Piazza PRL 117 213201 2016)
Integrated full-scale QED-PIC simulations for wakefield acceleration plus photon and pair creation (Lobet et al PRAB 20 043401 2017)
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
Introduction
Quantum electrodynamics
Fundamental theory of the interaction between light and matter
Unifies quantum mechanics with special relativity
Charged particles interact via the emission and absorption of photons
Introduction
Quantum electrodynamics
Fundamental theory of the interaction between light and matter
Unifies quantum mechanics with special relativity
Charged particles interact via the emission and absorption of photons
Introduction
Quantum electrodynamics
Each vertex carries a factor of e the electron charge and a δ-function encoding the conservation of momentum
Simplest two photon emission (radiation reaction) and pair creation
Introduction
Quantum electrodynamics
Two-photon pair creation (Breit-Wheeler process) not observed experimentally (heavy ion collisions hohlraums)
Multiphoton Breit-Wheeler seen at SLAC (50 GeV electron beam into 1018 Wcm-2 laser 140 positrons) Non-linear index n = 5 6
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Reduce a hard problemby splitting it into a ldquoeasyrdquo part and a ldquosmallrdquo correction
Results take the form of a series expansion around the easy (ie unperturbed) solution
eg ground state energies in quantum mechanics
Beyond perturbative QED
Perturbation theory in quantum mechanics
Reduce a hard problemby splitting it into a ldquoeasyrdquo part and a ldquosmallrdquo correction
Results take the form of a series expansion around the easy (ie unperturbed) solution
eg ground state energies in quantum mechanics
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Zeeman effect Coulomb potential perturbed by static magnetic field
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
More = better
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
More = better
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
More = better
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
More = better
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
But the series diverges
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
But the series diverges
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory generically leads to divergent series
This has been known for a long time ndash see Bender and Wu Phys Rev 184 1231 (1969)
Besides infinities are interesting
Beyond perturbative QED
Perturbation theory in quantum mechanics
ldquoThe series is divergent therefore we may be able to do something with itrdquo - O Heaviside
ldquoThis is infinity here It could be infinity We donrsquot really donrsquot know But it could be It has to be something ndash but it could be infinity rightrdquo- D J Trump
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Use the integral definition of a factorial
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Use the integral definition of a factorial
Swap the summation and integration
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
If they dont the integrand has a pole on the real axis
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
If they dont the integrand has a pole on the real axis
This has physicalsignificance
Beyond perturbative QED
Perturbation theory in quantum mechanics
Recall the dispersion relation for an EM wave in a warm plasma
The permittivity has a pole where the phase velocity of the wave and the particle velocity are equal
Gives rise to Landau damping
This has physicalsignificance
Beyond perturbative QED
Perturbation theory in quantum mechanics
If the terms do not alternate in sign Borel summation gives you an imaginary term that is non-perturbative in the coupling strength
Non-perturbative in the sense that exp(-1x) has Taylor expansion about 0 that is 0 to all orders
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Divergent perturbative series with coefficients that do not alternate in sign
Zeeman effect Coulomb potential perturbed by static magnetic field
Divergent perturbative series with coefficients alternating in sign
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Ionization rate
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative Why perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Does the same occur in quantum field theory
After all perturbation theory has proved extraordinarily successful
Beyond perturbative QED
Perturbation theory in quantum mechanics
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
S has a non-perturbative imaginary part
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
The action for a static electric field acquires an imaginary part that is non-perturbative in the electric field strength
Stark effect = ionisation rate Here we get the pair-creation rate from the vacuum
Ecrit = 13times1018 Vm
Beyond perturbative QED
Perturbation theory in QED
How do we access fields of this magnitude in the lab
Important parameter is χ (ratio of electric field in electron rest frame to the critical field of QED)
Beyond perturbative QED
QED in intense fields
χ = 1 means the electron sees in its rest frame a field strong enough for non-perturbative effects to dominate
Low order terms are suppressed only high order terms (ie involving large numbers of background photons) contribute
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
What about arbitrary field structures
Beyond perturbative QED
QED in intense fields
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
What do we lose by doing this
Harmonics sub-harmonics interference resonanceshellip
When is it acceptable to do so
How much bigger than 1 must a0 be
Coupling sfQED and classical processes
Locally constant field approximation
Other constraints on PIC simulations
Size of timestep must be set to avoid multiple scatterings (constraint set by rate of photon emission is strongest)
C P Ridgers et al J Comp Phys 260 273 (2014)
The rates (not cross-sections) for photon and pair production are calculated in an equivalent system of fields with the same instantaneous value of χ
eg a static magnetic field in the ultrarelativistic limit T Erber Rev Mod Phys 38 626 (1966)
Coupling sfQED and classical processes
PIC + Monte Carlo
We assumed a classical background field
Contains sufficient energy that the field is not affected by a (single) QED process
Energy is absorbed by plasmas ndash what happens to the background field
Coupling sfQED and classical processes
QED in intense fields
Creation of electron-positron pair transfers energy from background field (at interaction point)
χ 1 photon energy split evenly between electron and positron
For χ 1 most goes to one of the electron and positron
Coupling sfQED and classical processes
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
For χ 1 quantum depletion m vs classical a0
2m
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Laser absorption is increased (classically) because QED processes introduce new currents
Beyond the background field approximation
Depletion
In QED need to calculate transition rates between initial and final states that contain different numbers of photons
Does the LCFA let us take a simpler approach to calculating the effect of a QED avalanche on the background field
Beyond the background field approximation
Depletion
When does the quantum depletion have a serious effect on the background
Seipt et al PRL 118 154803 2017 for electron-beam laser collision need 10nC and a0 of 1000
Effects on angular distribution at lower intensity
Beyond the background field approximation
Depletion
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Positron production
Test bed
Electron-positron pair creation by the collision of high-energy particles with an intense laser pulse
eg wakefield accelerated electrons bremsstrahlung created gamma rayshellip
In the highly non-linear regime
Positron production
Test bed
Interaction can be modelled directly from QED (Di Piazza PRL 117 213201 2016)
Integrated full-scale QED-PIC simulations for wakefield acceleration plus photon and pair creation (Lobet et al PRAB 20 043401 2017)
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
Introduction
Quantum electrodynamics
Fundamental theory of the interaction between light and matter
Unifies quantum mechanics with special relativity
Charged particles interact via the emission and absorption of photons
Introduction
Quantum electrodynamics
Each vertex carries a factor of e the electron charge and a δ-function encoding the conservation of momentum
Simplest two photon emission (radiation reaction) and pair creation
Introduction
Quantum electrodynamics
Two-photon pair creation (Breit-Wheeler process) not observed experimentally (heavy ion collisions hohlraums)
Multiphoton Breit-Wheeler seen at SLAC (50 GeV electron beam into 1018 Wcm-2 laser 140 positrons) Non-linear index n = 5 6
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Reduce a hard problemby splitting it into a ldquoeasyrdquo part and a ldquosmallrdquo correction
Results take the form of a series expansion around the easy (ie unperturbed) solution
eg ground state energies in quantum mechanics
Beyond perturbative QED
Perturbation theory in quantum mechanics
Reduce a hard problemby splitting it into a ldquoeasyrdquo part and a ldquosmallrdquo correction
Results take the form of a series expansion around the easy (ie unperturbed) solution
eg ground state energies in quantum mechanics
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Zeeman effect Coulomb potential perturbed by static magnetic field
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
More = better
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
More = better
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
More = better
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
More = better
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
But the series diverges
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
But the series diverges
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory generically leads to divergent series
This has been known for a long time ndash see Bender and Wu Phys Rev 184 1231 (1969)
Besides infinities are interesting
Beyond perturbative QED
Perturbation theory in quantum mechanics
ldquoThe series is divergent therefore we may be able to do something with itrdquo - O Heaviside
ldquoThis is infinity here It could be infinity We donrsquot really donrsquot know But it could be It has to be something ndash but it could be infinity rightrdquo- D J Trump
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Use the integral definition of a factorial
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Use the integral definition of a factorial
Swap the summation and integration
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
If they dont the integrand has a pole on the real axis
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
If they dont the integrand has a pole on the real axis
This has physicalsignificance
Beyond perturbative QED
Perturbation theory in quantum mechanics
Recall the dispersion relation for an EM wave in a warm plasma
The permittivity has a pole where the phase velocity of the wave and the particle velocity are equal
Gives rise to Landau damping
This has physicalsignificance
Beyond perturbative QED
Perturbation theory in quantum mechanics
If the terms do not alternate in sign Borel summation gives you an imaginary term that is non-perturbative in the coupling strength
Non-perturbative in the sense that exp(-1x) has Taylor expansion about 0 that is 0 to all orders
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Divergent perturbative series with coefficients that do not alternate in sign
Zeeman effect Coulomb potential perturbed by static magnetic field
Divergent perturbative series with coefficients alternating in sign
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Ionization rate
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative Why perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Does the same occur in quantum field theory
After all perturbation theory has proved extraordinarily successful
Beyond perturbative QED
Perturbation theory in quantum mechanics
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
S has a non-perturbative imaginary part
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
The action for a static electric field acquires an imaginary part that is non-perturbative in the electric field strength
Stark effect = ionisation rate Here we get the pair-creation rate from the vacuum
Ecrit = 13times1018 Vm
Beyond perturbative QED
Perturbation theory in QED
How do we access fields of this magnitude in the lab
Important parameter is χ (ratio of electric field in electron rest frame to the critical field of QED)
Beyond perturbative QED
QED in intense fields
χ = 1 means the electron sees in its rest frame a field strong enough for non-perturbative effects to dominate
Low order terms are suppressed only high order terms (ie involving large numbers of background photons) contribute
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
What about arbitrary field structures
Beyond perturbative QED
QED in intense fields
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
What do we lose by doing this
Harmonics sub-harmonics interference resonanceshellip
When is it acceptable to do so
How much bigger than 1 must a0 be
Coupling sfQED and classical processes
Locally constant field approximation
Other constraints on PIC simulations
Size of timestep must be set to avoid multiple scatterings (constraint set by rate of photon emission is strongest)
C P Ridgers et al J Comp Phys 260 273 (2014)
The rates (not cross-sections) for photon and pair production are calculated in an equivalent system of fields with the same instantaneous value of χ
eg a static magnetic field in the ultrarelativistic limit T Erber Rev Mod Phys 38 626 (1966)
Coupling sfQED and classical processes
PIC + Monte Carlo
We assumed a classical background field
Contains sufficient energy that the field is not affected by a (single) QED process
Energy is absorbed by plasmas ndash what happens to the background field
Coupling sfQED and classical processes
QED in intense fields
Creation of electron-positron pair transfers energy from background field (at interaction point)
χ 1 photon energy split evenly between electron and positron
For χ 1 most goes to one of the electron and positron
Coupling sfQED and classical processes
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
For χ 1 quantum depletion m vs classical a0
2m
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Laser absorption is increased (classically) because QED processes introduce new currents
Beyond the background field approximation
Depletion
In QED need to calculate transition rates between initial and final states that contain different numbers of photons
Does the LCFA let us take a simpler approach to calculating the effect of a QED avalanche on the background field
Beyond the background field approximation
Depletion
When does the quantum depletion have a serious effect on the background
Seipt et al PRL 118 154803 2017 for electron-beam laser collision need 10nC and a0 of 1000
Effects on angular distribution at lower intensity
Beyond the background field approximation
Depletion
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Positron production
Test bed
Electron-positron pair creation by the collision of high-energy particles with an intense laser pulse
eg wakefield accelerated electrons bremsstrahlung created gamma rayshellip
In the highly non-linear regime
Positron production
Test bed
Interaction can be modelled directly from QED (Di Piazza PRL 117 213201 2016)
Integrated full-scale QED-PIC simulations for wakefield acceleration plus photon and pair creation (Lobet et al PRAB 20 043401 2017)
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
Introduction
Quantum electrodynamics
Each vertex carries a factor of e the electron charge and a δ-function encoding the conservation of momentum
Simplest two photon emission (radiation reaction) and pair creation
Introduction
Quantum electrodynamics
Two-photon pair creation (Breit-Wheeler process) not observed experimentally (heavy ion collisions hohlraums)
Multiphoton Breit-Wheeler seen at SLAC (50 GeV electron beam into 1018 Wcm-2 laser 140 positrons) Non-linear index n = 5 6
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Reduce a hard problemby splitting it into a ldquoeasyrdquo part and a ldquosmallrdquo correction
Results take the form of a series expansion around the easy (ie unperturbed) solution
eg ground state energies in quantum mechanics
Beyond perturbative QED
Perturbation theory in quantum mechanics
Reduce a hard problemby splitting it into a ldquoeasyrdquo part and a ldquosmallrdquo correction
Results take the form of a series expansion around the easy (ie unperturbed) solution
eg ground state energies in quantum mechanics
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Zeeman effect Coulomb potential perturbed by static magnetic field
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
More = better
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
More = better
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
More = better
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
More = better
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
But the series diverges
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
But the series diverges
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory generically leads to divergent series
This has been known for a long time ndash see Bender and Wu Phys Rev 184 1231 (1969)
Besides infinities are interesting
Beyond perturbative QED
Perturbation theory in quantum mechanics
ldquoThe series is divergent therefore we may be able to do something with itrdquo - O Heaviside
ldquoThis is infinity here It could be infinity We donrsquot really donrsquot know But it could be It has to be something ndash but it could be infinity rightrdquo- D J Trump
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Use the integral definition of a factorial
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Use the integral definition of a factorial
Swap the summation and integration
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
If they dont the integrand has a pole on the real axis
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
If they dont the integrand has a pole on the real axis
This has physicalsignificance
Beyond perturbative QED
Perturbation theory in quantum mechanics
Recall the dispersion relation for an EM wave in a warm plasma
The permittivity has a pole where the phase velocity of the wave and the particle velocity are equal
Gives rise to Landau damping
This has physicalsignificance
Beyond perturbative QED
Perturbation theory in quantum mechanics
If the terms do not alternate in sign Borel summation gives you an imaginary term that is non-perturbative in the coupling strength
Non-perturbative in the sense that exp(-1x) has Taylor expansion about 0 that is 0 to all orders
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Divergent perturbative series with coefficients that do not alternate in sign
Zeeman effect Coulomb potential perturbed by static magnetic field
Divergent perturbative series with coefficients alternating in sign
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Ionization rate
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative Why perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Does the same occur in quantum field theory
After all perturbation theory has proved extraordinarily successful
Beyond perturbative QED
Perturbation theory in quantum mechanics
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
S has a non-perturbative imaginary part
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
The action for a static electric field acquires an imaginary part that is non-perturbative in the electric field strength
Stark effect = ionisation rate Here we get the pair-creation rate from the vacuum
Ecrit = 13times1018 Vm
Beyond perturbative QED
Perturbation theory in QED
How do we access fields of this magnitude in the lab
Important parameter is χ (ratio of electric field in electron rest frame to the critical field of QED)
Beyond perturbative QED
QED in intense fields
χ = 1 means the electron sees in its rest frame a field strong enough for non-perturbative effects to dominate
Low order terms are suppressed only high order terms (ie involving large numbers of background photons) contribute
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
What about arbitrary field structures
Beyond perturbative QED
QED in intense fields
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
What do we lose by doing this
Harmonics sub-harmonics interference resonanceshellip
When is it acceptable to do so
How much bigger than 1 must a0 be
Coupling sfQED and classical processes
Locally constant field approximation
Other constraints on PIC simulations
Size of timestep must be set to avoid multiple scatterings (constraint set by rate of photon emission is strongest)
C P Ridgers et al J Comp Phys 260 273 (2014)
The rates (not cross-sections) for photon and pair production are calculated in an equivalent system of fields with the same instantaneous value of χ
eg a static magnetic field in the ultrarelativistic limit T Erber Rev Mod Phys 38 626 (1966)
Coupling sfQED and classical processes
PIC + Monte Carlo
We assumed a classical background field
Contains sufficient energy that the field is not affected by a (single) QED process
Energy is absorbed by plasmas ndash what happens to the background field
Coupling sfQED and classical processes
QED in intense fields
Creation of electron-positron pair transfers energy from background field (at interaction point)
χ 1 photon energy split evenly between electron and positron
For χ 1 most goes to one of the electron and positron
Coupling sfQED and classical processes
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
For χ 1 quantum depletion m vs classical a0
2m
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Laser absorption is increased (classically) because QED processes introduce new currents
Beyond the background field approximation
Depletion
In QED need to calculate transition rates between initial and final states that contain different numbers of photons
Does the LCFA let us take a simpler approach to calculating the effect of a QED avalanche on the background field
Beyond the background field approximation
Depletion
When does the quantum depletion have a serious effect on the background
Seipt et al PRL 118 154803 2017 for electron-beam laser collision need 10nC and a0 of 1000
Effects on angular distribution at lower intensity
Beyond the background field approximation
Depletion
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Positron production
Test bed
Electron-positron pair creation by the collision of high-energy particles with an intense laser pulse
eg wakefield accelerated electrons bremsstrahlung created gamma rayshellip
In the highly non-linear regime
Positron production
Test bed
Interaction can be modelled directly from QED (Di Piazza PRL 117 213201 2016)
Integrated full-scale QED-PIC simulations for wakefield acceleration plus photon and pair creation (Lobet et al PRAB 20 043401 2017)
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
Introduction
Quantum electrodynamics
Two-photon pair creation (Breit-Wheeler process) not observed experimentally (heavy ion collisions hohlraums)
Multiphoton Breit-Wheeler seen at SLAC (50 GeV electron beam into 1018 Wcm-2 laser 140 positrons) Non-linear index n = 5 6
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Reduce a hard problemby splitting it into a ldquoeasyrdquo part and a ldquosmallrdquo correction
Results take the form of a series expansion around the easy (ie unperturbed) solution
eg ground state energies in quantum mechanics
Beyond perturbative QED
Perturbation theory in quantum mechanics
Reduce a hard problemby splitting it into a ldquoeasyrdquo part and a ldquosmallrdquo correction
Results take the form of a series expansion around the easy (ie unperturbed) solution
eg ground state energies in quantum mechanics
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Zeeman effect Coulomb potential perturbed by static magnetic field
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
More = better
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
More = better
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
More = better
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
More = better
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
But the series diverges
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
But the series diverges
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory generically leads to divergent series
This has been known for a long time ndash see Bender and Wu Phys Rev 184 1231 (1969)
Besides infinities are interesting
Beyond perturbative QED
Perturbation theory in quantum mechanics
ldquoThe series is divergent therefore we may be able to do something with itrdquo - O Heaviside
ldquoThis is infinity here It could be infinity We donrsquot really donrsquot know But it could be It has to be something ndash but it could be infinity rightrdquo- D J Trump
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Use the integral definition of a factorial
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Use the integral definition of a factorial
Swap the summation and integration
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
If they dont the integrand has a pole on the real axis
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
If they dont the integrand has a pole on the real axis
This has physicalsignificance
Beyond perturbative QED
Perturbation theory in quantum mechanics
Recall the dispersion relation for an EM wave in a warm plasma
The permittivity has a pole where the phase velocity of the wave and the particle velocity are equal
Gives rise to Landau damping
This has physicalsignificance
Beyond perturbative QED
Perturbation theory in quantum mechanics
If the terms do not alternate in sign Borel summation gives you an imaginary term that is non-perturbative in the coupling strength
Non-perturbative in the sense that exp(-1x) has Taylor expansion about 0 that is 0 to all orders
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Divergent perturbative series with coefficients that do not alternate in sign
Zeeman effect Coulomb potential perturbed by static magnetic field
Divergent perturbative series with coefficients alternating in sign
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Ionization rate
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative Why perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Does the same occur in quantum field theory
After all perturbation theory has proved extraordinarily successful
Beyond perturbative QED
Perturbation theory in quantum mechanics
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
S has a non-perturbative imaginary part
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
The action for a static electric field acquires an imaginary part that is non-perturbative in the electric field strength
Stark effect = ionisation rate Here we get the pair-creation rate from the vacuum
Ecrit = 13times1018 Vm
Beyond perturbative QED
Perturbation theory in QED
How do we access fields of this magnitude in the lab
Important parameter is χ (ratio of electric field in electron rest frame to the critical field of QED)
Beyond perturbative QED
QED in intense fields
χ = 1 means the electron sees in its rest frame a field strong enough for non-perturbative effects to dominate
Low order terms are suppressed only high order terms (ie involving large numbers of background photons) contribute
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
What about arbitrary field structures
Beyond perturbative QED
QED in intense fields
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
What do we lose by doing this
Harmonics sub-harmonics interference resonanceshellip
When is it acceptable to do so
How much bigger than 1 must a0 be
Coupling sfQED and classical processes
Locally constant field approximation
Other constraints on PIC simulations
Size of timestep must be set to avoid multiple scatterings (constraint set by rate of photon emission is strongest)
C P Ridgers et al J Comp Phys 260 273 (2014)
The rates (not cross-sections) for photon and pair production are calculated in an equivalent system of fields with the same instantaneous value of χ
eg a static magnetic field in the ultrarelativistic limit T Erber Rev Mod Phys 38 626 (1966)
Coupling sfQED and classical processes
PIC + Monte Carlo
We assumed a classical background field
Contains sufficient energy that the field is not affected by a (single) QED process
Energy is absorbed by plasmas ndash what happens to the background field
Coupling sfQED and classical processes
QED in intense fields
Creation of electron-positron pair transfers energy from background field (at interaction point)
χ 1 photon energy split evenly between electron and positron
For χ 1 most goes to one of the electron and positron
Coupling sfQED and classical processes
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
For χ 1 quantum depletion m vs classical a0
2m
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Laser absorption is increased (classically) because QED processes introduce new currents
Beyond the background field approximation
Depletion
In QED need to calculate transition rates between initial and final states that contain different numbers of photons
Does the LCFA let us take a simpler approach to calculating the effect of a QED avalanche on the background field
Beyond the background field approximation
Depletion
When does the quantum depletion have a serious effect on the background
Seipt et al PRL 118 154803 2017 for electron-beam laser collision need 10nC and a0 of 1000
Effects on angular distribution at lower intensity
Beyond the background field approximation
Depletion
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Positron production
Test bed
Electron-positron pair creation by the collision of high-energy particles with an intense laser pulse
eg wakefield accelerated electrons bremsstrahlung created gamma rayshellip
In the highly non-linear regime
Positron production
Test bed
Interaction can be modelled directly from QED (Di Piazza PRL 117 213201 2016)
Integrated full-scale QED-PIC simulations for wakefield acceleration plus photon and pair creation (Lobet et al PRAB 20 043401 2017)
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Reduce a hard problemby splitting it into a ldquoeasyrdquo part and a ldquosmallrdquo correction
Results take the form of a series expansion around the easy (ie unperturbed) solution
eg ground state energies in quantum mechanics
Beyond perturbative QED
Perturbation theory in quantum mechanics
Reduce a hard problemby splitting it into a ldquoeasyrdquo part and a ldquosmallrdquo correction
Results take the form of a series expansion around the easy (ie unperturbed) solution
eg ground state energies in quantum mechanics
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Zeeman effect Coulomb potential perturbed by static magnetic field
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
More = better
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
More = better
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
More = better
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
More = better
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
But the series diverges
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
But the series diverges
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory generically leads to divergent series
This has been known for a long time ndash see Bender and Wu Phys Rev 184 1231 (1969)
Besides infinities are interesting
Beyond perturbative QED
Perturbation theory in quantum mechanics
ldquoThe series is divergent therefore we may be able to do something with itrdquo - O Heaviside
ldquoThis is infinity here It could be infinity We donrsquot really donrsquot know But it could be It has to be something ndash but it could be infinity rightrdquo- D J Trump
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Use the integral definition of a factorial
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Use the integral definition of a factorial
Swap the summation and integration
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
If they dont the integrand has a pole on the real axis
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
If they dont the integrand has a pole on the real axis
This has physicalsignificance
Beyond perturbative QED
Perturbation theory in quantum mechanics
Recall the dispersion relation for an EM wave in a warm plasma
The permittivity has a pole where the phase velocity of the wave and the particle velocity are equal
Gives rise to Landau damping
This has physicalsignificance
Beyond perturbative QED
Perturbation theory in quantum mechanics
If the terms do not alternate in sign Borel summation gives you an imaginary term that is non-perturbative in the coupling strength
Non-perturbative in the sense that exp(-1x) has Taylor expansion about 0 that is 0 to all orders
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Divergent perturbative series with coefficients that do not alternate in sign
Zeeman effect Coulomb potential perturbed by static magnetic field
Divergent perturbative series with coefficients alternating in sign
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Ionization rate
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative Why perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Does the same occur in quantum field theory
After all perturbation theory has proved extraordinarily successful
Beyond perturbative QED
Perturbation theory in quantum mechanics
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
S has a non-perturbative imaginary part
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
The action for a static electric field acquires an imaginary part that is non-perturbative in the electric field strength
Stark effect = ionisation rate Here we get the pair-creation rate from the vacuum
Ecrit = 13times1018 Vm
Beyond perturbative QED
Perturbation theory in QED
How do we access fields of this magnitude in the lab
Important parameter is χ (ratio of electric field in electron rest frame to the critical field of QED)
Beyond perturbative QED
QED in intense fields
χ = 1 means the electron sees in its rest frame a field strong enough for non-perturbative effects to dominate
Low order terms are suppressed only high order terms (ie involving large numbers of background photons) contribute
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
What about arbitrary field structures
Beyond perturbative QED
QED in intense fields
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
What do we lose by doing this
Harmonics sub-harmonics interference resonanceshellip
When is it acceptable to do so
How much bigger than 1 must a0 be
Coupling sfQED and classical processes
Locally constant field approximation
Other constraints on PIC simulations
Size of timestep must be set to avoid multiple scatterings (constraint set by rate of photon emission is strongest)
C P Ridgers et al J Comp Phys 260 273 (2014)
The rates (not cross-sections) for photon and pair production are calculated in an equivalent system of fields with the same instantaneous value of χ
eg a static magnetic field in the ultrarelativistic limit T Erber Rev Mod Phys 38 626 (1966)
Coupling sfQED and classical processes
PIC + Monte Carlo
We assumed a classical background field
Contains sufficient energy that the field is not affected by a (single) QED process
Energy is absorbed by plasmas ndash what happens to the background field
Coupling sfQED and classical processes
QED in intense fields
Creation of electron-positron pair transfers energy from background field (at interaction point)
χ 1 photon energy split evenly between electron and positron
For χ 1 most goes to one of the electron and positron
Coupling sfQED and classical processes
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
For χ 1 quantum depletion m vs classical a0
2m
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Laser absorption is increased (classically) because QED processes introduce new currents
Beyond the background field approximation
Depletion
In QED need to calculate transition rates between initial and final states that contain different numbers of photons
Does the LCFA let us take a simpler approach to calculating the effect of a QED avalanche on the background field
Beyond the background field approximation
Depletion
When does the quantum depletion have a serious effect on the background
Seipt et al PRL 118 154803 2017 for electron-beam laser collision need 10nC and a0 of 1000
Effects on angular distribution at lower intensity
Beyond the background field approximation
Depletion
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Positron production
Test bed
Electron-positron pair creation by the collision of high-energy particles with an intense laser pulse
eg wakefield accelerated electrons bremsstrahlung created gamma rayshellip
In the highly non-linear regime
Positron production
Test bed
Interaction can be modelled directly from QED (Di Piazza PRL 117 213201 2016)
Integrated full-scale QED-PIC simulations for wakefield acceleration plus photon and pair creation (Lobet et al PRAB 20 043401 2017)
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Reduce a hard problemby splitting it into a ldquoeasyrdquo part and a ldquosmallrdquo correction
Results take the form of a series expansion around the easy (ie unperturbed) solution
eg ground state energies in quantum mechanics
Beyond perturbative QED
Perturbation theory in quantum mechanics
Reduce a hard problemby splitting it into a ldquoeasyrdquo part and a ldquosmallrdquo correction
Results take the form of a series expansion around the easy (ie unperturbed) solution
eg ground state energies in quantum mechanics
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Zeeman effect Coulomb potential perturbed by static magnetic field
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
More = better
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
More = better
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
More = better
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
More = better
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
But the series diverges
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
But the series diverges
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory generically leads to divergent series
This has been known for a long time ndash see Bender and Wu Phys Rev 184 1231 (1969)
Besides infinities are interesting
Beyond perturbative QED
Perturbation theory in quantum mechanics
ldquoThe series is divergent therefore we may be able to do something with itrdquo - O Heaviside
ldquoThis is infinity here It could be infinity We donrsquot really donrsquot know But it could be It has to be something ndash but it could be infinity rightrdquo- D J Trump
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Use the integral definition of a factorial
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Use the integral definition of a factorial
Swap the summation and integration
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
If they dont the integrand has a pole on the real axis
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
If they dont the integrand has a pole on the real axis
This has physicalsignificance
Beyond perturbative QED
Perturbation theory in quantum mechanics
Recall the dispersion relation for an EM wave in a warm plasma
The permittivity has a pole where the phase velocity of the wave and the particle velocity are equal
Gives rise to Landau damping
This has physicalsignificance
Beyond perturbative QED
Perturbation theory in quantum mechanics
If the terms do not alternate in sign Borel summation gives you an imaginary term that is non-perturbative in the coupling strength
Non-perturbative in the sense that exp(-1x) has Taylor expansion about 0 that is 0 to all orders
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Divergent perturbative series with coefficients that do not alternate in sign
Zeeman effect Coulomb potential perturbed by static magnetic field
Divergent perturbative series with coefficients alternating in sign
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Ionization rate
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative Why perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Does the same occur in quantum field theory
After all perturbation theory has proved extraordinarily successful
Beyond perturbative QED
Perturbation theory in quantum mechanics
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
S has a non-perturbative imaginary part
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
The action for a static electric field acquires an imaginary part that is non-perturbative in the electric field strength
Stark effect = ionisation rate Here we get the pair-creation rate from the vacuum
Ecrit = 13times1018 Vm
Beyond perturbative QED
Perturbation theory in QED
How do we access fields of this magnitude in the lab
Important parameter is χ (ratio of electric field in electron rest frame to the critical field of QED)
Beyond perturbative QED
QED in intense fields
χ = 1 means the electron sees in its rest frame a field strong enough for non-perturbative effects to dominate
Low order terms are suppressed only high order terms (ie involving large numbers of background photons) contribute
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
What about arbitrary field structures
Beyond perturbative QED
QED in intense fields
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
What do we lose by doing this
Harmonics sub-harmonics interference resonanceshellip
When is it acceptable to do so
How much bigger than 1 must a0 be
Coupling sfQED and classical processes
Locally constant field approximation
Other constraints on PIC simulations
Size of timestep must be set to avoid multiple scatterings (constraint set by rate of photon emission is strongest)
C P Ridgers et al J Comp Phys 260 273 (2014)
The rates (not cross-sections) for photon and pair production are calculated in an equivalent system of fields with the same instantaneous value of χ
eg a static magnetic field in the ultrarelativistic limit T Erber Rev Mod Phys 38 626 (1966)
Coupling sfQED and classical processes
PIC + Monte Carlo
We assumed a classical background field
Contains sufficient energy that the field is not affected by a (single) QED process
Energy is absorbed by plasmas ndash what happens to the background field
Coupling sfQED and classical processes
QED in intense fields
Creation of electron-positron pair transfers energy from background field (at interaction point)
χ 1 photon energy split evenly between electron and positron
For χ 1 most goes to one of the electron and positron
Coupling sfQED and classical processes
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
For χ 1 quantum depletion m vs classical a0
2m
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Laser absorption is increased (classically) because QED processes introduce new currents
Beyond the background field approximation
Depletion
In QED need to calculate transition rates between initial and final states that contain different numbers of photons
Does the LCFA let us take a simpler approach to calculating the effect of a QED avalanche on the background field
Beyond the background field approximation
Depletion
When does the quantum depletion have a serious effect on the background
Seipt et al PRL 118 154803 2017 for electron-beam laser collision need 10nC and a0 of 1000
Effects on angular distribution at lower intensity
Beyond the background field approximation
Depletion
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Positron production
Test bed
Electron-positron pair creation by the collision of high-energy particles with an intense laser pulse
eg wakefield accelerated electrons bremsstrahlung created gamma rayshellip
In the highly non-linear regime
Positron production
Test bed
Interaction can be modelled directly from QED (Di Piazza PRL 117 213201 2016)
Integrated full-scale QED-PIC simulations for wakefield acceleration plus photon and pair creation (Lobet et al PRAB 20 043401 2017)
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
Reduce a hard problemby splitting it into a ldquoeasyrdquo part and a ldquosmallrdquo correction
Results take the form of a series expansion around the easy (ie unperturbed) solution
eg ground state energies in quantum mechanics
Beyond perturbative QED
Perturbation theory in quantum mechanics
Reduce a hard problemby splitting it into a ldquoeasyrdquo part and a ldquosmallrdquo correction
Results take the form of a series expansion around the easy (ie unperturbed) solution
eg ground state energies in quantum mechanics
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Zeeman effect Coulomb potential perturbed by static magnetic field
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
More = better
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
More = better
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
More = better
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
More = better
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
But the series diverges
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
But the series diverges
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory generically leads to divergent series
This has been known for a long time ndash see Bender and Wu Phys Rev 184 1231 (1969)
Besides infinities are interesting
Beyond perturbative QED
Perturbation theory in quantum mechanics
ldquoThe series is divergent therefore we may be able to do something with itrdquo - O Heaviside
ldquoThis is infinity here It could be infinity We donrsquot really donrsquot know But it could be It has to be something ndash but it could be infinity rightrdquo- D J Trump
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Use the integral definition of a factorial
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Use the integral definition of a factorial
Swap the summation and integration
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
If they dont the integrand has a pole on the real axis
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
If they dont the integrand has a pole on the real axis
This has physicalsignificance
Beyond perturbative QED
Perturbation theory in quantum mechanics
Recall the dispersion relation for an EM wave in a warm plasma
The permittivity has a pole where the phase velocity of the wave and the particle velocity are equal
Gives rise to Landau damping
This has physicalsignificance
Beyond perturbative QED
Perturbation theory in quantum mechanics
If the terms do not alternate in sign Borel summation gives you an imaginary term that is non-perturbative in the coupling strength
Non-perturbative in the sense that exp(-1x) has Taylor expansion about 0 that is 0 to all orders
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Divergent perturbative series with coefficients that do not alternate in sign
Zeeman effect Coulomb potential perturbed by static magnetic field
Divergent perturbative series with coefficients alternating in sign
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Ionization rate
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative Why perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Does the same occur in quantum field theory
After all perturbation theory has proved extraordinarily successful
Beyond perturbative QED
Perturbation theory in quantum mechanics
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
S has a non-perturbative imaginary part
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
The action for a static electric field acquires an imaginary part that is non-perturbative in the electric field strength
Stark effect = ionisation rate Here we get the pair-creation rate from the vacuum
Ecrit = 13times1018 Vm
Beyond perturbative QED
Perturbation theory in QED
How do we access fields of this magnitude in the lab
Important parameter is χ (ratio of electric field in electron rest frame to the critical field of QED)
Beyond perturbative QED
QED in intense fields
χ = 1 means the electron sees in its rest frame a field strong enough for non-perturbative effects to dominate
Low order terms are suppressed only high order terms (ie involving large numbers of background photons) contribute
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
What about arbitrary field structures
Beyond perturbative QED
QED in intense fields
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
What do we lose by doing this
Harmonics sub-harmonics interference resonanceshellip
When is it acceptable to do so
How much bigger than 1 must a0 be
Coupling sfQED and classical processes
Locally constant field approximation
Other constraints on PIC simulations
Size of timestep must be set to avoid multiple scatterings (constraint set by rate of photon emission is strongest)
C P Ridgers et al J Comp Phys 260 273 (2014)
The rates (not cross-sections) for photon and pair production are calculated in an equivalent system of fields with the same instantaneous value of χ
eg a static magnetic field in the ultrarelativistic limit T Erber Rev Mod Phys 38 626 (1966)
Coupling sfQED and classical processes
PIC + Monte Carlo
We assumed a classical background field
Contains sufficient energy that the field is not affected by a (single) QED process
Energy is absorbed by plasmas ndash what happens to the background field
Coupling sfQED and classical processes
QED in intense fields
Creation of electron-positron pair transfers energy from background field (at interaction point)
χ 1 photon energy split evenly between electron and positron
For χ 1 most goes to one of the electron and positron
Coupling sfQED and classical processes
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
For χ 1 quantum depletion m vs classical a0
2m
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Laser absorption is increased (classically) because QED processes introduce new currents
Beyond the background field approximation
Depletion
In QED need to calculate transition rates between initial and final states that contain different numbers of photons
Does the LCFA let us take a simpler approach to calculating the effect of a QED avalanche on the background field
Beyond the background field approximation
Depletion
When does the quantum depletion have a serious effect on the background
Seipt et al PRL 118 154803 2017 for electron-beam laser collision need 10nC and a0 of 1000
Effects on angular distribution at lower intensity
Beyond the background field approximation
Depletion
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Positron production
Test bed
Electron-positron pair creation by the collision of high-energy particles with an intense laser pulse
eg wakefield accelerated electrons bremsstrahlung created gamma rayshellip
In the highly non-linear regime
Positron production
Test bed
Interaction can be modelled directly from QED (Di Piazza PRL 117 213201 2016)
Integrated full-scale QED-PIC simulations for wakefield acceleration plus photon and pair creation (Lobet et al PRAB 20 043401 2017)
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
Reduce a hard problemby splitting it into a ldquoeasyrdquo part and a ldquosmallrdquo correction
Results take the form of a series expansion around the easy (ie unperturbed) solution
eg ground state energies in quantum mechanics
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Zeeman effect Coulomb potential perturbed by static magnetic field
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
More = better
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
More = better
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
More = better
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
More = better
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
But the series diverges
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
But the series diverges
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory generically leads to divergent series
This has been known for a long time ndash see Bender and Wu Phys Rev 184 1231 (1969)
Besides infinities are interesting
Beyond perturbative QED
Perturbation theory in quantum mechanics
ldquoThe series is divergent therefore we may be able to do something with itrdquo - O Heaviside
ldquoThis is infinity here It could be infinity We donrsquot really donrsquot know But it could be It has to be something ndash but it could be infinity rightrdquo- D J Trump
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Use the integral definition of a factorial
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Use the integral definition of a factorial
Swap the summation and integration
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
If they dont the integrand has a pole on the real axis
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
If they dont the integrand has a pole on the real axis
This has physicalsignificance
Beyond perturbative QED
Perturbation theory in quantum mechanics
Recall the dispersion relation for an EM wave in a warm plasma
The permittivity has a pole where the phase velocity of the wave and the particle velocity are equal
Gives rise to Landau damping
This has physicalsignificance
Beyond perturbative QED
Perturbation theory in quantum mechanics
If the terms do not alternate in sign Borel summation gives you an imaginary term that is non-perturbative in the coupling strength
Non-perturbative in the sense that exp(-1x) has Taylor expansion about 0 that is 0 to all orders
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Divergent perturbative series with coefficients that do not alternate in sign
Zeeman effect Coulomb potential perturbed by static magnetic field
Divergent perturbative series with coefficients alternating in sign
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Ionization rate
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative Why perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Does the same occur in quantum field theory
After all perturbation theory has proved extraordinarily successful
Beyond perturbative QED
Perturbation theory in quantum mechanics
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
S has a non-perturbative imaginary part
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
The action for a static electric field acquires an imaginary part that is non-perturbative in the electric field strength
Stark effect = ionisation rate Here we get the pair-creation rate from the vacuum
Ecrit = 13times1018 Vm
Beyond perturbative QED
Perturbation theory in QED
How do we access fields of this magnitude in the lab
Important parameter is χ (ratio of electric field in electron rest frame to the critical field of QED)
Beyond perturbative QED
QED in intense fields
χ = 1 means the electron sees in its rest frame a field strong enough for non-perturbative effects to dominate
Low order terms are suppressed only high order terms (ie involving large numbers of background photons) contribute
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
What about arbitrary field structures
Beyond perturbative QED
QED in intense fields
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
What do we lose by doing this
Harmonics sub-harmonics interference resonanceshellip
When is it acceptable to do so
How much bigger than 1 must a0 be
Coupling sfQED and classical processes
Locally constant field approximation
Other constraints on PIC simulations
Size of timestep must be set to avoid multiple scatterings (constraint set by rate of photon emission is strongest)
C P Ridgers et al J Comp Phys 260 273 (2014)
The rates (not cross-sections) for photon and pair production are calculated in an equivalent system of fields with the same instantaneous value of χ
eg a static magnetic field in the ultrarelativistic limit T Erber Rev Mod Phys 38 626 (1966)
Coupling sfQED and classical processes
PIC + Monte Carlo
We assumed a classical background field
Contains sufficient energy that the field is not affected by a (single) QED process
Energy is absorbed by plasmas ndash what happens to the background field
Coupling sfQED and classical processes
QED in intense fields
Creation of electron-positron pair transfers energy from background field (at interaction point)
χ 1 photon energy split evenly between electron and positron
For χ 1 most goes to one of the electron and positron
Coupling sfQED and classical processes
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
For χ 1 quantum depletion m vs classical a0
2m
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Laser absorption is increased (classically) because QED processes introduce new currents
Beyond the background field approximation
Depletion
In QED need to calculate transition rates between initial and final states that contain different numbers of photons
Does the LCFA let us take a simpler approach to calculating the effect of a QED avalanche on the background field
Beyond the background field approximation
Depletion
When does the quantum depletion have a serious effect on the background
Seipt et al PRL 118 154803 2017 for electron-beam laser collision need 10nC and a0 of 1000
Effects on angular distribution at lower intensity
Beyond the background field approximation
Depletion
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Positron production
Test bed
Electron-positron pair creation by the collision of high-energy particles with an intense laser pulse
eg wakefield accelerated electrons bremsstrahlung created gamma rayshellip
In the highly non-linear regime
Positron production
Test bed
Interaction can be modelled directly from QED (Di Piazza PRL 117 213201 2016)
Integrated full-scale QED-PIC simulations for wakefield acceleration plus photon and pair creation (Lobet et al PRAB 20 043401 2017)
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
Stark effect Coulomb potential perturbed by static electric field
Zeeman effect Coulomb potential perturbed by static magnetic field
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
More = better
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
More = better
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
More = better
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
More = better
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
But the series diverges
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
But the series diverges
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory generically leads to divergent series
This has been known for a long time ndash see Bender and Wu Phys Rev 184 1231 (1969)
Besides infinities are interesting
Beyond perturbative QED
Perturbation theory in quantum mechanics
ldquoThe series is divergent therefore we may be able to do something with itrdquo - O Heaviside
ldquoThis is infinity here It could be infinity We donrsquot really donrsquot know But it could be It has to be something ndash but it could be infinity rightrdquo- D J Trump
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Use the integral definition of a factorial
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Use the integral definition of a factorial
Swap the summation and integration
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
If they dont the integrand has a pole on the real axis
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
If they dont the integrand has a pole on the real axis
This has physicalsignificance
Beyond perturbative QED
Perturbation theory in quantum mechanics
Recall the dispersion relation for an EM wave in a warm plasma
The permittivity has a pole where the phase velocity of the wave and the particle velocity are equal
Gives rise to Landau damping
This has physicalsignificance
Beyond perturbative QED
Perturbation theory in quantum mechanics
If the terms do not alternate in sign Borel summation gives you an imaginary term that is non-perturbative in the coupling strength
Non-perturbative in the sense that exp(-1x) has Taylor expansion about 0 that is 0 to all orders
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Divergent perturbative series with coefficients that do not alternate in sign
Zeeman effect Coulomb potential perturbed by static magnetic field
Divergent perturbative series with coefficients alternating in sign
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Ionization rate
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative Why perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Does the same occur in quantum field theory
After all perturbation theory has proved extraordinarily successful
Beyond perturbative QED
Perturbation theory in quantum mechanics
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
S has a non-perturbative imaginary part
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
The action for a static electric field acquires an imaginary part that is non-perturbative in the electric field strength
Stark effect = ionisation rate Here we get the pair-creation rate from the vacuum
Ecrit = 13times1018 Vm
Beyond perturbative QED
Perturbation theory in QED
How do we access fields of this magnitude in the lab
Important parameter is χ (ratio of electric field in electron rest frame to the critical field of QED)
Beyond perturbative QED
QED in intense fields
χ = 1 means the electron sees in its rest frame a field strong enough for non-perturbative effects to dominate
Low order terms are suppressed only high order terms (ie involving large numbers of background photons) contribute
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
What about arbitrary field structures
Beyond perturbative QED
QED in intense fields
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
What do we lose by doing this
Harmonics sub-harmonics interference resonanceshellip
When is it acceptable to do so
How much bigger than 1 must a0 be
Coupling sfQED and classical processes
Locally constant field approximation
Other constraints on PIC simulations
Size of timestep must be set to avoid multiple scatterings (constraint set by rate of photon emission is strongest)
C P Ridgers et al J Comp Phys 260 273 (2014)
The rates (not cross-sections) for photon and pair production are calculated in an equivalent system of fields with the same instantaneous value of χ
eg a static magnetic field in the ultrarelativistic limit T Erber Rev Mod Phys 38 626 (1966)
Coupling sfQED and classical processes
PIC + Monte Carlo
We assumed a classical background field
Contains sufficient energy that the field is not affected by a (single) QED process
Energy is absorbed by plasmas ndash what happens to the background field
Coupling sfQED and classical processes
QED in intense fields
Creation of electron-positron pair transfers energy from background field (at interaction point)
χ 1 photon energy split evenly between electron and positron
For χ 1 most goes to one of the electron and positron
Coupling sfQED and classical processes
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
For χ 1 quantum depletion m vs classical a0
2m
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Laser absorption is increased (classically) because QED processes introduce new currents
Beyond the background field approximation
Depletion
In QED need to calculate transition rates between initial and final states that contain different numbers of photons
Does the LCFA let us take a simpler approach to calculating the effect of a QED avalanche on the background field
Beyond the background field approximation
Depletion
When does the quantum depletion have a serious effect on the background
Seipt et al PRL 118 154803 2017 for electron-beam laser collision need 10nC and a0 of 1000
Effects on angular distribution at lower intensity
Beyond the background field approximation
Depletion
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Positron production
Test bed
Electron-positron pair creation by the collision of high-energy particles with an intense laser pulse
eg wakefield accelerated electrons bremsstrahlung created gamma rayshellip
In the highly non-linear regime
Positron production
Test bed
Interaction can be modelled directly from QED (Di Piazza PRL 117 213201 2016)
Integrated full-scale QED-PIC simulations for wakefield acceleration plus photon and pair creation (Lobet et al PRAB 20 043401 2017)
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
More = better
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
More = better
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
More = better
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
More = better
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
But the series diverges
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
But the series diverges
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory generically leads to divergent series
This has been known for a long time ndash see Bender and Wu Phys Rev 184 1231 (1969)
Besides infinities are interesting
Beyond perturbative QED
Perturbation theory in quantum mechanics
ldquoThe series is divergent therefore we may be able to do something with itrdquo - O Heaviside
ldquoThis is infinity here It could be infinity We donrsquot really donrsquot know But it could be It has to be something ndash but it could be infinity rightrdquo- D J Trump
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Use the integral definition of a factorial
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Use the integral definition of a factorial
Swap the summation and integration
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
If they dont the integrand has a pole on the real axis
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
If they dont the integrand has a pole on the real axis
This has physicalsignificance
Beyond perturbative QED
Perturbation theory in quantum mechanics
Recall the dispersion relation for an EM wave in a warm plasma
The permittivity has a pole where the phase velocity of the wave and the particle velocity are equal
Gives rise to Landau damping
This has physicalsignificance
Beyond perturbative QED
Perturbation theory in quantum mechanics
If the terms do not alternate in sign Borel summation gives you an imaginary term that is non-perturbative in the coupling strength
Non-perturbative in the sense that exp(-1x) has Taylor expansion about 0 that is 0 to all orders
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Divergent perturbative series with coefficients that do not alternate in sign
Zeeman effect Coulomb potential perturbed by static magnetic field
Divergent perturbative series with coefficients alternating in sign
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Ionization rate
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative Why perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Does the same occur in quantum field theory
After all perturbation theory has proved extraordinarily successful
Beyond perturbative QED
Perturbation theory in quantum mechanics
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
S has a non-perturbative imaginary part
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
The action for a static electric field acquires an imaginary part that is non-perturbative in the electric field strength
Stark effect = ionisation rate Here we get the pair-creation rate from the vacuum
Ecrit = 13times1018 Vm
Beyond perturbative QED
Perturbation theory in QED
How do we access fields of this magnitude in the lab
Important parameter is χ (ratio of electric field in electron rest frame to the critical field of QED)
Beyond perturbative QED
QED in intense fields
χ = 1 means the electron sees in its rest frame a field strong enough for non-perturbative effects to dominate
Low order terms are suppressed only high order terms (ie involving large numbers of background photons) contribute
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
What about arbitrary field structures
Beyond perturbative QED
QED in intense fields
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
What do we lose by doing this
Harmonics sub-harmonics interference resonanceshellip
When is it acceptable to do so
How much bigger than 1 must a0 be
Coupling sfQED and classical processes
Locally constant field approximation
Other constraints on PIC simulations
Size of timestep must be set to avoid multiple scatterings (constraint set by rate of photon emission is strongest)
C P Ridgers et al J Comp Phys 260 273 (2014)
The rates (not cross-sections) for photon and pair production are calculated in an equivalent system of fields with the same instantaneous value of χ
eg a static magnetic field in the ultrarelativistic limit T Erber Rev Mod Phys 38 626 (1966)
Coupling sfQED and classical processes
PIC + Monte Carlo
We assumed a classical background field
Contains sufficient energy that the field is not affected by a (single) QED process
Energy is absorbed by plasmas ndash what happens to the background field
Coupling sfQED and classical processes
QED in intense fields
Creation of electron-positron pair transfers energy from background field (at interaction point)
χ 1 photon energy split evenly between electron and positron
For χ 1 most goes to one of the electron and positron
Coupling sfQED and classical processes
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
For χ 1 quantum depletion m vs classical a0
2m
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Laser absorption is increased (classically) because QED processes introduce new currents
Beyond the background field approximation
Depletion
In QED need to calculate transition rates between initial and final states that contain different numbers of photons
Does the LCFA let us take a simpler approach to calculating the effect of a QED avalanche on the background field
Beyond the background field approximation
Depletion
When does the quantum depletion have a serious effect on the background
Seipt et al PRL 118 154803 2017 for electron-beam laser collision need 10nC and a0 of 1000
Effects on angular distribution at lower intensity
Beyond the background field approximation
Depletion
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Positron production
Test bed
Electron-positron pair creation by the collision of high-energy particles with an intense laser pulse
eg wakefield accelerated electrons bremsstrahlung created gamma rayshellip
In the highly non-linear regime
Positron production
Test bed
Interaction can be modelled directly from QED (Di Piazza PRL 117 213201 2016)
Integrated full-scale QED-PIC simulations for wakefield acceleration plus photon and pair creation (Lobet et al PRAB 20 043401 2017)
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
More = better
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
More = better
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
More = better
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
More = better
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
But the series diverges
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
But the series diverges
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory generically leads to divergent series
This has been known for a long time ndash see Bender and Wu Phys Rev 184 1231 (1969)
Besides infinities are interesting
Beyond perturbative QED
Perturbation theory in quantum mechanics
ldquoThe series is divergent therefore we may be able to do something with itrdquo - O Heaviside
ldquoThis is infinity here It could be infinity We donrsquot really donrsquot know But it could be It has to be something ndash but it could be infinity rightrdquo- D J Trump
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Use the integral definition of a factorial
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Use the integral definition of a factorial
Swap the summation and integration
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
If they dont the integrand has a pole on the real axis
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
If they dont the integrand has a pole on the real axis
This has physicalsignificance
Beyond perturbative QED
Perturbation theory in quantum mechanics
Recall the dispersion relation for an EM wave in a warm plasma
The permittivity has a pole where the phase velocity of the wave and the particle velocity are equal
Gives rise to Landau damping
This has physicalsignificance
Beyond perturbative QED
Perturbation theory in quantum mechanics
If the terms do not alternate in sign Borel summation gives you an imaginary term that is non-perturbative in the coupling strength
Non-perturbative in the sense that exp(-1x) has Taylor expansion about 0 that is 0 to all orders
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Divergent perturbative series with coefficients that do not alternate in sign
Zeeman effect Coulomb potential perturbed by static magnetic field
Divergent perturbative series with coefficients alternating in sign
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Ionization rate
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative Why perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Does the same occur in quantum field theory
After all perturbation theory has proved extraordinarily successful
Beyond perturbative QED
Perturbation theory in quantum mechanics
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
S has a non-perturbative imaginary part
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
The action for a static electric field acquires an imaginary part that is non-perturbative in the electric field strength
Stark effect = ionisation rate Here we get the pair-creation rate from the vacuum
Ecrit = 13times1018 Vm
Beyond perturbative QED
Perturbation theory in QED
How do we access fields of this magnitude in the lab
Important parameter is χ (ratio of electric field in electron rest frame to the critical field of QED)
Beyond perturbative QED
QED in intense fields
χ = 1 means the electron sees in its rest frame a field strong enough for non-perturbative effects to dominate
Low order terms are suppressed only high order terms (ie involving large numbers of background photons) contribute
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
What about arbitrary field structures
Beyond perturbative QED
QED in intense fields
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
What do we lose by doing this
Harmonics sub-harmonics interference resonanceshellip
When is it acceptable to do so
How much bigger than 1 must a0 be
Coupling sfQED and classical processes
Locally constant field approximation
Other constraints on PIC simulations
Size of timestep must be set to avoid multiple scatterings (constraint set by rate of photon emission is strongest)
C P Ridgers et al J Comp Phys 260 273 (2014)
The rates (not cross-sections) for photon and pair production are calculated in an equivalent system of fields with the same instantaneous value of χ
eg a static magnetic field in the ultrarelativistic limit T Erber Rev Mod Phys 38 626 (1966)
Coupling sfQED and classical processes
PIC + Monte Carlo
We assumed a classical background field
Contains sufficient energy that the field is not affected by a (single) QED process
Energy is absorbed by plasmas ndash what happens to the background field
Coupling sfQED and classical processes
QED in intense fields
Creation of electron-positron pair transfers energy from background field (at interaction point)
χ 1 photon energy split evenly between electron and positron
For χ 1 most goes to one of the electron and positron
Coupling sfQED and classical processes
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
For χ 1 quantum depletion m vs classical a0
2m
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Laser absorption is increased (classically) because QED processes introduce new currents
Beyond the background field approximation
Depletion
In QED need to calculate transition rates between initial and final states that contain different numbers of photons
Does the LCFA let us take a simpler approach to calculating the effect of a QED avalanche on the background field
Beyond the background field approximation
Depletion
When does the quantum depletion have a serious effect on the background
Seipt et al PRL 118 154803 2017 for electron-beam laser collision need 10nC and a0 of 1000
Effects on angular distribution at lower intensity
Beyond the background field approximation
Depletion
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Positron production
Test bed
Electron-positron pair creation by the collision of high-energy particles with an intense laser pulse
eg wakefield accelerated electrons bremsstrahlung created gamma rayshellip
In the highly non-linear regime
Positron production
Test bed
Interaction can be modelled directly from QED (Di Piazza PRL 117 213201 2016)
Integrated full-scale QED-PIC simulations for wakefield acceleration plus photon and pair creation (Lobet et al PRAB 20 043401 2017)
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
More = better
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
More = better
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
But the series diverges
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
But the series diverges
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory generically leads to divergent series
This has been known for a long time ndash see Bender and Wu Phys Rev 184 1231 (1969)
Besides infinities are interesting
Beyond perturbative QED
Perturbation theory in quantum mechanics
ldquoThe series is divergent therefore we may be able to do something with itrdquo - O Heaviside
ldquoThis is infinity here It could be infinity We donrsquot really donrsquot know But it could be It has to be something ndash but it could be infinity rightrdquo- D J Trump
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Use the integral definition of a factorial
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Use the integral definition of a factorial
Swap the summation and integration
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
If they dont the integrand has a pole on the real axis
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
If they dont the integrand has a pole on the real axis
This has physicalsignificance
Beyond perturbative QED
Perturbation theory in quantum mechanics
Recall the dispersion relation for an EM wave in a warm plasma
The permittivity has a pole where the phase velocity of the wave and the particle velocity are equal
Gives rise to Landau damping
This has physicalsignificance
Beyond perturbative QED
Perturbation theory in quantum mechanics
If the terms do not alternate in sign Borel summation gives you an imaginary term that is non-perturbative in the coupling strength
Non-perturbative in the sense that exp(-1x) has Taylor expansion about 0 that is 0 to all orders
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Divergent perturbative series with coefficients that do not alternate in sign
Zeeman effect Coulomb potential perturbed by static magnetic field
Divergent perturbative series with coefficients alternating in sign
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Ionization rate
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative Why perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Does the same occur in quantum field theory
After all perturbation theory has proved extraordinarily successful
Beyond perturbative QED
Perturbation theory in quantum mechanics
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
S has a non-perturbative imaginary part
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
The action for a static electric field acquires an imaginary part that is non-perturbative in the electric field strength
Stark effect = ionisation rate Here we get the pair-creation rate from the vacuum
Ecrit = 13times1018 Vm
Beyond perturbative QED
Perturbation theory in QED
How do we access fields of this magnitude in the lab
Important parameter is χ (ratio of electric field in electron rest frame to the critical field of QED)
Beyond perturbative QED
QED in intense fields
χ = 1 means the electron sees in its rest frame a field strong enough for non-perturbative effects to dominate
Low order terms are suppressed only high order terms (ie involving large numbers of background photons) contribute
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
What about arbitrary field structures
Beyond perturbative QED
QED in intense fields
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
What do we lose by doing this
Harmonics sub-harmonics interference resonanceshellip
When is it acceptable to do so
How much bigger than 1 must a0 be
Coupling sfQED and classical processes
Locally constant field approximation
Other constraints on PIC simulations
Size of timestep must be set to avoid multiple scatterings (constraint set by rate of photon emission is strongest)
C P Ridgers et al J Comp Phys 260 273 (2014)
The rates (not cross-sections) for photon and pair production are calculated in an equivalent system of fields with the same instantaneous value of χ
eg a static magnetic field in the ultrarelativistic limit T Erber Rev Mod Phys 38 626 (1966)
Coupling sfQED and classical processes
PIC + Monte Carlo
We assumed a classical background field
Contains sufficient energy that the field is not affected by a (single) QED process
Energy is absorbed by plasmas ndash what happens to the background field
Coupling sfQED and classical processes
QED in intense fields
Creation of electron-positron pair transfers energy from background field (at interaction point)
χ 1 photon energy split evenly between electron and positron
For χ 1 most goes to one of the electron and positron
Coupling sfQED and classical processes
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
For χ 1 quantum depletion m vs classical a0
2m
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Laser absorption is increased (classically) because QED processes introduce new currents
Beyond the background field approximation
Depletion
In QED need to calculate transition rates between initial and final states that contain different numbers of photons
Does the LCFA let us take a simpler approach to calculating the effect of a QED avalanche on the background field
Beyond the background field approximation
Depletion
When does the quantum depletion have a serious effect on the background
Seipt et al PRL 118 154803 2017 for electron-beam laser collision need 10nC and a0 of 1000
Effects on angular distribution at lower intensity
Beyond the background field approximation
Depletion
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Positron production
Test bed
Electron-positron pair creation by the collision of high-energy particles with an intense laser pulse
eg wakefield accelerated electrons bremsstrahlung created gamma rayshellip
In the highly non-linear regime
Positron production
Test bed
Interaction can be modelled directly from QED (Di Piazza PRL 117 213201 2016)
Integrated full-scale QED-PIC simulations for wakefield acceleration plus photon and pair creation (Lobet et al PRAB 20 043401 2017)
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
But the series diverges
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
But the series diverges
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory generically leads to divergent series
This has been known for a long time ndash see Bender and Wu Phys Rev 184 1231 (1969)
Besides infinities are interesting
Beyond perturbative QED
Perturbation theory in quantum mechanics
ldquoThe series is divergent therefore we may be able to do something with itrdquo - O Heaviside
ldquoThis is infinity here It could be infinity We donrsquot really donrsquot know But it could be It has to be something ndash but it could be infinity rightrdquo- D J Trump
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Use the integral definition of a factorial
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Use the integral definition of a factorial
Swap the summation and integration
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
If they dont the integrand has a pole on the real axis
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
If they dont the integrand has a pole on the real axis
This has physicalsignificance
Beyond perturbative QED
Perturbation theory in quantum mechanics
Recall the dispersion relation for an EM wave in a warm plasma
The permittivity has a pole where the phase velocity of the wave and the particle velocity are equal
Gives rise to Landau damping
This has physicalsignificance
Beyond perturbative QED
Perturbation theory in quantum mechanics
If the terms do not alternate in sign Borel summation gives you an imaginary term that is non-perturbative in the coupling strength
Non-perturbative in the sense that exp(-1x) has Taylor expansion about 0 that is 0 to all orders
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Divergent perturbative series with coefficients that do not alternate in sign
Zeeman effect Coulomb potential perturbed by static magnetic field
Divergent perturbative series with coefficients alternating in sign
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Ionization rate
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative Why perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Does the same occur in quantum field theory
After all perturbation theory has proved extraordinarily successful
Beyond perturbative QED
Perturbation theory in quantum mechanics
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
S has a non-perturbative imaginary part
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
The action for a static electric field acquires an imaginary part that is non-perturbative in the electric field strength
Stark effect = ionisation rate Here we get the pair-creation rate from the vacuum
Ecrit = 13times1018 Vm
Beyond perturbative QED
Perturbation theory in QED
How do we access fields of this magnitude in the lab
Important parameter is χ (ratio of electric field in electron rest frame to the critical field of QED)
Beyond perturbative QED
QED in intense fields
χ = 1 means the electron sees in its rest frame a field strong enough for non-perturbative effects to dominate
Low order terms are suppressed only high order terms (ie involving large numbers of background photons) contribute
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
What about arbitrary field structures
Beyond perturbative QED
QED in intense fields
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
What do we lose by doing this
Harmonics sub-harmonics interference resonanceshellip
When is it acceptable to do so
How much bigger than 1 must a0 be
Coupling sfQED and classical processes
Locally constant field approximation
Other constraints on PIC simulations
Size of timestep must be set to avoid multiple scatterings (constraint set by rate of photon emission is strongest)
C P Ridgers et al J Comp Phys 260 273 (2014)
The rates (not cross-sections) for photon and pair production are calculated in an equivalent system of fields with the same instantaneous value of χ
eg a static magnetic field in the ultrarelativistic limit T Erber Rev Mod Phys 38 626 (1966)
Coupling sfQED and classical processes
PIC + Monte Carlo
We assumed a classical background field
Contains sufficient energy that the field is not affected by a (single) QED process
Energy is absorbed by plasmas ndash what happens to the background field
Coupling sfQED and classical processes
QED in intense fields
Creation of electron-positron pair transfers energy from background field (at interaction point)
χ 1 photon energy split evenly between electron and positron
For χ 1 most goes to one of the electron and positron
Coupling sfQED and classical processes
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
For χ 1 quantum depletion m vs classical a0
2m
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Laser absorption is increased (classically) because QED processes introduce new currents
Beyond the background field approximation
Depletion
In QED need to calculate transition rates between initial and final states that contain different numbers of photons
Does the LCFA let us take a simpler approach to calculating the effect of a QED avalanche on the background field
Beyond the background field approximation
Depletion
When does the quantum depletion have a serious effect on the background
Seipt et al PRL 118 154803 2017 for electron-beam laser collision need 10nC and a0 of 1000
Effects on angular distribution at lower intensity
Beyond the background field approximation
Depletion
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Positron production
Test bed
Electron-positron pair creation by the collision of high-energy particles with an intense laser pulse
eg wakefield accelerated electrons bremsstrahlung created gamma rayshellip
In the highly non-linear regime
Positron production
Test bed
Interaction can be modelled directly from QED (Di Piazza PRL 117 213201 2016)
Integrated full-scale QED-PIC simulations for wakefield acceleration plus photon and pair creation (Lobet et al PRAB 20 043401 2017)
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
Perturbation theory generically leads to divergent series
This has been known for a long time ndash see Bender and Wu Phys Rev 184 1231 (1969)
Besides infinities are interesting
Beyond perturbative QED
Perturbation theory in quantum mechanics
ldquoThe series is divergent therefore we may be able to do something with itrdquo - O Heaviside
ldquoThis is infinity here It could be infinity We donrsquot really donrsquot know But it could be It has to be something ndash but it could be infinity rightrdquo- D J Trump
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Use the integral definition of a factorial
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Use the integral definition of a factorial
Swap the summation and integration
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
If they dont the integrand has a pole on the real axis
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
If they dont the integrand has a pole on the real axis
This has physicalsignificance
Beyond perturbative QED
Perturbation theory in quantum mechanics
Recall the dispersion relation for an EM wave in a warm plasma
The permittivity has a pole where the phase velocity of the wave and the particle velocity are equal
Gives rise to Landau damping
This has physicalsignificance
Beyond perturbative QED
Perturbation theory in quantum mechanics
If the terms do not alternate in sign Borel summation gives you an imaginary term that is non-perturbative in the coupling strength
Non-perturbative in the sense that exp(-1x) has Taylor expansion about 0 that is 0 to all orders
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Divergent perturbative series with coefficients that do not alternate in sign
Zeeman effect Coulomb potential perturbed by static magnetic field
Divergent perturbative series with coefficients alternating in sign
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Ionization rate
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative Why perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Does the same occur in quantum field theory
After all perturbation theory has proved extraordinarily successful
Beyond perturbative QED
Perturbation theory in quantum mechanics
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
S has a non-perturbative imaginary part
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
The action for a static electric field acquires an imaginary part that is non-perturbative in the electric field strength
Stark effect = ionisation rate Here we get the pair-creation rate from the vacuum
Ecrit = 13times1018 Vm
Beyond perturbative QED
Perturbation theory in QED
How do we access fields of this magnitude in the lab
Important parameter is χ (ratio of electric field in electron rest frame to the critical field of QED)
Beyond perturbative QED
QED in intense fields
χ = 1 means the electron sees in its rest frame a field strong enough for non-perturbative effects to dominate
Low order terms are suppressed only high order terms (ie involving large numbers of background photons) contribute
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
What about arbitrary field structures
Beyond perturbative QED
QED in intense fields
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
What do we lose by doing this
Harmonics sub-harmonics interference resonanceshellip
When is it acceptable to do so
How much bigger than 1 must a0 be
Coupling sfQED and classical processes
Locally constant field approximation
Other constraints on PIC simulations
Size of timestep must be set to avoid multiple scatterings (constraint set by rate of photon emission is strongest)
C P Ridgers et al J Comp Phys 260 273 (2014)
The rates (not cross-sections) for photon and pair production are calculated in an equivalent system of fields with the same instantaneous value of χ
eg a static magnetic field in the ultrarelativistic limit T Erber Rev Mod Phys 38 626 (1966)
Coupling sfQED and classical processes
PIC + Monte Carlo
We assumed a classical background field
Contains sufficient energy that the field is not affected by a (single) QED process
Energy is absorbed by plasmas ndash what happens to the background field
Coupling sfQED and classical processes
QED in intense fields
Creation of electron-positron pair transfers energy from background field (at interaction point)
χ 1 photon energy split evenly between electron and positron
For χ 1 most goes to one of the electron and positron
Coupling sfQED and classical processes
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
For χ 1 quantum depletion m vs classical a0
2m
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Laser absorption is increased (classically) because QED processes introduce new currents
Beyond the background field approximation
Depletion
In QED need to calculate transition rates between initial and final states that contain different numbers of photons
Does the LCFA let us take a simpler approach to calculating the effect of a QED avalanche on the background field
Beyond the background field approximation
Depletion
When does the quantum depletion have a serious effect on the background
Seipt et al PRL 118 154803 2017 for electron-beam laser collision need 10nC and a0 of 1000
Effects on angular distribution at lower intensity
Beyond the background field approximation
Depletion
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Positron production
Test bed
Electron-positron pair creation by the collision of high-energy particles with an intense laser pulse
eg wakefield accelerated electrons bremsstrahlung created gamma rayshellip
In the highly non-linear regime
Positron production
Test bed
Interaction can be modelled directly from QED (Di Piazza PRL 117 213201 2016)
Integrated full-scale QED-PIC simulations for wakefield acceleration plus photon and pair creation (Lobet et al PRAB 20 043401 2017)
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
ldquoThe series is divergent therefore we may be able to do something with itrdquo - O Heaviside
ldquoThis is infinity here It could be infinity We donrsquot really donrsquot know But it could be It has to be something ndash but it could be infinity rightrdquo- D J Trump
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Use the integral definition of a factorial
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Use the integral definition of a factorial
Swap the summation and integration
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
If they dont the integrand has a pole on the real axis
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
If they dont the integrand has a pole on the real axis
This has physicalsignificance
Beyond perturbative QED
Perturbation theory in quantum mechanics
Recall the dispersion relation for an EM wave in a warm plasma
The permittivity has a pole where the phase velocity of the wave and the particle velocity are equal
Gives rise to Landau damping
This has physicalsignificance
Beyond perturbative QED
Perturbation theory in quantum mechanics
If the terms do not alternate in sign Borel summation gives you an imaginary term that is non-perturbative in the coupling strength
Non-perturbative in the sense that exp(-1x) has Taylor expansion about 0 that is 0 to all orders
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Divergent perturbative series with coefficients that do not alternate in sign
Zeeman effect Coulomb potential perturbed by static magnetic field
Divergent perturbative series with coefficients alternating in sign
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Ionization rate
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative Why perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Does the same occur in quantum field theory
After all perturbation theory has proved extraordinarily successful
Beyond perturbative QED
Perturbation theory in quantum mechanics
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
S has a non-perturbative imaginary part
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
The action for a static electric field acquires an imaginary part that is non-perturbative in the electric field strength
Stark effect = ionisation rate Here we get the pair-creation rate from the vacuum
Ecrit = 13times1018 Vm
Beyond perturbative QED
Perturbation theory in QED
How do we access fields of this magnitude in the lab
Important parameter is χ (ratio of electric field in electron rest frame to the critical field of QED)
Beyond perturbative QED
QED in intense fields
χ = 1 means the electron sees in its rest frame a field strong enough for non-perturbative effects to dominate
Low order terms are suppressed only high order terms (ie involving large numbers of background photons) contribute
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
What about arbitrary field structures
Beyond perturbative QED
QED in intense fields
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
What do we lose by doing this
Harmonics sub-harmonics interference resonanceshellip
When is it acceptable to do so
How much bigger than 1 must a0 be
Coupling sfQED and classical processes
Locally constant field approximation
Other constraints on PIC simulations
Size of timestep must be set to avoid multiple scatterings (constraint set by rate of photon emission is strongest)
C P Ridgers et al J Comp Phys 260 273 (2014)
The rates (not cross-sections) for photon and pair production are calculated in an equivalent system of fields with the same instantaneous value of χ
eg a static magnetic field in the ultrarelativistic limit T Erber Rev Mod Phys 38 626 (1966)
Coupling sfQED and classical processes
PIC + Monte Carlo
We assumed a classical background field
Contains sufficient energy that the field is not affected by a (single) QED process
Energy is absorbed by plasmas ndash what happens to the background field
Coupling sfQED and classical processes
QED in intense fields
Creation of electron-positron pair transfers energy from background field (at interaction point)
χ 1 photon energy split evenly between electron and positron
For χ 1 most goes to one of the electron and positron
Coupling sfQED and classical processes
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
For χ 1 quantum depletion m vs classical a0
2m
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Laser absorption is increased (classically) because QED processes introduce new currents
Beyond the background field approximation
Depletion
In QED need to calculate transition rates between initial and final states that contain different numbers of photons
Does the LCFA let us take a simpler approach to calculating the effect of a QED avalanche on the background field
Beyond the background field approximation
Depletion
When does the quantum depletion have a serious effect on the background
Seipt et al PRL 118 154803 2017 for electron-beam laser collision need 10nC and a0 of 1000
Effects on angular distribution at lower intensity
Beyond the background field approximation
Depletion
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Positron production
Test bed
Electron-positron pair creation by the collision of high-energy particles with an intense laser pulse
eg wakefield accelerated electrons bremsstrahlung created gamma rayshellip
In the highly non-linear regime
Positron production
Test bed
Interaction can be modelled directly from QED (Di Piazza PRL 117 213201 2016)
Integrated full-scale QED-PIC simulations for wakefield acceleration plus photon and pair creation (Lobet et al PRAB 20 043401 2017)
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
We can handle divergent series using Borel summation
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Use the integral definition of a factorial
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Use the integral definition of a factorial
Swap the summation and integration
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
If they dont the integrand has a pole on the real axis
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
If they dont the integrand has a pole on the real axis
This has physicalsignificance
Beyond perturbative QED
Perturbation theory in quantum mechanics
Recall the dispersion relation for an EM wave in a warm plasma
The permittivity has a pole where the phase velocity of the wave and the particle velocity are equal
Gives rise to Landau damping
This has physicalsignificance
Beyond perturbative QED
Perturbation theory in quantum mechanics
If the terms do not alternate in sign Borel summation gives you an imaginary term that is non-perturbative in the coupling strength
Non-perturbative in the sense that exp(-1x) has Taylor expansion about 0 that is 0 to all orders
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Divergent perturbative series with coefficients that do not alternate in sign
Zeeman effect Coulomb potential perturbed by static magnetic field
Divergent perturbative series with coefficients alternating in sign
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Ionization rate
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative Why perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Does the same occur in quantum field theory
After all perturbation theory has proved extraordinarily successful
Beyond perturbative QED
Perturbation theory in quantum mechanics
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
S has a non-perturbative imaginary part
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
The action for a static electric field acquires an imaginary part that is non-perturbative in the electric field strength
Stark effect = ionisation rate Here we get the pair-creation rate from the vacuum
Ecrit = 13times1018 Vm
Beyond perturbative QED
Perturbation theory in QED
How do we access fields of this magnitude in the lab
Important parameter is χ (ratio of electric field in electron rest frame to the critical field of QED)
Beyond perturbative QED
QED in intense fields
χ = 1 means the electron sees in its rest frame a field strong enough for non-perturbative effects to dominate
Low order terms are suppressed only high order terms (ie involving large numbers of background photons) contribute
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
What about arbitrary field structures
Beyond perturbative QED
QED in intense fields
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
What do we lose by doing this
Harmonics sub-harmonics interference resonanceshellip
When is it acceptable to do so
How much bigger than 1 must a0 be
Coupling sfQED and classical processes
Locally constant field approximation
Other constraints on PIC simulations
Size of timestep must be set to avoid multiple scatterings (constraint set by rate of photon emission is strongest)
C P Ridgers et al J Comp Phys 260 273 (2014)
The rates (not cross-sections) for photon and pair production are calculated in an equivalent system of fields with the same instantaneous value of χ
eg a static magnetic field in the ultrarelativistic limit T Erber Rev Mod Phys 38 626 (1966)
Coupling sfQED and classical processes
PIC + Monte Carlo
We assumed a classical background field
Contains sufficient energy that the field is not affected by a (single) QED process
Energy is absorbed by plasmas ndash what happens to the background field
Coupling sfQED and classical processes
QED in intense fields
Creation of electron-positron pair transfers energy from background field (at interaction point)
χ 1 photon energy split evenly between electron and positron
For χ 1 most goes to one of the electron and positron
Coupling sfQED and classical processes
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
For χ 1 quantum depletion m vs classical a0
2m
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Laser absorption is increased (classically) because QED processes introduce new currents
Beyond the background field approximation
Depletion
In QED need to calculate transition rates between initial and final states that contain different numbers of photons
Does the LCFA let us take a simpler approach to calculating the effect of a QED avalanche on the background field
Beyond the background field approximation
Depletion
When does the quantum depletion have a serious effect on the background
Seipt et al PRL 118 154803 2017 for electron-beam laser collision need 10nC and a0 of 1000
Effects on angular distribution at lower intensity
Beyond the background field approximation
Depletion
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Positron production
Test bed
Electron-positron pair creation by the collision of high-energy particles with an intense laser pulse
eg wakefield accelerated electrons bremsstrahlung created gamma rayshellip
In the highly non-linear regime
Positron production
Test bed
Interaction can be modelled directly from QED (Di Piazza PRL 117 213201 2016)
Integrated full-scale QED-PIC simulations for wakefield acceleration plus photon and pair creation (Lobet et al PRAB 20 043401 2017)
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
We can handle divergent series using Borel summation
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Use the integral definition of a factorial
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Use the integral definition of a factorial
Swap the summation and integration
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
If they dont the integrand has a pole on the real axis
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
If they dont the integrand has a pole on the real axis
This has physicalsignificance
Beyond perturbative QED
Perturbation theory in quantum mechanics
Recall the dispersion relation for an EM wave in a warm plasma
The permittivity has a pole where the phase velocity of the wave and the particle velocity are equal
Gives rise to Landau damping
This has physicalsignificance
Beyond perturbative QED
Perturbation theory in quantum mechanics
If the terms do not alternate in sign Borel summation gives you an imaginary term that is non-perturbative in the coupling strength
Non-perturbative in the sense that exp(-1x) has Taylor expansion about 0 that is 0 to all orders
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Divergent perturbative series with coefficients that do not alternate in sign
Zeeman effect Coulomb potential perturbed by static magnetic field
Divergent perturbative series with coefficients alternating in sign
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Ionization rate
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative Why perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Does the same occur in quantum field theory
After all perturbation theory has proved extraordinarily successful
Beyond perturbative QED
Perturbation theory in quantum mechanics
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
S has a non-perturbative imaginary part
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
The action for a static electric field acquires an imaginary part that is non-perturbative in the electric field strength
Stark effect = ionisation rate Here we get the pair-creation rate from the vacuum
Ecrit = 13times1018 Vm
Beyond perturbative QED
Perturbation theory in QED
How do we access fields of this magnitude in the lab
Important parameter is χ (ratio of electric field in electron rest frame to the critical field of QED)
Beyond perturbative QED
QED in intense fields
χ = 1 means the electron sees in its rest frame a field strong enough for non-perturbative effects to dominate
Low order terms are suppressed only high order terms (ie involving large numbers of background photons) contribute
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
What about arbitrary field structures
Beyond perturbative QED
QED in intense fields
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
What do we lose by doing this
Harmonics sub-harmonics interference resonanceshellip
When is it acceptable to do so
How much bigger than 1 must a0 be
Coupling sfQED and classical processes
Locally constant field approximation
Other constraints on PIC simulations
Size of timestep must be set to avoid multiple scatterings (constraint set by rate of photon emission is strongest)
C P Ridgers et al J Comp Phys 260 273 (2014)
The rates (not cross-sections) for photon and pair production are calculated in an equivalent system of fields with the same instantaneous value of χ
eg a static magnetic field in the ultrarelativistic limit T Erber Rev Mod Phys 38 626 (1966)
Coupling sfQED and classical processes
PIC + Monte Carlo
We assumed a classical background field
Contains sufficient energy that the field is not affected by a (single) QED process
Energy is absorbed by plasmas ndash what happens to the background field
Coupling sfQED and classical processes
QED in intense fields
Creation of electron-positron pair transfers energy from background field (at interaction point)
χ 1 photon energy split evenly between electron and positron
For χ 1 most goes to one of the electron and positron
Coupling sfQED and classical processes
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
For χ 1 quantum depletion m vs classical a0
2m
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Laser absorption is increased (classically) because QED processes introduce new currents
Beyond the background field approximation
Depletion
In QED need to calculate transition rates between initial and final states that contain different numbers of photons
Does the LCFA let us take a simpler approach to calculating the effect of a QED avalanche on the background field
Beyond the background field approximation
Depletion
When does the quantum depletion have a serious effect on the background
Seipt et al PRL 118 154803 2017 for electron-beam laser collision need 10nC and a0 of 1000
Effects on angular distribution at lower intensity
Beyond the background field approximation
Depletion
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Positron production
Test bed
Electron-positron pair creation by the collision of high-energy particles with an intense laser pulse
eg wakefield accelerated electrons bremsstrahlung created gamma rayshellip
In the highly non-linear regime
Positron production
Test bed
Interaction can be modelled directly from QED (Di Piazza PRL 117 213201 2016)
Integrated full-scale QED-PIC simulations for wakefield acceleration plus photon and pair creation (Lobet et al PRAB 20 043401 2017)
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
We can handle divergent series using Borel summation
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Use the integral definition of a factorial
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Use the integral definition of a factorial
Swap the summation and integration
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
If they dont the integrand has a pole on the real axis
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
If they dont the integrand has a pole on the real axis
This has physicalsignificance
Beyond perturbative QED
Perturbation theory in quantum mechanics
Recall the dispersion relation for an EM wave in a warm plasma
The permittivity has a pole where the phase velocity of the wave and the particle velocity are equal
Gives rise to Landau damping
This has physicalsignificance
Beyond perturbative QED
Perturbation theory in quantum mechanics
If the terms do not alternate in sign Borel summation gives you an imaginary term that is non-perturbative in the coupling strength
Non-perturbative in the sense that exp(-1x) has Taylor expansion about 0 that is 0 to all orders
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Divergent perturbative series with coefficients that do not alternate in sign
Zeeman effect Coulomb potential perturbed by static magnetic field
Divergent perturbative series with coefficients alternating in sign
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Ionization rate
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative Why perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Does the same occur in quantum field theory
After all perturbation theory has proved extraordinarily successful
Beyond perturbative QED
Perturbation theory in quantum mechanics
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
S has a non-perturbative imaginary part
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
The action for a static electric field acquires an imaginary part that is non-perturbative in the electric field strength
Stark effect = ionisation rate Here we get the pair-creation rate from the vacuum
Ecrit = 13times1018 Vm
Beyond perturbative QED
Perturbation theory in QED
How do we access fields of this magnitude in the lab
Important parameter is χ (ratio of electric field in electron rest frame to the critical field of QED)
Beyond perturbative QED
QED in intense fields
χ = 1 means the electron sees in its rest frame a field strong enough for non-perturbative effects to dominate
Low order terms are suppressed only high order terms (ie involving large numbers of background photons) contribute
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
What about arbitrary field structures
Beyond perturbative QED
QED in intense fields
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
What do we lose by doing this
Harmonics sub-harmonics interference resonanceshellip
When is it acceptable to do so
How much bigger than 1 must a0 be
Coupling sfQED and classical processes
Locally constant field approximation
Other constraints on PIC simulations
Size of timestep must be set to avoid multiple scatterings (constraint set by rate of photon emission is strongest)
C P Ridgers et al J Comp Phys 260 273 (2014)
The rates (not cross-sections) for photon and pair production are calculated in an equivalent system of fields with the same instantaneous value of χ
eg a static magnetic field in the ultrarelativistic limit T Erber Rev Mod Phys 38 626 (1966)
Coupling sfQED and classical processes
PIC + Monte Carlo
We assumed a classical background field
Contains sufficient energy that the field is not affected by a (single) QED process
Energy is absorbed by plasmas ndash what happens to the background field
Coupling sfQED and classical processes
QED in intense fields
Creation of electron-positron pair transfers energy from background field (at interaction point)
χ 1 photon energy split evenly between electron and positron
For χ 1 most goes to one of the electron and positron
Coupling sfQED and classical processes
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
For χ 1 quantum depletion m vs classical a0
2m
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Laser absorption is increased (classically) because QED processes introduce new currents
Beyond the background field approximation
Depletion
In QED need to calculate transition rates between initial and final states that contain different numbers of photons
Does the LCFA let us take a simpler approach to calculating the effect of a QED avalanche on the background field
Beyond the background field approximation
Depletion
When does the quantum depletion have a serious effect on the background
Seipt et al PRL 118 154803 2017 for electron-beam laser collision need 10nC and a0 of 1000
Effects on angular distribution at lower intensity
Beyond the background field approximation
Depletion
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Positron production
Test bed
Electron-positron pair creation by the collision of high-energy particles with an intense laser pulse
eg wakefield accelerated electrons bremsstrahlung created gamma rayshellip
In the highly non-linear regime
Positron production
Test bed
Interaction can be modelled directly from QED (Di Piazza PRL 117 213201 2016)
Integrated full-scale QED-PIC simulations for wakefield acceleration plus photon and pair creation (Lobet et al PRAB 20 043401 2017)
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
We can handle divergent series using Borel summation
Use the integral definition of a factorial
Beyond perturbative QED
Perturbation theory in quantum mechanics
We can handle divergent series using Borel summation
Use the integral definition of a factorial
Swap the summation and integration
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
If they dont the integrand has a pole on the real axis
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
If they dont the integrand has a pole on the real axis
This has physicalsignificance
Beyond perturbative QED
Perturbation theory in quantum mechanics
Recall the dispersion relation for an EM wave in a warm plasma
The permittivity has a pole where the phase velocity of the wave and the particle velocity are equal
Gives rise to Landau damping
This has physicalsignificance
Beyond perturbative QED
Perturbation theory in quantum mechanics
If the terms do not alternate in sign Borel summation gives you an imaginary term that is non-perturbative in the coupling strength
Non-perturbative in the sense that exp(-1x) has Taylor expansion about 0 that is 0 to all orders
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Divergent perturbative series with coefficients that do not alternate in sign
Zeeman effect Coulomb potential perturbed by static magnetic field
Divergent perturbative series with coefficients alternating in sign
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Ionization rate
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative Why perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Does the same occur in quantum field theory
After all perturbation theory has proved extraordinarily successful
Beyond perturbative QED
Perturbation theory in quantum mechanics
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
S has a non-perturbative imaginary part
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
The action for a static electric field acquires an imaginary part that is non-perturbative in the electric field strength
Stark effect = ionisation rate Here we get the pair-creation rate from the vacuum
Ecrit = 13times1018 Vm
Beyond perturbative QED
Perturbation theory in QED
How do we access fields of this magnitude in the lab
Important parameter is χ (ratio of electric field in electron rest frame to the critical field of QED)
Beyond perturbative QED
QED in intense fields
χ = 1 means the electron sees in its rest frame a field strong enough for non-perturbative effects to dominate
Low order terms are suppressed only high order terms (ie involving large numbers of background photons) contribute
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
What about arbitrary field structures
Beyond perturbative QED
QED in intense fields
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
What do we lose by doing this
Harmonics sub-harmonics interference resonanceshellip
When is it acceptable to do so
How much bigger than 1 must a0 be
Coupling sfQED and classical processes
Locally constant field approximation
Other constraints on PIC simulations
Size of timestep must be set to avoid multiple scatterings (constraint set by rate of photon emission is strongest)
C P Ridgers et al J Comp Phys 260 273 (2014)
The rates (not cross-sections) for photon and pair production are calculated in an equivalent system of fields with the same instantaneous value of χ
eg a static magnetic field in the ultrarelativistic limit T Erber Rev Mod Phys 38 626 (1966)
Coupling sfQED and classical processes
PIC + Monte Carlo
We assumed a classical background field
Contains sufficient energy that the field is not affected by a (single) QED process
Energy is absorbed by plasmas ndash what happens to the background field
Coupling sfQED and classical processes
QED in intense fields
Creation of electron-positron pair transfers energy from background field (at interaction point)
χ 1 photon energy split evenly between electron and positron
For χ 1 most goes to one of the electron and positron
Coupling sfQED and classical processes
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
For χ 1 quantum depletion m vs classical a0
2m
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Laser absorption is increased (classically) because QED processes introduce new currents
Beyond the background field approximation
Depletion
In QED need to calculate transition rates between initial and final states that contain different numbers of photons
Does the LCFA let us take a simpler approach to calculating the effect of a QED avalanche on the background field
Beyond the background field approximation
Depletion
When does the quantum depletion have a serious effect on the background
Seipt et al PRL 118 154803 2017 for electron-beam laser collision need 10nC and a0 of 1000
Effects on angular distribution at lower intensity
Beyond the background field approximation
Depletion
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Positron production
Test bed
Electron-positron pair creation by the collision of high-energy particles with an intense laser pulse
eg wakefield accelerated electrons bremsstrahlung created gamma rayshellip
In the highly non-linear regime
Positron production
Test bed
Interaction can be modelled directly from QED (Di Piazza PRL 117 213201 2016)
Integrated full-scale QED-PIC simulations for wakefield acceleration plus photon and pair creation (Lobet et al PRAB 20 043401 2017)
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
We can handle divergent series using Borel summation
Use the integral definition of a factorial
Swap the summation and integration
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
If they dont the integrand has a pole on the real axis
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
If they dont the integrand has a pole on the real axis
This has physicalsignificance
Beyond perturbative QED
Perturbation theory in quantum mechanics
Recall the dispersion relation for an EM wave in a warm plasma
The permittivity has a pole where the phase velocity of the wave and the particle velocity are equal
Gives rise to Landau damping
This has physicalsignificance
Beyond perturbative QED
Perturbation theory in quantum mechanics
If the terms do not alternate in sign Borel summation gives you an imaginary term that is non-perturbative in the coupling strength
Non-perturbative in the sense that exp(-1x) has Taylor expansion about 0 that is 0 to all orders
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Divergent perturbative series with coefficients that do not alternate in sign
Zeeman effect Coulomb potential perturbed by static magnetic field
Divergent perturbative series with coefficients alternating in sign
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Ionization rate
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative Why perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Does the same occur in quantum field theory
After all perturbation theory has proved extraordinarily successful
Beyond perturbative QED
Perturbation theory in quantum mechanics
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
S has a non-perturbative imaginary part
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
The action for a static electric field acquires an imaginary part that is non-perturbative in the electric field strength
Stark effect = ionisation rate Here we get the pair-creation rate from the vacuum
Ecrit = 13times1018 Vm
Beyond perturbative QED
Perturbation theory in QED
How do we access fields of this magnitude in the lab
Important parameter is χ (ratio of electric field in electron rest frame to the critical field of QED)
Beyond perturbative QED
QED in intense fields
χ = 1 means the electron sees in its rest frame a field strong enough for non-perturbative effects to dominate
Low order terms are suppressed only high order terms (ie involving large numbers of background photons) contribute
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
What about arbitrary field structures
Beyond perturbative QED
QED in intense fields
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
What do we lose by doing this
Harmonics sub-harmonics interference resonanceshellip
When is it acceptable to do so
How much bigger than 1 must a0 be
Coupling sfQED and classical processes
Locally constant field approximation
Other constraints on PIC simulations
Size of timestep must be set to avoid multiple scatterings (constraint set by rate of photon emission is strongest)
C P Ridgers et al J Comp Phys 260 273 (2014)
The rates (not cross-sections) for photon and pair production are calculated in an equivalent system of fields with the same instantaneous value of χ
eg a static magnetic field in the ultrarelativistic limit T Erber Rev Mod Phys 38 626 (1966)
Coupling sfQED and classical processes
PIC + Monte Carlo
We assumed a classical background field
Contains sufficient energy that the field is not affected by a (single) QED process
Energy is absorbed by plasmas ndash what happens to the background field
Coupling sfQED and classical processes
QED in intense fields
Creation of electron-positron pair transfers energy from background field (at interaction point)
χ 1 photon energy split evenly between electron and positron
For χ 1 most goes to one of the electron and positron
Coupling sfQED and classical processes
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
For χ 1 quantum depletion m vs classical a0
2m
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Laser absorption is increased (classically) because QED processes introduce new currents
Beyond the background field approximation
Depletion
In QED need to calculate transition rates between initial and final states that contain different numbers of photons
Does the LCFA let us take a simpler approach to calculating the effect of a QED avalanche on the background field
Beyond the background field approximation
Depletion
When does the quantum depletion have a serious effect on the background
Seipt et al PRL 118 154803 2017 for electron-beam laser collision need 10nC and a0 of 1000
Effects on angular distribution at lower intensity
Beyond the background field approximation
Depletion
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Positron production
Test bed
Electron-positron pair creation by the collision of high-energy particles with an intense laser pulse
eg wakefield accelerated electrons bremsstrahlung created gamma rayshellip
In the highly non-linear regime
Positron production
Test bed
Interaction can be modelled directly from QED (Di Piazza PRL 117 213201 2016)
Integrated full-scale QED-PIC simulations for wakefield acceleration plus photon and pair creation (Lobet et al PRAB 20 043401 2017)
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
What does this mean for factorially-divergent series
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
If they dont the integrand has a pole on the real axis
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
If they dont the integrand has a pole on the real axis
This has physicalsignificance
Beyond perturbative QED
Perturbation theory in quantum mechanics
Recall the dispersion relation for an EM wave in a warm plasma
The permittivity has a pole where the phase velocity of the wave and the particle velocity are equal
Gives rise to Landau damping
This has physicalsignificance
Beyond perturbative QED
Perturbation theory in quantum mechanics
If the terms do not alternate in sign Borel summation gives you an imaginary term that is non-perturbative in the coupling strength
Non-perturbative in the sense that exp(-1x) has Taylor expansion about 0 that is 0 to all orders
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Divergent perturbative series with coefficients that do not alternate in sign
Zeeman effect Coulomb potential perturbed by static magnetic field
Divergent perturbative series with coefficients alternating in sign
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Ionization rate
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative Why perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Does the same occur in quantum field theory
After all perturbation theory has proved extraordinarily successful
Beyond perturbative QED
Perturbation theory in quantum mechanics
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
S has a non-perturbative imaginary part
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
The action for a static electric field acquires an imaginary part that is non-perturbative in the electric field strength
Stark effect = ionisation rate Here we get the pair-creation rate from the vacuum
Ecrit = 13times1018 Vm
Beyond perturbative QED
Perturbation theory in QED
How do we access fields of this magnitude in the lab
Important parameter is χ (ratio of electric field in electron rest frame to the critical field of QED)
Beyond perturbative QED
QED in intense fields
χ = 1 means the electron sees in its rest frame a field strong enough for non-perturbative effects to dominate
Low order terms are suppressed only high order terms (ie involving large numbers of background photons) contribute
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
What about arbitrary field structures
Beyond perturbative QED
QED in intense fields
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
What do we lose by doing this
Harmonics sub-harmonics interference resonanceshellip
When is it acceptable to do so
How much bigger than 1 must a0 be
Coupling sfQED and classical processes
Locally constant field approximation
Other constraints on PIC simulations
Size of timestep must be set to avoid multiple scatterings (constraint set by rate of photon emission is strongest)
C P Ridgers et al J Comp Phys 260 273 (2014)
The rates (not cross-sections) for photon and pair production are calculated in an equivalent system of fields with the same instantaneous value of χ
eg a static magnetic field in the ultrarelativistic limit T Erber Rev Mod Phys 38 626 (1966)
Coupling sfQED and classical processes
PIC + Monte Carlo
We assumed a classical background field
Contains sufficient energy that the field is not affected by a (single) QED process
Energy is absorbed by plasmas ndash what happens to the background field
Coupling sfQED and classical processes
QED in intense fields
Creation of electron-positron pair transfers energy from background field (at interaction point)
χ 1 photon energy split evenly between electron and positron
For χ 1 most goes to one of the electron and positron
Coupling sfQED and classical processes
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
For χ 1 quantum depletion m vs classical a0
2m
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Laser absorption is increased (classically) because QED processes introduce new currents
Beyond the background field approximation
Depletion
In QED need to calculate transition rates between initial and final states that contain different numbers of photons
Does the LCFA let us take a simpler approach to calculating the effect of a QED avalanche on the background field
Beyond the background field approximation
Depletion
When does the quantum depletion have a serious effect on the background
Seipt et al PRL 118 154803 2017 for electron-beam laser collision need 10nC and a0 of 1000
Effects on angular distribution at lower intensity
Beyond the background field approximation
Depletion
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Positron production
Test bed
Electron-positron pair creation by the collision of high-energy particles with an intense laser pulse
eg wakefield accelerated electrons bremsstrahlung created gamma rayshellip
In the highly non-linear regime
Positron production
Test bed
Interaction can be modelled directly from QED (Di Piazza PRL 117 213201 2016)
Integrated full-scale QED-PIC simulations for wakefield acceleration plus photon and pair creation (Lobet et al PRAB 20 043401 2017)
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
If they dont the integrand has a pole on the real axis
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
If they dont the integrand has a pole on the real axis
This has physicalsignificance
Beyond perturbative QED
Perturbation theory in quantum mechanics
Recall the dispersion relation for an EM wave in a warm plasma
The permittivity has a pole where the phase velocity of the wave and the particle velocity are equal
Gives rise to Landau damping
This has physicalsignificance
Beyond perturbative QED
Perturbation theory in quantum mechanics
If the terms do not alternate in sign Borel summation gives you an imaginary term that is non-perturbative in the coupling strength
Non-perturbative in the sense that exp(-1x) has Taylor expansion about 0 that is 0 to all orders
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Divergent perturbative series with coefficients that do not alternate in sign
Zeeman effect Coulomb potential perturbed by static magnetic field
Divergent perturbative series with coefficients alternating in sign
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Ionization rate
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative Why perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Does the same occur in quantum field theory
After all perturbation theory has proved extraordinarily successful
Beyond perturbative QED
Perturbation theory in quantum mechanics
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
S has a non-perturbative imaginary part
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
The action for a static electric field acquires an imaginary part that is non-perturbative in the electric field strength
Stark effect = ionisation rate Here we get the pair-creation rate from the vacuum
Ecrit = 13times1018 Vm
Beyond perturbative QED
Perturbation theory in QED
How do we access fields of this magnitude in the lab
Important parameter is χ (ratio of electric field in electron rest frame to the critical field of QED)
Beyond perturbative QED
QED in intense fields
χ = 1 means the electron sees in its rest frame a field strong enough for non-perturbative effects to dominate
Low order terms are suppressed only high order terms (ie involving large numbers of background photons) contribute
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
What about arbitrary field structures
Beyond perturbative QED
QED in intense fields
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
What do we lose by doing this
Harmonics sub-harmonics interference resonanceshellip
When is it acceptable to do so
How much bigger than 1 must a0 be
Coupling sfQED and classical processes
Locally constant field approximation
Other constraints on PIC simulations
Size of timestep must be set to avoid multiple scatterings (constraint set by rate of photon emission is strongest)
C P Ridgers et al J Comp Phys 260 273 (2014)
The rates (not cross-sections) for photon and pair production are calculated in an equivalent system of fields with the same instantaneous value of χ
eg a static magnetic field in the ultrarelativistic limit T Erber Rev Mod Phys 38 626 (1966)
Coupling sfQED and classical processes
PIC + Monte Carlo
We assumed a classical background field
Contains sufficient energy that the field is not affected by a (single) QED process
Energy is absorbed by plasmas ndash what happens to the background field
Coupling sfQED and classical processes
QED in intense fields
Creation of electron-positron pair transfers energy from background field (at interaction point)
χ 1 photon energy split evenly between electron and positron
For χ 1 most goes to one of the electron and positron
Coupling sfQED and classical processes
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
For χ 1 quantum depletion m vs classical a0
2m
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Laser absorption is increased (classically) because QED processes introduce new currents
Beyond the background field approximation
Depletion
In QED need to calculate transition rates between initial and final states that contain different numbers of photons
Does the LCFA let us take a simpler approach to calculating the effect of a QED avalanche on the background field
Beyond the background field approximation
Depletion
When does the quantum depletion have a serious effect on the background
Seipt et al PRL 118 154803 2017 for electron-beam laser collision need 10nC and a0 of 1000
Effects on angular distribution at lower intensity
Beyond the background field approximation
Depletion
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Positron production
Test bed
Electron-positron pair creation by the collision of high-energy particles with an intense laser pulse
eg wakefield accelerated electrons bremsstrahlung created gamma rayshellip
In the highly non-linear regime
Positron production
Test bed
Interaction can be modelled directly from QED (Di Piazza PRL 117 213201 2016)
Integrated full-scale QED-PIC simulations for wakefield acceleration plus photon and pair creation (Lobet et al PRAB 20 043401 2017)
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
If they dont the integrand has a pole on the real axis
Beyond perturbative QED
Perturbation theory in quantum mechanics
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
If they dont the integrand has a pole on the real axis
This has physicalsignificance
Beyond perturbative QED
Perturbation theory in quantum mechanics
Recall the dispersion relation for an EM wave in a warm plasma
The permittivity has a pole where the phase velocity of the wave and the particle velocity are equal
Gives rise to Landau damping
This has physicalsignificance
Beyond perturbative QED
Perturbation theory in quantum mechanics
If the terms do not alternate in sign Borel summation gives you an imaginary term that is non-perturbative in the coupling strength
Non-perturbative in the sense that exp(-1x) has Taylor expansion about 0 that is 0 to all orders
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Divergent perturbative series with coefficients that do not alternate in sign
Zeeman effect Coulomb potential perturbed by static magnetic field
Divergent perturbative series with coefficients alternating in sign
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Ionization rate
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative Why perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Does the same occur in quantum field theory
After all perturbation theory has proved extraordinarily successful
Beyond perturbative QED
Perturbation theory in quantum mechanics
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
S has a non-perturbative imaginary part
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
The action for a static electric field acquires an imaginary part that is non-perturbative in the electric field strength
Stark effect = ionisation rate Here we get the pair-creation rate from the vacuum
Ecrit = 13times1018 Vm
Beyond perturbative QED
Perturbation theory in QED
How do we access fields of this magnitude in the lab
Important parameter is χ (ratio of electric field in electron rest frame to the critical field of QED)
Beyond perturbative QED
QED in intense fields
χ = 1 means the electron sees in its rest frame a field strong enough for non-perturbative effects to dominate
Low order terms are suppressed only high order terms (ie involving large numbers of background photons) contribute
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
What about arbitrary field structures
Beyond perturbative QED
QED in intense fields
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
What do we lose by doing this
Harmonics sub-harmonics interference resonanceshellip
When is it acceptable to do so
How much bigger than 1 must a0 be
Coupling sfQED and classical processes
Locally constant field approximation
Other constraints on PIC simulations
Size of timestep must be set to avoid multiple scatterings (constraint set by rate of photon emission is strongest)
C P Ridgers et al J Comp Phys 260 273 (2014)
The rates (not cross-sections) for photon and pair production are calculated in an equivalent system of fields with the same instantaneous value of χ
eg a static magnetic field in the ultrarelativistic limit T Erber Rev Mod Phys 38 626 (1966)
Coupling sfQED and classical processes
PIC + Monte Carlo
We assumed a classical background field
Contains sufficient energy that the field is not affected by a (single) QED process
Energy is absorbed by plasmas ndash what happens to the background field
Coupling sfQED and classical processes
QED in intense fields
Creation of electron-positron pair transfers energy from background field (at interaction point)
χ 1 photon energy split evenly between electron and positron
For χ 1 most goes to one of the electron and positron
Coupling sfQED and classical processes
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
For χ 1 quantum depletion m vs classical a0
2m
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Laser absorption is increased (classically) because QED processes introduce new currents
Beyond the background field approximation
Depletion
In QED need to calculate transition rates between initial and final states that contain different numbers of photons
Does the LCFA let us take a simpler approach to calculating the effect of a QED avalanche on the background field
Beyond the background field approximation
Depletion
When does the quantum depletion have a serious effect on the background
Seipt et al PRL 118 154803 2017 for electron-beam laser collision need 10nC and a0 of 1000
Effects on angular distribution at lower intensity
Beyond the background field approximation
Depletion
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Positron production
Test bed
Electron-positron pair creation by the collision of high-energy particles with an intense laser pulse
eg wakefield accelerated electrons bremsstrahlung created gamma rayshellip
In the highly non-linear regime
Positron production
Test bed
Interaction can be modelled directly from QED (Di Piazza PRL 117 213201 2016)
Integrated full-scale QED-PIC simulations for wakefield acceleration plus photon and pair creation (Lobet et al PRAB 20 043401 2017)
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
What does this mean for factorially-divergent series
If the terms alternate in sign the result is real and finite
If they dont the integrand has a pole on the real axis
This has physicalsignificance
Beyond perturbative QED
Perturbation theory in quantum mechanics
Recall the dispersion relation for an EM wave in a warm plasma
The permittivity has a pole where the phase velocity of the wave and the particle velocity are equal
Gives rise to Landau damping
This has physicalsignificance
Beyond perturbative QED
Perturbation theory in quantum mechanics
If the terms do not alternate in sign Borel summation gives you an imaginary term that is non-perturbative in the coupling strength
Non-perturbative in the sense that exp(-1x) has Taylor expansion about 0 that is 0 to all orders
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Divergent perturbative series with coefficients that do not alternate in sign
Zeeman effect Coulomb potential perturbed by static magnetic field
Divergent perturbative series with coefficients alternating in sign
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Ionization rate
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative Why perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Does the same occur in quantum field theory
After all perturbation theory has proved extraordinarily successful
Beyond perturbative QED
Perturbation theory in quantum mechanics
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
S has a non-perturbative imaginary part
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
The action for a static electric field acquires an imaginary part that is non-perturbative in the electric field strength
Stark effect = ionisation rate Here we get the pair-creation rate from the vacuum
Ecrit = 13times1018 Vm
Beyond perturbative QED
Perturbation theory in QED
How do we access fields of this magnitude in the lab
Important parameter is χ (ratio of electric field in electron rest frame to the critical field of QED)
Beyond perturbative QED
QED in intense fields
χ = 1 means the electron sees in its rest frame a field strong enough for non-perturbative effects to dominate
Low order terms are suppressed only high order terms (ie involving large numbers of background photons) contribute
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
What about arbitrary field structures
Beyond perturbative QED
QED in intense fields
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
What do we lose by doing this
Harmonics sub-harmonics interference resonanceshellip
When is it acceptable to do so
How much bigger than 1 must a0 be
Coupling sfQED and classical processes
Locally constant field approximation
Other constraints on PIC simulations
Size of timestep must be set to avoid multiple scatterings (constraint set by rate of photon emission is strongest)
C P Ridgers et al J Comp Phys 260 273 (2014)
The rates (not cross-sections) for photon and pair production are calculated in an equivalent system of fields with the same instantaneous value of χ
eg a static magnetic field in the ultrarelativistic limit T Erber Rev Mod Phys 38 626 (1966)
Coupling sfQED and classical processes
PIC + Monte Carlo
We assumed a classical background field
Contains sufficient energy that the field is not affected by a (single) QED process
Energy is absorbed by plasmas ndash what happens to the background field
Coupling sfQED and classical processes
QED in intense fields
Creation of electron-positron pair transfers energy from background field (at interaction point)
χ 1 photon energy split evenly between electron and positron
For χ 1 most goes to one of the electron and positron
Coupling sfQED and classical processes
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
For χ 1 quantum depletion m vs classical a0
2m
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Laser absorption is increased (classically) because QED processes introduce new currents
Beyond the background field approximation
Depletion
In QED need to calculate transition rates between initial and final states that contain different numbers of photons
Does the LCFA let us take a simpler approach to calculating the effect of a QED avalanche on the background field
Beyond the background field approximation
Depletion
When does the quantum depletion have a serious effect on the background
Seipt et al PRL 118 154803 2017 for electron-beam laser collision need 10nC and a0 of 1000
Effects on angular distribution at lower intensity
Beyond the background field approximation
Depletion
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Positron production
Test bed
Electron-positron pair creation by the collision of high-energy particles with an intense laser pulse
eg wakefield accelerated electrons bremsstrahlung created gamma rayshellip
In the highly non-linear regime
Positron production
Test bed
Interaction can be modelled directly from QED (Di Piazza PRL 117 213201 2016)
Integrated full-scale QED-PIC simulations for wakefield acceleration plus photon and pair creation (Lobet et al PRAB 20 043401 2017)
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
Recall the dispersion relation for an EM wave in a warm plasma
The permittivity has a pole where the phase velocity of the wave and the particle velocity are equal
Gives rise to Landau damping
This has physicalsignificance
Beyond perturbative QED
Perturbation theory in quantum mechanics
If the terms do not alternate in sign Borel summation gives you an imaginary term that is non-perturbative in the coupling strength
Non-perturbative in the sense that exp(-1x) has Taylor expansion about 0 that is 0 to all orders
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Divergent perturbative series with coefficients that do not alternate in sign
Zeeman effect Coulomb potential perturbed by static magnetic field
Divergent perturbative series with coefficients alternating in sign
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Ionization rate
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative Why perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Does the same occur in quantum field theory
After all perturbation theory has proved extraordinarily successful
Beyond perturbative QED
Perturbation theory in quantum mechanics
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
S has a non-perturbative imaginary part
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
The action for a static electric field acquires an imaginary part that is non-perturbative in the electric field strength
Stark effect = ionisation rate Here we get the pair-creation rate from the vacuum
Ecrit = 13times1018 Vm
Beyond perturbative QED
Perturbation theory in QED
How do we access fields of this magnitude in the lab
Important parameter is χ (ratio of electric field in electron rest frame to the critical field of QED)
Beyond perturbative QED
QED in intense fields
χ = 1 means the electron sees in its rest frame a field strong enough for non-perturbative effects to dominate
Low order terms are suppressed only high order terms (ie involving large numbers of background photons) contribute
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
What about arbitrary field structures
Beyond perturbative QED
QED in intense fields
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
What do we lose by doing this
Harmonics sub-harmonics interference resonanceshellip
When is it acceptable to do so
How much bigger than 1 must a0 be
Coupling sfQED and classical processes
Locally constant field approximation
Other constraints on PIC simulations
Size of timestep must be set to avoid multiple scatterings (constraint set by rate of photon emission is strongest)
C P Ridgers et al J Comp Phys 260 273 (2014)
The rates (not cross-sections) for photon and pair production are calculated in an equivalent system of fields with the same instantaneous value of χ
eg a static magnetic field in the ultrarelativistic limit T Erber Rev Mod Phys 38 626 (1966)
Coupling sfQED and classical processes
PIC + Monte Carlo
We assumed a classical background field
Contains sufficient energy that the field is not affected by a (single) QED process
Energy is absorbed by plasmas ndash what happens to the background field
Coupling sfQED and classical processes
QED in intense fields
Creation of electron-positron pair transfers energy from background field (at interaction point)
χ 1 photon energy split evenly between electron and positron
For χ 1 most goes to one of the electron and positron
Coupling sfQED and classical processes
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
For χ 1 quantum depletion m vs classical a0
2m
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Laser absorption is increased (classically) because QED processes introduce new currents
Beyond the background field approximation
Depletion
In QED need to calculate transition rates between initial and final states that contain different numbers of photons
Does the LCFA let us take a simpler approach to calculating the effect of a QED avalanche on the background field
Beyond the background field approximation
Depletion
When does the quantum depletion have a serious effect on the background
Seipt et al PRL 118 154803 2017 for electron-beam laser collision need 10nC and a0 of 1000
Effects on angular distribution at lower intensity
Beyond the background field approximation
Depletion
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Positron production
Test bed
Electron-positron pair creation by the collision of high-energy particles with an intense laser pulse
eg wakefield accelerated electrons bremsstrahlung created gamma rayshellip
In the highly non-linear regime
Positron production
Test bed
Interaction can be modelled directly from QED (Di Piazza PRL 117 213201 2016)
Integrated full-scale QED-PIC simulations for wakefield acceleration plus photon and pair creation (Lobet et al PRAB 20 043401 2017)
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
If the terms do not alternate in sign Borel summation gives you an imaginary term that is non-perturbative in the coupling strength
Non-perturbative in the sense that exp(-1x) has Taylor expansion about 0 that is 0 to all orders
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Divergent perturbative series with coefficients that do not alternate in sign
Zeeman effect Coulomb potential perturbed by static magnetic field
Divergent perturbative series with coefficients alternating in sign
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Ionization rate
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative Why perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Does the same occur in quantum field theory
After all perturbation theory has proved extraordinarily successful
Beyond perturbative QED
Perturbation theory in quantum mechanics
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
S has a non-perturbative imaginary part
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
The action for a static electric field acquires an imaginary part that is non-perturbative in the electric field strength
Stark effect = ionisation rate Here we get the pair-creation rate from the vacuum
Ecrit = 13times1018 Vm
Beyond perturbative QED
Perturbation theory in QED
How do we access fields of this magnitude in the lab
Important parameter is χ (ratio of electric field in electron rest frame to the critical field of QED)
Beyond perturbative QED
QED in intense fields
χ = 1 means the electron sees in its rest frame a field strong enough for non-perturbative effects to dominate
Low order terms are suppressed only high order terms (ie involving large numbers of background photons) contribute
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
What about arbitrary field structures
Beyond perturbative QED
QED in intense fields
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
What do we lose by doing this
Harmonics sub-harmonics interference resonanceshellip
When is it acceptable to do so
How much bigger than 1 must a0 be
Coupling sfQED and classical processes
Locally constant field approximation
Other constraints on PIC simulations
Size of timestep must be set to avoid multiple scatterings (constraint set by rate of photon emission is strongest)
C P Ridgers et al J Comp Phys 260 273 (2014)
The rates (not cross-sections) for photon and pair production are calculated in an equivalent system of fields with the same instantaneous value of χ
eg a static magnetic field in the ultrarelativistic limit T Erber Rev Mod Phys 38 626 (1966)
Coupling sfQED and classical processes
PIC + Monte Carlo
We assumed a classical background field
Contains sufficient energy that the field is not affected by a (single) QED process
Energy is absorbed by plasmas ndash what happens to the background field
Coupling sfQED and classical processes
QED in intense fields
Creation of electron-positron pair transfers energy from background field (at interaction point)
χ 1 photon energy split evenly between electron and positron
For χ 1 most goes to one of the electron and positron
Coupling sfQED and classical processes
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
For χ 1 quantum depletion m vs classical a0
2m
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Laser absorption is increased (classically) because QED processes introduce new currents
Beyond the background field approximation
Depletion
In QED need to calculate transition rates between initial and final states that contain different numbers of photons
Does the LCFA let us take a simpler approach to calculating the effect of a QED avalanche on the background field
Beyond the background field approximation
Depletion
When does the quantum depletion have a serious effect on the background
Seipt et al PRL 118 154803 2017 for electron-beam laser collision need 10nC and a0 of 1000
Effects on angular distribution at lower intensity
Beyond the background field approximation
Depletion
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Positron production
Test bed
Electron-positron pair creation by the collision of high-energy particles with an intense laser pulse
eg wakefield accelerated electrons bremsstrahlung created gamma rayshellip
In the highly non-linear regime
Positron production
Test bed
Interaction can be modelled directly from QED (Di Piazza PRL 117 213201 2016)
Integrated full-scale QED-PIC simulations for wakefield acceleration plus photon and pair creation (Lobet et al PRAB 20 043401 2017)
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
Stark effect Coulomb potential perturbed by static electric field
Divergent perturbative series with coefficients that do not alternate in sign
Zeeman effect Coulomb potential perturbed by static magnetic field
Divergent perturbative series with coefficients alternating in sign
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Ionization rate
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative Why perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Does the same occur in quantum field theory
After all perturbation theory has proved extraordinarily successful
Beyond perturbative QED
Perturbation theory in quantum mechanics
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
S has a non-perturbative imaginary part
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
The action for a static electric field acquires an imaginary part that is non-perturbative in the electric field strength
Stark effect = ionisation rate Here we get the pair-creation rate from the vacuum
Ecrit = 13times1018 Vm
Beyond perturbative QED
Perturbation theory in QED
How do we access fields of this magnitude in the lab
Important parameter is χ (ratio of electric field in electron rest frame to the critical field of QED)
Beyond perturbative QED
QED in intense fields
χ = 1 means the electron sees in its rest frame a field strong enough for non-perturbative effects to dominate
Low order terms are suppressed only high order terms (ie involving large numbers of background photons) contribute
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
What about arbitrary field structures
Beyond perturbative QED
QED in intense fields
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
What do we lose by doing this
Harmonics sub-harmonics interference resonanceshellip
When is it acceptable to do so
How much bigger than 1 must a0 be
Coupling sfQED and classical processes
Locally constant field approximation
Other constraints on PIC simulations
Size of timestep must be set to avoid multiple scatterings (constraint set by rate of photon emission is strongest)
C P Ridgers et al J Comp Phys 260 273 (2014)
The rates (not cross-sections) for photon and pair production are calculated in an equivalent system of fields with the same instantaneous value of χ
eg a static magnetic field in the ultrarelativistic limit T Erber Rev Mod Phys 38 626 (1966)
Coupling sfQED and classical processes
PIC + Monte Carlo
We assumed a classical background field
Contains sufficient energy that the field is not affected by a (single) QED process
Energy is absorbed by plasmas ndash what happens to the background field
Coupling sfQED and classical processes
QED in intense fields
Creation of electron-positron pair transfers energy from background field (at interaction point)
χ 1 photon energy split evenly between electron and positron
For χ 1 most goes to one of the electron and positron
Coupling sfQED and classical processes
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
For χ 1 quantum depletion m vs classical a0
2m
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Laser absorption is increased (classically) because QED processes introduce new currents
Beyond the background field approximation
Depletion
In QED need to calculate transition rates between initial and final states that contain different numbers of photons
Does the LCFA let us take a simpler approach to calculating the effect of a QED avalanche on the background field
Beyond the background field approximation
Depletion
When does the quantum depletion have a serious effect on the background
Seipt et al PRL 118 154803 2017 for electron-beam laser collision need 10nC and a0 of 1000
Effects on angular distribution at lower intensity
Beyond the background field approximation
Depletion
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Positron production
Test bed
Electron-positron pair creation by the collision of high-energy particles with an intense laser pulse
eg wakefield accelerated electrons bremsstrahlung created gamma rayshellip
In the highly non-linear regime
Positron production
Test bed
Interaction can be modelled directly from QED (Di Piazza PRL 117 213201 2016)
Integrated full-scale QED-PIC simulations for wakefield acceleration plus photon and pair creation (Lobet et al PRAB 20 043401 2017)
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Ionization rate
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative Why perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Does the same occur in quantum field theory
After all perturbation theory has proved extraordinarily successful
Beyond perturbative QED
Perturbation theory in quantum mechanics
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
S has a non-perturbative imaginary part
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
The action for a static electric field acquires an imaginary part that is non-perturbative in the electric field strength
Stark effect = ionisation rate Here we get the pair-creation rate from the vacuum
Ecrit = 13times1018 Vm
Beyond perturbative QED
Perturbation theory in QED
How do we access fields of this magnitude in the lab
Important parameter is χ (ratio of electric field in electron rest frame to the critical field of QED)
Beyond perturbative QED
QED in intense fields
χ = 1 means the electron sees in its rest frame a field strong enough for non-perturbative effects to dominate
Low order terms are suppressed only high order terms (ie involving large numbers of background photons) contribute
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
What about arbitrary field structures
Beyond perturbative QED
QED in intense fields
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
What do we lose by doing this
Harmonics sub-harmonics interference resonanceshellip
When is it acceptable to do so
How much bigger than 1 must a0 be
Coupling sfQED and classical processes
Locally constant field approximation
Other constraints on PIC simulations
Size of timestep must be set to avoid multiple scatterings (constraint set by rate of photon emission is strongest)
C P Ridgers et al J Comp Phys 260 273 (2014)
The rates (not cross-sections) for photon and pair production are calculated in an equivalent system of fields with the same instantaneous value of χ
eg a static magnetic field in the ultrarelativistic limit T Erber Rev Mod Phys 38 626 (1966)
Coupling sfQED and classical processes
PIC + Monte Carlo
We assumed a classical background field
Contains sufficient energy that the field is not affected by a (single) QED process
Energy is absorbed by plasmas ndash what happens to the background field
Coupling sfQED and classical processes
QED in intense fields
Creation of electron-positron pair transfers energy from background field (at interaction point)
χ 1 photon energy split evenly between electron and positron
For χ 1 most goes to one of the electron and positron
Coupling sfQED and classical processes
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
For χ 1 quantum depletion m vs classical a0
2m
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Laser absorption is increased (classically) because QED processes introduce new currents
Beyond the background field approximation
Depletion
In QED need to calculate transition rates between initial and final states that contain different numbers of photons
Does the LCFA let us take a simpler approach to calculating the effect of a QED avalanche on the background field
Beyond the background field approximation
Depletion
When does the quantum depletion have a serious effect on the background
Seipt et al PRL 118 154803 2017 for electron-beam laser collision need 10nC and a0 of 1000
Effects on angular distribution at lower intensity
Beyond the background field approximation
Depletion
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Positron production
Test bed
Electron-positron pair creation by the collision of high-energy particles with an intense laser pulse
eg wakefield accelerated electrons bremsstrahlung created gamma rayshellip
In the highly non-linear regime
Positron production
Test bed
Interaction can be modelled directly from QED (Di Piazza PRL 117 213201 2016)
Integrated full-scale QED-PIC simulations for wakefield acceleration plus photon and pair creation (Lobet et al PRAB 20 043401 2017)
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
Stark effect Coulomb potential perturbed by static electric field
Energy shift of the ground state of H
Ionization rate
Zeeman effect Coulomb potential perturbed by static magnetic field
Energy shift of the ground state of H
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative Why perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Does the same occur in quantum field theory
After all perturbation theory has proved extraordinarily successful
Beyond perturbative QED
Perturbation theory in quantum mechanics
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
S has a non-perturbative imaginary part
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
The action for a static electric field acquires an imaginary part that is non-perturbative in the electric field strength
Stark effect = ionisation rate Here we get the pair-creation rate from the vacuum
Ecrit = 13times1018 Vm
Beyond perturbative QED
Perturbation theory in QED
How do we access fields of this magnitude in the lab
Important parameter is χ (ratio of electric field in electron rest frame to the critical field of QED)
Beyond perturbative QED
QED in intense fields
χ = 1 means the electron sees in its rest frame a field strong enough for non-perturbative effects to dominate
Low order terms are suppressed only high order terms (ie involving large numbers of background photons) contribute
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
What about arbitrary field structures
Beyond perturbative QED
QED in intense fields
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
What do we lose by doing this
Harmonics sub-harmonics interference resonanceshellip
When is it acceptable to do so
How much bigger than 1 must a0 be
Coupling sfQED and classical processes
Locally constant field approximation
Other constraints on PIC simulations
Size of timestep must be set to avoid multiple scatterings (constraint set by rate of photon emission is strongest)
C P Ridgers et al J Comp Phys 260 273 (2014)
The rates (not cross-sections) for photon and pair production are calculated in an equivalent system of fields with the same instantaneous value of χ
eg a static magnetic field in the ultrarelativistic limit T Erber Rev Mod Phys 38 626 (1966)
Coupling sfQED and classical processes
PIC + Monte Carlo
We assumed a classical background field
Contains sufficient energy that the field is not affected by a (single) QED process
Energy is absorbed by plasmas ndash what happens to the background field
Coupling sfQED and classical processes
QED in intense fields
Creation of electron-positron pair transfers energy from background field (at interaction point)
χ 1 photon energy split evenly between electron and positron
For χ 1 most goes to one of the electron and positron
Coupling sfQED and classical processes
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
For χ 1 quantum depletion m vs classical a0
2m
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Laser absorption is increased (classically) because QED processes introduce new currents
Beyond the background field approximation
Depletion
In QED need to calculate transition rates between initial and final states that contain different numbers of photons
Does the LCFA let us take a simpler approach to calculating the effect of a QED avalanche on the background field
Beyond the background field approximation
Depletion
When does the quantum depletion have a serious effect on the background
Seipt et al PRL 118 154803 2017 for electron-beam laser collision need 10nC and a0 of 1000
Effects on angular distribution at lower intensity
Beyond the background field approximation
Depletion
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Positron production
Test bed
Electron-positron pair creation by the collision of high-energy particles with an intense laser pulse
eg wakefield accelerated electrons bremsstrahlung created gamma rayshellip
In the highly non-linear regime
Positron production
Test bed
Interaction can be modelled directly from QED (Di Piazza PRL 117 213201 2016)
Integrated full-scale QED-PIC simulations for wakefield acceleration plus photon and pair creation (Lobet et al PRAB 20 043401 2017)
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative Why perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Does the same occur in quantum field theory
After all perturbation theory has proved extraordinarily successful
Beyond perturbative QED
Perturbation theory in quantum mechanics
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
S has a non-perturbative imaginary part
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
The action for a static electric field acquires an imaginary part that is non-perturbative in the electric field strength
Stark effect = ionisation rate Here we get the pair-creation rate from the vacuum
Ecrit = 13times1018 Vm
Beyond perturbative QED
Perturbation theory in QED
How do we access fields of this magnitude in the lab
Important parameter is χ (ratio of electric field in electron rest frame to the critical field of QED)
Beyond perturbative QED
QED in intense fields
χ = 1 means the electron sees in its rest frame a field strong enough for non-perturbative effects to dominate
Low order terms are suppressed only high order terms (ie involving large numbers of background photons) contribute
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
What about arbitrary field structures
Beyond perturbative QED
QED in intense fields
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
What do we lose by doing this
Harmonics sub-harmonics interference resonanceshellip
When is it acceptable to do so
How much bigger than 1 must a0 be
Coupling sfQED and classical processes
Locally constant field approximation
Other constraints on PIC simulations
Size of timestep must be set to avoid multiple scatterings (constraint set by rate of photon emission is strongest)
C P Ridgers et al J Comp Phys 260 273 (2014)
The rates (not cross-sections) for photon and pair production are calculated in an equivalent system of fields with the same instantaneous value of χ
eg a static magnetic field in the ultrarelativistic limit T Erber Rev Mod Phys 38 626 (1966)
Coupling sfQED and classical processes
PIC + Monte Carlo
We assumed a classical background field
Contains sufficient energy that the field is not affected by a (single) QED process
Energy is absorbed by plasmas ndash what happens to the background field
Coupling sfQED and classical processes
QED in intense fields
Creation of electron-positron pair transfers energy from background field (at interaction point)
χ 1 photon energy split evenly between electron and positron
For χ 1 most goes to one of the electron and positron
Coupling sfQED and classical processes
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
For χ 1 quantum depletion m vs classical a0
2m
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Laser absorption is increased (classically) because QED processes introduce new currents
Beyond the background field approximation
Depletion
In QED need to calculate transition rates between initial and final states that contain different numbers of photons
Does the LCFA let us take a simpler approach to calculating the effect of a QED avalanche on the background field
Beyond the background field approximation
Depletion
When does the quantum depletion have a serious effect on the background
Seipt et al PRL 118 154803 2017 for electron-beam laser collision need 10nC and a0 of 1000
Effects on angular distribution at lower intensity
Beyond the background field approximation
Depletion
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Positron production
Test bed
Electron-positron pair creation by the collision of high-energy particles with an intense laser pulse
eg wakefield accelerated electrons bremsstrahlung created gamma rayshellip
In the highly non-linear regime
Positron production
Test bed
Interaction can be modelled directly from QED (Di Piazza PRL 117 213201 2016)
Integrated full-scale QED-PIC simulations for wakefield acceleration plus photon and pair creation (Lobet et al PRAB 20 043401 2017)
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
Perturbation theory is generically divergent
Controlling those divergences naturally introduces physics from the non-perturbative sector
Why non-perturbative Why perturbative
Beyond perturbative QED
Perturbation theory in quantum mechanics
Does the same occur in quantum field theory
After all perturbation theory has proved extraordinarily successful
Beyond perturbative QED
Perturbation theory in quantum mechanics
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
S has a non-perturbative imaginary part
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
The action for a static electric field acquires an imaginary part that is non-perturbative in the electric field strength
Stark effect = ionisation rate Here we get the pair-creation rate from the vacuum
Ecrit = 13times1018 Vm
Beyond perturbative QED
Perturbation theory in QED
How do we access fields of this magnitude in the lab
Important parameter is χ (ratio of electric field in electron rest frame to the critical field of QED)
Beyond perturbative QED
QED in intense fields
χ = 1 means the electron sees in its rest frame a field strong enough for non-perturbative effects to dominate
Low order terms are suppressed only high order terms (ie involving large numbers of background photons) contribute
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
What about arbitrary field structures
Beyond perturbative QED
QED in intense fields
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
What do we lose by doing this
Harmonics sub-harmonics interference resonanceshellip
When is it acceptable to do so
How much bigger than 1 must a0 be
Coupling sfQED and classical processes
Locally constant field approximation
Other constraints on PIC simulations
Size of timestep must be set to avoid multiple scatterings (constraint set by rate of photon emission is strongest)
C P Ridgers et al J Comp Phys 260 273 (2014)
The rates (not cross-sections) for photon and pair production are calculated in an equivalent system of fields with the same instantaneous value of χ
eg a static magnetic field in the ultrarelativistic limit T Erber Rev Mod Phys 38 626 (1966)
Coupling sfQED and classical processes
PIC + Monte Carlo
We assumed a classical background field
Contains sufficient energy that the field is not affected by a (single) QED process
Energy is absorbed by plasmas ndash what happens to the background field
Coupling sfQED and classical processes
QED in intense fields
Creation of electron-positron pair transfers energy from background field (at interaction point)
χ 1 photon energy split evenly between electron and positron
For χ 1 most goes to one of the electron and positron
Coupling sfQED and classical processes
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
For χ 1 quantum depletion m vs classical a0
2m
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Laser absorption is increased (classically) because QED processes introduce new currents
Beyond the background field approximation
Depletion
In QED need to calculate transition rates between initial and final states that contain different numbers of photons
Does the LCFA let us take a simpler approach to calculating the effect of a QED avalanche on the background field
Beyond the background field approximation
Depletion
When does the quantum depletion have a serious effect on the background
Seipt et al PRL 118 154803 2017 for electron-beam laser collision need 10nC and a0 of 1000
Effects on angular distribution at lower intensity
Beyond the background field approximation
Depletion
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Positron production
Test bed
Electron-positron pair creation by the collision of high-energy particles with an intense laser pulse
eg wakefield accelerated electrons bremsstrahlung created gamma rayshellip
In the highly non-linear regime
Positron production
Test bed
Interaction can be modelled directly from QED (Di Piazza PRL 117 213201 2016)
Integrated full-scale QED-PIC simulations for wakefield acceleration plus photon and pair creation (Lobet et al PRAB 20 043401 2017)
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
Does the same occur in quantum field theory
After all perturbation theory has proved extraordinarily successful
Beyond perturbative QED
Perturbation theory in quantum mechanics
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
S has a non-perturbative imaginary part
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
The action for a static electric field acquires an imaginary part that is non-perturbative in the electric field strength
Stark effect = ionisation rate Here we get the pair-creation rate from the vacuum
Ecrit = 13times1018 Vm
Beyond perturbative QED
Perturbation theory in QED
How do we access fields of this magnitude in the lab
Important parameter is χ (ratio of electric field in electron rest frame to the critical field of QED)
Beyond perturbative QED
QED in intense fields
χ = 1 means the electron sees in its rest frame a field strong enough for non-perturbative effects to dominate
Low order terms are suppressed only high order terms (ie involving large numbers of background photons) contribute
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
What about arbitrary field structures
Beyond perturbative QED
QED in intense fields
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
What do we lose by doing this
Harmonics sub-harmonics interference resonanceshellip
When is it acceptable to do so
How much bigger than 1 must a0 be
Coupling sfQED and classical processes
Locally constant field approximation
Other constraints on PIC simulations
Size of timestep must be set to avoid multiple scatterings (constraint set by rate of photon emission is strongest)
C P Ridgers et al J Comp Phys 260 273 (2014)
The rates (not cross-sections) for photon and pair production are calculated in an equivalent system of fields with the same instantaneous value of χ
eg a static magnetic field in the ultrarelativistic limit T Erber Rev Mod Phys 38 626 (1966)
Coupling sfQED and classical processes
PIC + Monte Carlo
We assumed a classical background field
Contains sufficient energy that the field is not affected by a (single) QED process
Energy is absorbed by plasmas ndash what happens to the background field
Coupling sfQED and classical processes
QED in intense fields
Creation of electron-positron pair transfers energy from background field (at interaction point)
χ 1 photon energy split evenly between electron and positron
For χ 1 most goes to one of the electron and positron
Coupling sfQED and classical processes
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
For χ 1 quantum depletion m vs classical a0
2m
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Laser absorption is increased (classically) because QED processes introduce new currents
Beyond the background field approximation
Depletion
In QED need to calculate transition rates between initial and final states that contain different numbers of photons
Does the LCFA let us take a simpler approach to calculating the effect of a QED avalanche on the background field
Beyond the background field approximation
Depletion
When does the quantum depletion have a serious effect on the background
Seipt et al PRL 118 154803 2017 for electron-beam laser collision need 10nC and a0 of 1000
Effects on angular distribution at lower intensity
Beyond the background field approximation
Depletion
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Positron production
Test bed
Electron-positron pair creation by the collision of high-energy particles with an intense laser pulse
eg wakefield accelerated electrons bremsstrahlung created gamma rayshellip
In the highly non-linear regime
Positron production
Test bed
Interaction can be modelled directly from QED (Di Piazza PRL 117 213201 2016)
Integrated full-scale QED-PIC simulations for wakefield acceleration plus photon and pair creation (Lobet et al PRAB 20 043401 2017)
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
S has a non-perturbative imaginary part
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
The action for a static electric field acquires an imaginary part that is non-perturbative in the electric field strength
Stark effect = ionisation rate Here we get the pair-creation rate from the vacuum
Ecrit = 13times1018 Vm
Beyond perturbative QED
Perturbation theory in QED
How do we access fields of this magnitude in the lab
Important parameter is χ (ratio of electric field in electron rest frame to the critical field of QED)
Beyond perturbative QED
QED in intense fields
χ = 1 means the electron sees in its rest frame a field strong enough for non-perturbative effects to dominate
Low order terms are suppressed only high order terms (ie involving large numbers of background photons) contribute
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
What about arbitrary field structures
Beyond perturbative QED
QED in intense fields
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
What do we lose by doing this
Harmonics sub-harmonics interference resonanceshellip
When is it acceptable to do so
How much bigger than 1 must a0 be
Coupling sfQED and classical processes
Locally constant field approximation
Other constraints on PIC simulations
Size of timestep must be set to avoid multiple scatterings (constraint set by rate of photon emission is strongest)
C P Ridgers et al J Comp Phys 260 273 (2014)
The rates (not cross-sections) for photon and pair production are calculated in an equivalent system of fields with the same instantaneous value of χ
eg a static magnetic field in the ultrarelativistic limit T Erber Rev Mod Phys 38 626 (1966)
Coupling sfQED and classical processes
PIC + Monte Carlo
We assumed a classical background field
Contains sufficient energy that the field is not affected by a (single) QED process
Energy is absorbed by plasmas ndash what happens to the background field
Coupling sfQED and classical processes
QED in intense fields
Creation of electron-positron pair transfers energy from background field (at interaction point)
χ 1 photon energy split evenly between electron and positron
For χ 1 most goes to one of the electron and positron
Coupling sfQED and classical processes
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
For χ 1 quantum depletion m vs classical a0
2m
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Laser absorption is increased (classically) because QED processes introduce new currents
Beyond the background field approximation
Depletion
In QED need to calculate transition rates between initial and final states that contain different numbers of photons
Does the LCFA let us take a simpler approach to calculating the effect of a QED avalanche on the background field
Beyond the background field approximation
Depletion
When does the quantum depletion have a serious effect on the background
Seipt et al PRL 118 154803 2017 for electron-beam laser collision need 10nC and a0 of 1000
Effects on angular distribution at lower intensity
Beyond the background field approximation
Depletion
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Positron production
Test bed
Electron-positron pair creation by the collision of high-energy particles with an intense laser pulse
eg wakefield accelerated electrons bremsstrahlung created gamma rayshellip
In the highly non-linear regime
Positron production
Test bed
Interaction can be modelled directly from QED (Di Piazza PRL 117 213201 2016)
Integrated full-scale QED-PIC simulations for wakefield acceleration plus photon and pair creation (Lobet et al PRAB 20 043401 2017)
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
Static magnetic field Euler-Heisenberg effective action (exact result)
Beyond perturbative QED
Perturbation theory in QED
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
S has a non-perturbative imaginary part
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
The action for a static electric field acquires an imaginary part that is non-perturbative in the electric field strength
Stark effect = ionisation rate Here we get the pair-creation rate from the vacuum
Ecrit = 13times1018 Vm
Beyond perturbative QED
Perturbation theory in QED
How do we access fields of this magnitude in the lab
Important parameter is χ (ratio of electric field in electron rest frame to the critical field of QED)
Beyond perturbative QED
QED in intense fields
χ = 1 means the electron sees in its rest frame a field strong enough for non-perturbative effects to dominate
Low order terms are suppressed only high order terms (ie involving large numbers of background photons) contribute
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
What about arbitrary field structures
Beyond perturbative QED
QED in intense fields
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
What do we lose by doing this
Harmonics sub-harmonics interference resonanceshellip
When is it acceptable to do so
How much bigger than 1 must a0 be
Coupling sfQED and classical processes
Locally constant field approximation
Other constraints on PIC simulations
Size of timestep must be set to avoid multiple scatterings (constraint set by rate of photon emission is strongest)
C P Ridgers et al J Comp Phys 260 273 (2014)
The rates (not cross-sections) for photon and pair production are calculated in an equivalent system of fields with the same instantaneous value of χ
eg a static magnetic field in the ultrarelativistic limit T Erber Rev Mod Phys 38 626 (1966)
Coupling sfQED and classical processes
PIC + Monte Carlo
We assumed a classical background field
Contains sufficient energy that the field is not affected by a (single) QED process
Energy is absorbed by plasmas ndash what happens to the background field
Coupling sfQED and classical processes
QED in intense fields
Creation of electron-positron pair transfers energy from background field (at interaction point)
χ 1 photon energy split evenly between electron and positron
For χ 1 most goes to one of the electron and positron
Coupling sfQED and classical processes
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
For χ 1 quantum depletion m vs classical a0
2m
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Laser absorption is increased (classically) because QED processes introduce new currents
Beyond the background field approximation
Depletion
In QED need to calculate transition rates between initial and final states that contain different numbers of photons
Does the LCFA let us take a simpler approach to calculating the effect of a QED avalanche on the background field
Beyond the background field approximation
Depletion
When does the quantum depletion have a serious effect on the background
Seipt et al PRL 118 154803 2017 for electron-beam laser collision need 10nC and a0 of 1000
Effects on angular distribution at lower intensity
Beyond the background field approximation
Depletion
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Positron production
Test bed
Electron-positron pair creation by the collision of high-energy particles with an intense laser pulse
eg wakefield accelerated electrons bremsstrahlung created gamma rayshellip
In the highly non-linear regime
Positron production
Test bed
Interaction can be modelled directly from QED (Di Piazza PRL 117 213201 2016)
Integrated full-scale QED-PIC simulations for wakefield acceleration plus photon and pair creation (Lobet et al PRAB 20 043401 2017)
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
S has a non-perturbative imaginary part
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
The action for a static electric field acquires an imaginary part that is non-perturbative in the electric field strength
Stark effect = ionisation rate Here we get the pair-creation rate from the vacuum
Ecrit = 13times1018 Vm
Beyond perturbative QED
Perturbation theory in QED
How do we access fields of this magnitude in the lab
Important parameter is χ (ratio of electric field in electron rest frame to the critical field of QED)
Beyond perturbative QED
QED in intense fields
χ = 1 means the electron sees in its rest frame a field strong enough for non-perturbative effects to dominate
Low order terms are suppressed only high order terms (ie involving large numbers of background photons) contribute
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
What about arbitrary field structures
Beyond perturbative QED
QED in intense fields
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
What do we lose by doing this
Harmonics sub-harmonics interference resonanceshellip
When is it acceptable to do so
How much bigger than 1 must a0 be
Coupling sfQED and classical processes
Locally constant field approximation
Other constraints on PIC simulations
Size of timestep must be set to avoid multiple scatterings (constraint set by rate of photon emission is strongest)
C P Ridgers et al J Comp Phys 260 273 (2014)
The rates (not cross-sections) for photon and pair production are calculated in an equivalent system of fields with the same instantaneous value of χ
eg a static magnetic field in the ultrarelativistic limit T Erber Rev Mod Phys 38 626 (1966)
Coupling sfQED and classical processes
PIC + Monte Carlo
We assumed a classical background field
Contains sufficient energy that the field is not affected by a (single) QED process
Energy is absorbed by plasmas ndash what happens to the background field
Coupling sfQED and classical processes
QED in intense fields
Creation of electron-positron pair transfers energy from background field (at interaction point)
χ 1 photon energy split evenly between electron and positron
For χ 1 most goes to one of the electron and positron
Coupling sfQED and classical processes
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
For χ 1 quantum depletion m vs classical a0
2m
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Laser absorption is increased (classically) because QED processes introduce new currents
Beyond the background field approximation
Depletion
In QED need to calculate transition rates between initial and final states that contain different numbers of photons
Does the LCFA let us take a simpler approach to calculating the effect of a QED avalanche on the background field
Beyond the background field approximation
Depletion
When does the quantum depletion have a serious effect on the background
Seipt et al PRL 118 154803 2017 for electron-beam laser collision need 10nC and a0 of 1000
Effects on angular distribution at lower intensity
Beyond the background field approximation
Depletion
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Positron production
Test bed
Electron-positron pair creation by the collision of high-energy particles with an intense laser pulse
eg wakefield accelerated electrons bremsstrahlung created gamma rayshellip
In the highly non-linear regime
Positron production
Test bed
Interaction can be modelled directly from QED (Di Piazza PRL 117 213201 2016)
Integrated full-scale QED-PIC simulations for wakefield acceleration plus photon and pair creation (Lobet et al PRAB 20 043401 2017)
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
Static electric field The field invariants are E2 ndash B2 and EB
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
S has a non-perturbative imaginary part
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
The action for a static electric field acquires an imaginary part that is non-perturbative in the electric field strength
Stark effect = ionisation rate Here we get the pair-creation rate from the vacuum
Ecrit = 13times1018 Vm
Beyond perturbative QED
Perturbation theory in QED
How do we access fields of this magnitude in the lab
Important parameter is χ (ratio of electric field in electron rest frame to the critical field of QED)
Beyond perturbative QED
QED in intense fields
χ = 1 means the electron sees in its rest frame a field strong enough for non-perturbative effects to dominate
Low order terms are suppressed only high order terms (ie involving large numbers of background photons) contribute
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
What about arbitrary field structures
Beyond perturbative QED
QED in intense fields
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
What do we lose by doing this
Harmonics sub-harmonics interference resonanceshellip
When is it acceptable to do so
How much bigger than 1 must a0 be
Coupling sfQED and classical processes
Locally constant field approximation
Other constraints on PIC simulations
Size of timestep must be set to avoid multiple scatterings (constraint set by rate of photon emission is strongest)
C P Ridgers et al J Comp Phys 260 273 (2014)
The rates (not cross-sections) for photon and pair production are calculated in an equivalent system of fields with the same instantaneous value of χ
eg a static magnetic field in the ultrarelativistic limit T Erber Rev Mod Phys 38 626 (1966)
Coupling sfQED and classical processes
PIC + Monte Carlo
We assumed a classical background field
Contains sufficient energy that the field is not affected by a (single) QED process
Energy is absorbed by plasmas ndash what happens to the background field
Coupling sfQED and classical processes
QED in intense fields
Creation of electron-positron pair transfers energy from background field (at interaction point)
χ 1 photon energy split evenly between electron and positron
For χ 1 most goes to one of the electron and positron
Coupling sfQED and classical processes
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
For χ 1 quantum depletion m vs classical a0
2m
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Laser absorption is increased (classically) because QED processes introduce new currents
Beyond the background field approximation
Depletion
In QED need to calculate transition rates between initial and final states that contain different numbers of photons
Does the LCFA let us take a simpler approach to calculating the effect of a QED avalanche on the background field
Beyond the background field approximation
Depletion
When does the quantum depletion have a serious effect on the background
Seipt et al PRL 118 154803 2017 for electron-beam laser collision need 10nC and a0 of 1000
Effects on angular distribution at lower intensity
Beyond the background field approximation
Depletion
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Positron production
Test bed
Electron-positron pair creation by the collision of high-energy particles with an intense laser pulse
eg wakefield accelerated electrons bremsstrahlung created gamma rayshellip
In the highly non-linear regime
Positron production
Test bed
Interaction can be modelled directly from QED (Di Piazza PRL 117 213201 2016)
Integrated full-scale QED-PIC simulations for wakefield acceleration plus photon and pair creation (Lobet et al PRAB 20 043401 2017)
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
S has a non-perturbative imaginary part
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
The action for a static electric field acquires an imaginary part that is non-perturbative in the electric field strength
Stark effect = ionisation rate Here we get the pair-creation rate from the vacuum
Ecrit = 13times1018 Vm
Beyond perturbative QED
Perturbation theory in QED
How do we access fields of this magnitude in the lab
Important parameter is χ (ratio of electric field in electron rest frame to the critical field of QED)
Beyond perturbative QED
QED in intense fields
χ = 1 means the electron sees in its rest frame a field strong enough for non-perturbative effects to dominate
Low order terms are suppressed only high order terms (ie involving large numbers of background photons) contribute
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
What about arbitrary field structures
Beyond perturbative QED
QED in intense fields
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
What do we lose by doing this
Harmonics sub-harmonics interference resonanceshellip
When is it acceptable to do so
How much bigger than 1 must a0 be
Coupling sfQED and classical processes
Locally constant field approximation
Other constraints on PIC simulations
Size of timestep must be set to avoid multiple scatterings (constraint set by rate of photon emission is strongest)
C P Ridgers et al J Comp Phys 260 273 (2014)
The rates (not cross-sections) for photon and pair production are calculated in an equivalent system of fields with the same instantaneous value of χ
eg a static magnetic field in the ultrarelativistic limit T Erber Rev Mod Phys 38 626 (1966)
Coupling sfQED and classical processes
PIC + Monte Carlo
We assumed a classical background field
Contains sufficient energy that the field is not affected by a (single) QED process
Energy is absorbed by plasmas ndash what happens to the background field
Coupling sfQED and classical processes
QED in intense fields
Creation of electron-positron pair transfers energy from background field (at interaction point)
χ 1 photon energy split evenly between electron and positron
For χ 1 most goes to one of the electron and positron
Coupling sfQED and classical processes
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
For χ 1 quantum depletion m vs classical a0
2m
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Laser absorption is increased (classically) because QED processes introduce new currents
Beyond the background field approximation
Depletion
In QED need to calculate transition rates between initial and final states that contain different numbers of photons
Does the LCFA let us take a simpler approach to calculating the effect of a QED avalanche on the background field
Beyond the background field approximation
Depletion
When does the quantum depletion have a serious effect on the background
Seipt et al PRL 118 154803 2017 for electron-beam laser collision need 10nC and a0 of 1000
Effects on angular distribution at lower intensity
Beyond the background field approximation
Depletion
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Positron production
Test bed
Electron-positron pair creation by the collision of high-energy particles with an intense laser pulse
eg wakefield accelerated electrons bremsstrahlung created gamma rayshellip
In the highly non-linear regime
Positron production
Test bed
Interaction can be modelled directly from QED (Di Piazza PRL 117 213201 2016)
Integrated full-scale QED-PIC simulations for wakefield acceleration plus photon and pair creation (Lobet et al PRAB 20 043401 2017)
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
Static electric field The field invariants are E2 ndash B2 and EB
Transform B2 rarr ndashE2 and the terms no longer alternate in sign
S has a non-perturbative imaginary part
Static magnetic field Euler-Heisenberg effective action (exact result)
Perturbative expansion is divergent but the signs alternate
Beyond perturbative QED
Perturbation theory in QED
The action for a static electric field acquires an imaginary part that is non-perturbative in the electric field strength
Stark effect = ionisation rate Here we get the pair-creation rate from the vacuum
Ecrit = 13times1018 Vm
Beyond perturbative QED
Perturbation theory in QED
How do we access fields of this magnitude in the lab
Important parameter is χ (ratio of electric field in electron rest frame to the critical field of QED)
Beyond perturbative QED
QED in intense fields
χ = 1 means the electron sees in its rest frame a field strong enough for non-perturbative effects to dominate
Low order terms are suppressed only high order terms (ie involving large numbers of background photons) contribute
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
What about arbitrary field structures
Beyond perturbative QED
QED in intense fields
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
What do we lose by doing this
Harmonics sub-harmonics interference resonanceshellip
When is it acceptable to do so
How much bigger than 1 must a0 be
Coupling sfQED and classical processes
Locally constant field approximation
Other constraints on PIC simulations
Size of timestep must be set to avoid multiple scatterings (constraint set by rate of photon emission is strongest)
C P Ridgers et al J Comp Phys 260 273 (2014)
The rates (not cross-sections) for photon and pair production are calculated in an equivalent system of fields with the same instantaneous value of χ
eg a static magnetic field in the ultrarelativistic limit T Erber Rev Mod Phys 38 626 (1966)
Coupling sfQED and classical processes
PIC + Monte Carlo
We assumed a classical background field
Contains sufficient energy that the field is not affected by a (single) QED process
Energy is absorbed by plasmas ndash what happens to the background field
Coupling sfQED and classical processes
QED in intense fields
Creation of electron-positron pair transfers energy from background field (at interaction point)
χ 1 photon energy split evenly between electron and positron
For χ 1 most goes to one of the electron and positron
Coupling sfQED and classical processes
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
For χ 1 quantum depletion m vs classical a0
2m
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Laser absorption is increased (classically) because QED processes introduce new currents
Beyond the background field approximation
Depletion
In QED need to calculate transition rates between initial and final states that contain different numbers of photons
Does the LCFA let us take a simpler approach to calculating the effect of a QED avalanche on the background field
Beyond the background field approximation
Depletion
When does the quantum depletion have a serious effect on the background
Seipt et al PRL 118 154803 2017 for electron-beam laser collision need 10nC and a0 of 1000
Effects on angular distribution at lower intensity
Beyond the background field approximation
Depletion
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Positron production
Test bed
Electron-positron pair creation by the collision of high-energy particles with an intense laser pulse
eg wakefield accelerated electrons bremsstrahlung created gamma rayshellip
In the highly non-linear regime
Positron production
Test bed
Interaction can be modelled directly from QED (Di Piazza PRL 117 213201 2016)
Integrated full-scale QED-PIC simulations for wakefield acceleration plus photon and pair creation (Lobet et al PRAB 20 043401 2017)
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
The action for a static electric field acquires an imaginary part that is non-perturbative in the electric field strength
Stark effect = ionisation rate Here we get the pair-creation rate from the vacuum
Ecrit = 13times1018 Vm
Beyond perturbative QED
Perturbation theory in QED
How do we access fields of this magnitude in the lab
Important parameter is χ (ratio of electric field in electron rest frame to the critical field of QED)
Beyond perturbative QED
QED in intense fields
χ = 1 means the electron sees in its rest frame a field strong enough for non-perturbative effects to dominate
Low order terms are suppressed only high order terms (ie involving large numbers of background photons) contribute
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
What about arbitrary field structures
Beyond perturbative QED
QED in intense fields
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
What do we lose by doing this
Harmonics sub-harmonics interference resonanceshellip
When is it acceptable to do so
How much bigger than 1 must a0 be
Coupling sfQED and classical processes
Locally constant field approximation
Other constraints on PIC simulations
Size of timestep must be set to avoid multiple scatterings (constraint set by rate of photon emission is strongest)
C P Ridgers et al J Comp Phys 260 273 (2014)
The rates (not cross-sections) for photon and pair production are calculated in an equivalent system of fields with the same instantaneous value of χ
eg a static magnetic field in the ultrarelativistic limit T Erber Rev Mod Phys 38 626 (1966)
Coupling sfQED and classical processes
PIC + Monte Carlo
We assumed a classical background field
Contains sufficient energy that the field is not affected by a (single) QED process
Energy is absorbed by plasmas ndash what happens to the background field
Coupling sfQED and classical processes
QED in intense fields
Creation of electron-positron pair transfers energy from background field (at interaction point)
χ 1 photon energy split evenly between electron and positron
For χ 1 most goes to one of the electron and positron
Coupling sfQED and classical processes
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
For χ 1 quantum depletion m vs classical a0
2m
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Laser absorption is increased (classically) because QED processes introduce new currents
Beyond the background field approximation
Depletion
In QED need to calculate transition rates between initial and final states that contain different numbers of photons
Does the LCFA let us take a simpler approach to calculating the effect of a QED avalanche on the background field
Beyond the background field approximation
Depletion
When does the quantum depletion have a serious effect on the background
Seipt et al PRL 118 154803 2017 for electron-beam laser collision need 10nC and a0 of 1000
Effects on angular distribution at lower intensity
Beyond the background field approximation
Depletion
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Positron production
Test bed
Electron-positron pair creation by the collision of high-energy particles with an intense laser pulse
eg wakefield accelerated electrons bremsstrahlung created gamma rayshellip
In the highly non-linear regime
Positron production
Test bed
Interaction can be modelled directly from QED (Di Piazza PRL 117 213201 2016)
Integrated full-scale QED-PIC simulations for wakefield acceleration plus photon and pair creation (Lobet et al PRAB 20 043401 2017)
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
How do we access fields of this magnitude in the lab
Important parameter is χ (ratio of electric field in electron rest frame to the critical field of QED)
Beyond perturbative QED
QED in intense fields
χ = 1 means the electron sees in its rest frame a field strong enough for non-perturbative effects to dominate
Low order terms are suppressed only high order terms (ie involving large numbers of background photons) contribute
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
What about arbitrary field structures
Beyond perturbative QED
QED in intense fields
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
What do we lose by doing this
Harmonics sub-harmonics interference resonanceshellip
When is it acceptable to do so
How much bigger than 1 must a0 be
Coupling sfQED and classical processes
Locally constant field approximation
Other constraints on PIC simulations
Size of timestep must be set to avoid multiple scatterings (constraint set by rate of photon emission is strongest)
C P Ridgers et al J Comp Phys 260 273 (2014)
The rates (not cross-sections) for photon and pair production are calculated in an equivalent system of fields with the same instantaneous value of χ
eg a static magnetic field in the ultrarelativistic limit T Erber Rev Mod Phys 38 626 (1966)
Coupling sfQED and classical processes
PIC + Monte Carlo
We assumed a classical background field
Contains sufficient energy that the field is not affected by a (single) QED process
Energy is absorbed by plasmas ndash what happens to the background field
Coupling sfQED and classical processes
QED in intense fields
Creation of electron-positron pair transfers energy from background field (at interaction point)
χ 1 photon energy split evenly between electron and positron
For χ 1 most goes to one of the electron and positron
Coupling sfQED and classical processes
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
For χ 1 quantum depletion m vs classical a0
2m
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Laser absorption is increased (classically) because QED processes introduce new currents
Beyond the background field approximation
Depletion
In QED need to calculate transition rates between initial and final states that contain different numbers of photons
Does the LCFA let us take a simpler approach to calculating the effect of a QED avalanche on the background field
Beyond the background field approximation
Depletion
When does the quantum depletion have a serious effect on the background
Seipt et al PRL 118 154803 2017 for electron-beam laser collision need 10nC and a0 of 1000
Effects on angular distribution at lower intensity
Beyond the background field approximation
Depletion
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Positron production
Test bed
Electron-positron pair creation by the collision of high-energy particles with an intense laser pulse
eg wakefield accelerated electrons bremsstrahlung created gamma rayshellip
In the highly non-linear regime
Positron production
Test bed
Interaction can be modelled directly from QED (Di Piazza PRL 117 213201 2016)
Integrated full-scale QED-PIC simulations for wakefield acceleration plus photon and pair creation (Lobet et al PRAB 20 043401 2017)
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
χ = 1 means the electron sees in its rest frame a field strong enough for non-perturbative effects to dominate
Low order terms are suppressed only high order terms (ie involving large numbers of background photons) contribute
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
What about arbitrary field structures
Beyond perturbative QED
QED in intense fields
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
What do we lose by doing this
Harmonics sub-harmonics interference resonanceshellip
When is it acceptable to do so
How much bigger than 1 must a0 be
Coupling sfQED and classical processes
Locally constant field approximation
Other constraints on PIC simulations
Size of timestep must be set to avoid multiple scatterings (constraint set by rate of photon emission is strongest)
C P Ridgers et al J Comp Phys 260 273 (2014)
The rates (not cross-sections) for photon and pair production are calculated in an equivalent system of fields with the same instantaneous value of χ
eg a static magnetic field in the ultrarelativistic limit T Erber Rev Mod Phys 38 626 (1966)
Coupling sfQED and classical processes
PIC + Monte Carlo
We assumed a classical background field
Contains sufficient energy that the field is not affected by a (single) QED process
Energy is absorbed by plasmas ndash what happens to the background field
Coupling sfQED and classical processes
QED in intense fields
Creation of electron-positron pair transfers energy from background field (at interaction point)
χ 1 photon energy split evenly between electron and positron
For χ 1 most goes to one of the electron and positron
Coupling sfQED and classical processes
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
For χ 1 quantum depletion m vs classical a0
2m
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Laser absorption is increased (classically) because QED processes introduce new currents
Beyond the background field approximation
Depletion
In QED need to calculate transition rates between initial and final states that contain different numbers of photons
Does the LCFA let us take a simpler approach to calculating the effect of a QED avalanche on the background field
Beyond the background field approximation
Depletion
When does the quantum depletion have a serious effect on the background
Seipt et al PRL 118 154803 2017 for electron-beam laser collision need 10nC and a0 of 1000
Effects on angular distribution at lower intensity
Beyond the background field approximation
Depletion
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Positron production
Test bed
Electron-positron pair creation by the collision of high-energy particles with an intense laser pulse
eg wakefield accelerated electrons bremsstrahlung created gamma rayshellip
In the highly non-linear regime
Positron production
Test bed
Interaction can be modelled directly from QED (Di Piazza PRL 117 213201 2016)
Integrated full-scale QED-PIC simulations for wakefield acceleration plus photon and pair creation (Lobet et al PRAB 20 043401 2017)
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
Treat the intense background as a classical field calculate transition rates to all orders
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
What about arbitrary field structures
Beyond perturbative QED
QED in intense fields
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
What do we lose by doing this
Harmonics sub-harmonics interference resonanceshellip
When is it acceptable to do so
How much bigger than 1 must a0 be
Coupling sfQED and classical processes
Locally constant field approximation
Other constraints on PIC simulations
Size of timestep must be set to avoid multiple scatterings (constraint set by rate of photon emission is strongest)
C P Ridgers et al J Comp Phys 260 273 (2014)
The rates (not cross-sections) for photon and pair production are calculated in an equivalent system of fields with the same instantaneous value of χ
eg a static magnetic field in the ultrarelativistic limit T Erber Rev Mod Phys 38 626 (1966)
Coupling sfQED and classical processes
PIC + Monte Carlo
We assumed a classical background field
Contains sufficient energy that the field is not affected by a (single) QED process
Energy is absorbed by plasmas ndash what happens to the background field
Coupling sfQED and classical processes
QED in intense fields
Creation of electron-positron pair transfers energy from background field (at interaction point)
χ 1 photon energy split evenly between electron and positron
For χ 1 most goes to one of the electron and positron
Coupling sfQED and classical processes
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
For χ 1 quantum depletion m vs classical a0
2m
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Laser absorption is increased (classically) because QED processes introduce new currents
Beyond the background field approximation
Depletion
In QED need to calculate transition rates between initial and final states that contain different numbers of photons
Does the LCFA let us take a simpler approach to calculating the effect of a QED avalanche on the background field
Beyond the background field approximation
Depletion
When does the quantum depletion have a serious effect on the background
Seipt et al PRL 118 154803 2017 for electron-beam laser collision need 10nC and a0 of 1000
Effects on angular distribution at lower intensity
Beyond the background field approximation
Depletion
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Positron production
Test bed
Electron-positron pair creation by the collision of high-energy particles with an intense laser pulse
eg wakefield accelerated electrons bremsstrahlung created gamma rayshellip
In the highly non-linear regime
Positron production
Test bed
Interaction can be modelled directly from QED (Di Piazza PRL 117 213201 2016)
Integrated full-scale QED-PIC simulations for wakefield acceleration plus photon and pair creation (Lobet et al PRAB 20 043401 2017)
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
Beyond perturbative QED
QED in intense fields
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
What about arbitrary field structures
Beyond perturbative QED
QED in intense fields
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
What do we lose by doing this
Harmonics sub-harmonics interference resonanceshellip
When is it acceptable to do so
How much bigger than 1 must a0 be
Coupling sfQED and classical processes
Locally constant field approximation
Other constraints on PIC simulations
Size of timestep must be set to avoid multiple scatterings (constraint set by rate of photon emission is strongest)
C P Ridgers et al J Comp Phys 260 273 (2014)
The rates (not cross-sections) for photon and pair production are calculated in an equivalent system of fields with the same instantaneous value of χ
eg a static magnetic field in the ultrarelativistic limit T Erber Rev Mod Phys 38 626 (1966)
Coupling sfQED and classical processes
PIC + Monte Carlo
We assumed a classical background field
Contains sufficient energy that the field is not affected by a (single) QED process
Energy is absorbed by plasmas ndash what happens to the background field
Coupling sfQED and classical processes
QED in intense fields
Creation of electron-positron pair transfers energy from background field (at interaction point)
χ 1 photon energy split evenly between electron and positron
For χ 1 most goes to one of the electron and positron
Coupling sfQED and classical processes
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
For χ 1 quantum depletion m vs classical a0
2m
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Laser absorption is increased (classically) because QED processes introduce new currents
Beyond the background field approximation
Depletion
In QED need to calculate transition rates between initial and final states that contain different numbers of photons
Does the LCFA let us take a simpler approach to calculating the effect of a QED avalanche on the background field
Beyond the background field approximation
Depletion
When does the quantum depletion have a serious effect on the background
Seipt et al PRL 118 154803 2017 for electron-beam laser collision need 10nC and a0 of 1000
Effects on angular distribution at lower intensity
Beyond the background field approximation
Depletion
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Positron production
Test bed
Electron-positron pair creation by the collision of high-energy particles with an intense laser pulse
eg wakefield accelerated electrons bremsstrahlung created gamma rayshellip
In the highly non-linear regime
Positron production
Test bed
Interaction can be modelled directly from QED (Di Piazza PRL 117 213201 2016)
Integrated full-scale QED-PIC simulations for wakefield acceleration plus photon and pair creation (Lobet et al PRAB 20 043401 2017)
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
Treat the intense background as a classical field calculate transition rates to all orders
Rates no longer diverge but now we need entire space-time structure of the background field
What about arbitrary field structures
Beyond perturbative QED
QED in intense fields
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
What do we lose by doing this
Harmonics sub-harmonics interference resonanceshellip
When is it acceptable to do so
How much bigger than 1 must a0 be
Coupling sfQED and classical processes
Locally constant field approximation
Other constraints on PIC simulations
Size of timestep must be set to avoid multiple scatterings (constraint set by rate of photon emission is strongest)
C P Ridgers et al J Comp Phys 260 273 (2014)
The rates (not cross-sections) for photon and pair production are calculated in an equivalent system of fields with the same instantaneous value of χ
eg a static magnetic field in the ultrarelativistic limit T Erber Rev Mod Phys 38 626 (1966)
Coupling sfQED and classical processes
PIC + Monte Carlo
We assumed a classical background field
Contains sufficient energy that the field is not affected by a (single) QED process
Energy is absorbed by plasmas ndash what happens to the background field
Coupling sfQED and classical processes
QED in intense fields
Creation of electron-positron pair transfers energy from background field (at interaction point)
χ 1 photon energy split evenly between electron and positron
For χ 1 most goes to one of the electron and positron
Coupling sfQED and classical processes
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
For χ 1 quantum depletion m vs classical a0
2m
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Laser absorption is increased (classically) because QED processes introduce new currents
Beyond the background field approximation
Depletion
In QED need to calculate transition rates between initial and final states that contain different numbers of photons
Does the LCFA let us take a simpler approach to calculating the effect of a QED avalanche on the background field
Beyond the background field approximation
Depletion
When does the quantum depletion have a serious effect on the background
Seipt et al PRL 118 154803 2017 for electron-beam laser collision need 10nC and a0 of 1000
Effects on angular distribution at lower intensity
Beyond the background field approximation
Depletion
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Positron production
Test bed
Electron-positron pair creation by the collision of high-energy particles with an intense laser pulse
eg wakefield accelerated electrons bremsstrahlung created gamma rayshellip
In the highly non-linear regime
Positron production
Test bed
Interaction can be modelled directly from QED (Di Piazza PRL 117 213201 2016)
Integrated full-scale QED-PIC simulations for wakefield acceleration plus photon and pair creation (Lobet et al PRAB 20 043401 2017)
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
What do we lose by doing this
Harmonics sub-harmonics interference resonanceshellip
When is it acceptable to do so
How much bigger than 1 must a0 be
Coupling sfQED and classical processes
Locally constant field approximation
Other constraints on PIC simulations
Size of timestep must be set to avoid multiple scatterings (constraint set by rate of photon emission is strongest)
C P Ridgers et al J Comp Phys 260 273 (2014)
The rates (not cross-sections) for photon and pair production are calculated in an equivalent system of fields with the same instantaneous value of χ
eg a static magnetic field in the ultrarelativistic limit T Erber Rev Mod Phys 38 626 (1966)
Coupling sfQED and classical processes
PIC + Monte Carlo
We assumed a classical background field
Contains sufficient energy that the field is not affected by a (single) QED process
Energy is absorbed by plasmas ndash what happens to the background field
Coupling sfQED and classical processes
QED in intense fields
Creation of electron-positron pair transfers energy from background field (at interaction point)
χ 1 photon energy split evenly between electron and positron
For χ 1 most goes to one of the electron and positron
Coupling sfQED and classical processes
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
For χ 1 quantum depletion m vs classical a0
2m
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Laser absorption is increased (classically) because QED processes introduce new currents
Beyond the background field approximation
Depletion
In QED need to calculate transition rates between initial and final states that contain different numbers of photons
Does the LCFA let us take a simpler approach to calculating the effect of a QED avalanche on the background field
Beyond the background field approximation
Depletion
When does the quantum depletion have a serious effect on the background
Seipt et al PRL 118 154803 2017 for electron-beam laser collision need 10nC and a0 of 1000
Effects on angular distribution at lower intensity
Beyond the background field approximation
Depletion
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Positron production
Test bed
Electron-positron pair creation by the collision of high-energy particles with an intense laser pulse
eg wakefield accelerated electrons bremsstrahlung created gamma rayshellip
In the highly non-linear regime
Positron production
Test bed
Interaction can be modelled directly from QED (Di Piazza PRL 117 213201 2016)
Integrated full-scale QED-PIC simulations for wakefield acceleration plus photon and pair creation (Lobet et al PRAB 20 043401 2017)
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
What do we lose by doing this
Harmonics sub-harmonics interference resonanceshellip
When is it acceptable to do so
How much bigger than 1 must a0 be
Coupling sfQED and classical processes
Locally constant field approximation
Other constraints on PIC simulations
Size of timestep must be set to avoid multiple scatterings (constraint set by rate of photon emission is strongest)
C P Ridgers et al J Comp Phys 260 273 (2014)
The rates (not cross-sections) for photon and pair production are calculated in an equivalent system of fields with the same instantaneous value of χ
eg a static magnetic field in the ultrarelativistic limit T Erber Rev Mod Phys 38 626 (1966)
Coupling sfQED and classical processes
PIC + Monte Carlo
We assumed a classical background field
Contains sufficient energy that the field is not affected by a (single) QED process
Energy is absorbed by plasmas ndash what happens to the background field
Coupling sfQED and classical processes
QED in intense fields
Creation of electron-positron pair transfers energy from background field (at interaction point)
χ 1 photon energy split evenly between electron and positron
For χ 1 most goes to one of the electron and positron
Coupling sfQED and classical processes
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
For χ 1 quantum depletion m vs classical a0
2m
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Laser absorption is increased (classically) because QED processes introduce new currents
Beyond the background field approximation
Depletion
In QED need to calculate transition rates between initial and final states that contain different numbers of photons
Does the LCFA let us take a simpler approach to calculating the effect of a QED avalanche on the background field
Beyond the background field approximation
Depletion
When does the quantum depletion have a serious effect on the background
Seipt et al PRL 118 154803 2017 for electron-beam laser collision need 10nC and a0 of 1000
Effects on angular distribution at lower intensity
Beyond the background field approximation
Depletion
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Positron production
Test bed
Electron-positron pair creation by the collision of high-energy particles with an intense laser pulse
eg wakefield accelerated electrons bremsstrahlung created gamma rayshellip
In the highly non-linear regime
Positron production
Test bed
Interaction can be modelled directly from QED (Di Piazza PRL 117 213201 2016)
Integrated full-scale QED-PIC simulations for wakefield acceleration plus photon and pair creation (Lobet et al PRAB 20 043401 2017)
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
If the formation length is short enough we can assume the fields are quasi-static over the emission process
The formation length is smaller than the laser wavelength by a factor of the strength parameter a0
Coupling sfQED and classical processes
Locally constant field approximation
What do we lose by doing this
Harmonics sub-harmonics interference resonanceshellip
When is it acceptable to do so
How much bigger than 1 must a0 be
Coupling sfQED and classical processes
Locally constant field approximation
Other constraints on PIC simulations
Size of timestep must be set to avoid multiple scatterings (constraint set by rate of photon emission is strongest)
C P Ridgers et al J Comp Phys 260 273 (2014)
The rates (not cross-sections) for photon and pair production are calculated in an equivalent system of fields with the same instantaneous value of χ
eg a static magnetic field in the ultrarelativistic limit T Erber Rev Mod Phys 38 626 (1966)
Coupling sfQED and classical processes
PIC + Monte Carlo
We assumed a classical background field
Contains sufficient energy that the field is not affected by a (single) QED process
Energy is absorbed by plasmas ndash what happens to the background field
Coupling sfQED and classical processes
QED in intense fields
Creation of electron-positron pair transfers energy from background field (at interaction point)
χ 1 photon energy split evenly between electron and positron
For χ 1 most goes to one of the electron and positron
Coupling sfQED and classical processes
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
For χ 1 quantum depletion m vs classical a0
2m
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Laser absorption is increased (classically) because QED processes introduce new currents
Beyond the background field approximation
Depletion
In QED need to calculate transition rates between initial and final states that contain different numbers of photons
Does the LCFA let us take a simpler approach to calculating the effect of a QED avalanche on the background field
Beyond the background field approximation
Depletion
When does the quantum depletion have a serious effect on the background
Seipt et al PRL 118 154803 2017 for electron-beam laser collision need 10nC and a0 of 1000
Effects on angular distribution at lower intensity
Beyond the background field approximation
Depletion
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Positron production
Test bed
Electron-positron pair creation by the collision of high-energy particles with an intense laser pulse
eg wakefield accelerated electrons bremsstrahlung created gamma rayshellip
In the highly non-linear regime
Positron production
Test bed
Interaction can be modelled directly from QED (Di Piazza PRL 117 213201 2016)
Integrated full-scale QED-PIC simulations for wakefield acceleration plus photon and pair creation (Lobet et al PRAB 20 043401 2017)
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
What do we lose by doing this
Harmonics sub-harmonics interference resonanceshellip
When is it acceptable to do so
How much bigger than 1 must a0 be
Coupling sfQED and classical processes
Locally constant field approximation
Other constraints on PIC simulations
Size of timestep must be set to avoid multiple scatterings (constraint set by rate of photon emission is strongest)
C P Ridgers et al J Comp Phys 260 273 (2014)
The rates (not cross-sections) for photon and pair production are calculated in an equivalent system of fields with the same instantaneous value of χ
eg a static magnetic field in the ultrarelativistic limit T Erber Rev Mod Phys 38 626 (1966)
Coupling sfQED and classical processes
PIC + Monte Carlo
We assumed a classical background field
Contains sufficient energy that the field is not affected by a (single) QED process
Energy is absorbed by plasmas ndash what happens to the background field
Coupling sfQED and classical processes
QED in intense fields
Creation of electron-positron pair transfers energy from background field (at interaction point)
χ 1 photon energy split evenly between electron and positron
For χ 1 most goes to one of the electron and positron
Coupling sfQED and classical processes
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
For χ 1 quantum depletion m vs classical a0
2m
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Laser absorption is increased (classically) because QED processes introduce new currents
Beyond the background field approximation
Depletion
In QED need to calculate transition rates between initial and final states that contain different numbers of photons
Does the LCFA let us take a simpler approach to calculating the effect of a QED avalanche on the background field
Beyond the background field approximation
Depletion
When does the quantum depletion have a serious effect on the background
Seipt et al PRL 118 154803 2017 for electron-beam laser collision need 10nC and a0 of 1000
Effects on angular distribution at lower intensity
Beyond the background field approximation
Depletion
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Positron production
Test bed
Electron-positron pair creation by the collision of high-energy particles with an intense laser pulse
eg wakefield accelerated electrons bremsstrahlung created gamma rayshellip
In the highly non-linear regime
Positron production
Test bed
Interaction can be modelled directly from QED (Di Piazza PRL 117 213201 2016)
Integrated full-scale QED-PIC simulations for wakefield acceleration plus photon and pair creation (Lobet et al PRAB 20 043401 2017)
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
Other constraints on PIC simulations
Size of timestep must be set to avoid multiple scatterings (constraint set by rate of photon emission is strongest)
C P Ridgers et al J Comp Phys 260 273 (2014)
The rates (not cross-sections) for photon and pair production are calculated in an equivalent system of fields with the same instantaneous value of χ
eg a static magnetic field in the ultrarelativistic limit T Erber Rev Mod Phys 38 626 (1966)
Coupling sfQED and classical processes
PIC + Monte Carlo
We assumed a classical background field
Contains sufficient energy that the field is not affected by a (single) QED process
Energy is absorbed by plasmas ndash what happens to the background field
Coupling sfQED and classical processes
QED in intense fields
Creation of electron-positron pair transfers energy from background field (at interaction point)
χ 1 photon energy split evenly between electron and positron
For χ 1 most goes to one of the electron and positron
Coupling sfQED and classical processes
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
For χ 1 quantum depletion m vs classical a0
2m
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Laser absorption is increased (classically) because QED processes introduce new currents
Beyond the background field approximation
Depletion
In QED need to calculate transition rates between initial and final states that contain different numbers of photons
Does the LCFA let us take a simpler approach to calculating the effect of a QED avalanche on the background field
Beyond the background field approximation
Depletion
When does the quantum depletion have a serious effect on the background
Seipt et al PRL 118 154803 2017 for electron-beam laser collision need 10nC and a0 of 1000
Effects on angular distribution at lower intensity
Beyond the background field approximation
Depletion
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Positron production
Test bed
Electron-positron pair creation by the collision of high-energy particles with an intense laser pulse
eg wakefield accelerated electrons bremsstrahlung created gamma rayshellip
In the highly non-linear regime
Positron production
Test bed
Interaction can be modelled directly from QED (Di Piazza PRL 117 213201 2016)
Integrated full-scale QED-PIC simulations for wakefield acceleration plus photon and pair creation (Lobet et al PRAB 20 043401 2017)
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
We assumed a classical background field
Contains sufficient energy that the field is not affected by a (single) QED process
Energy is absorbed by plasmas ndash what happens to the background field
Coupling sfQED and classical processes
QED in intense fields
Creation of electron-positron pair transfers energy from background field (at interaction point)
χ 1 photon energy split evenly between electron and positron
For χ 1 most goes to one of the electron and positron
Coupling sfQED and classical processes
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
For χ 1 quantum depletion m vs classical a0
2m
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Laser absorption is increased (classically) because QED processes introduce new currents
Beyond the background field approximation
Depletion
In QED need to calculate transition rates between initial and final states that contain different numbers of photons
Does the LCFA let us take a simpler approach to calculating the effect of a QED avalanche on the background field
Beyond the background field approximation
Depletion
When does the quantum depletion have a serious effect on the background
Seipt et al PRL 118 154803 2017 for electron-beam laser collision need 10nC and a0 of 1000
Effects on angular distribution at lower intensity
Beyond the background field approximation
Depletion
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Positron production
Test bed
Electron-positron pair creation by the collision of high-energy particles with an intense laser pulse
eg wakefield accelerated electrons bremsstrahlung created gamma rayshellip
In the highly non-linear regime
Positron production
Test bed
Interaction can be modelled directly from QED (Di Piazza PRL 117 213201 2016)
Integrated full-scale QED-PIC simulations for wakefield acceleration plus photon and pair creation (Lobet et al PRAB 20 043401 2017)
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
Creation of electron-positron pair transfers energy from background field (at interaction point)
χ 1 photon energy split evenly between electron and positron
For χ 1 most goes to one of the electron and positron
Coupling sfQED and classical processes
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
For χ 1 quantum depletion m vs classical a0
2m
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Laser absorption is increased (classically) because QED processes introduce new currents
Beyond the background field approximation
Depletion
In QED need to calculate transition rates between initial and final states that contain different numbers of photons
Does the LCFA let us take a simpler approach to calculating the effect of a QED avalanche on the background field
Beyond the background field approximation
Depletion
When does the quantum depletion have a serious effect on the background
Seipt et al PRL 118 154803 2017 for electron-beam laser collision need 10nC and a0 of 1000
Effects on angular distribution at lower intensity
Beyond the background field approximation
Depletion
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Positron production
Test bed
Electron-positron pair creation by the collision of high-energy particles with an intense laser pulse
eg wakefield accelerated electrons bremsstrahlung created gamma rayshellip
In the highly non-linear regime
Positron production
Test bed
Interaction can be modelled directly from QED (Di Piazza PRL 117 213201 2016)
Integrated full-scale QED-PIC simulations for wakefield acceleration plus photon and pair creation (Lobet et al PRAB 20 043401 2017)
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
For χ 1 quantum depletion m vs classical a0
2m
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Laser absorption is increased (classically) because QED processes introduce new currents
Beyond the background field approximation
Depletion
In QED need to calculate transition rates between initial and final states that contain different numbers of photons
Does the LCFA let us take a simpler approach to calculating the effect of a QED avalanche on the background field
Beyond the background field approximation
Depletion
When does the quantum depletion have a serious effect on the background
Seipt et al PRL 118 154803 2017 for electron-beam laser collision need 10nC and a0 of 1000
Effects on angular distribution at lower intensity
Beyond the background field approximation
Depletion
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Positron production
Test bed
Electron-positron pair creation by the collision of high-energy particles with an intense laser pulse
eg wakefield accelerated electrons bremsstrahlung created gamma rayshellip
In the highly non-linear regime
Positron production
Test bed
Interaction can be modelled directly from QED (Di Piazza PRL 117 213201 2016)
Integrated full-scale QED-PIC simulations for wakefield acceleration plus photon and pair creation (Lobet et al PRAB 20 043401 2017)
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
For χ 1 quantum depletion m vs classical a0
2m
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Laser absorption is increased (classically) because QED processes introduce new currents
Beyond the background field approximation
Depletion
In QED need to calculate transition rates between initial and final states that contain different numbers of photons
Does the LCFA let us take a simpler approach to calculating the effect of a QED avalanche on the background field
Beyond the background field approximation
Depletion
When does the quantum depletion have a serious effect on the background
Seipt et al PRL 118 154803 2017 for electron-beam laser collision need 10nC and a0 of 1000
Effects on angular distribution at lower intensity
Beyond the background field approximation
Depletion
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Positron production
Test bed
Electron-positron pair creation by the collision of high-energy particles with an intense laser pulse
eg wakefield accelerated electrons bremsstrahlung created gamma rayshellip
In the highly non-linear regime
Positron production
Test bed
Interaction can be modelled directly from QED (Di Piazza PRL 117 213201 2016)
Integrated full-scale QED-PIC simulations for wakefield acceleration plus photon and pair creation (Lobet et al PRAB 20 043401 2017)
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
Example photon collides with a single-wavelength linearly-polarized plane EM wave
For χ 1 quantum depletion 2m2ω vs classical a0
2m2ω
For χ 1 quantum depletion m vs classical a0
2m
Beyond the background field approximation
Depletion
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Laser absorption is increased (classically) because QED processes introduce new currents
Beyond the background field approximation
Depletion
In QED need to calculate transition rates between initial and final states that contain different numbers of photons
Does the LCFA let us take a simpler approach to calculating the effect of a QED avalanche on the background field
Beyond the background field approximation
Depletion
When does the quantum depletion have a serious effect on the background
Seipt et al PRL 118 154803 2017 for electron-beam laser collision need 10nC and a0 of 1000
Effects on angular distribution at lower intensity
Beyond the background field approximation
Depletion
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Positron production
Test bed
Electron-positron pair creation by the collision of high-energy particles with an intense laser pulse
eg wakefield accelerated electrons bremsstrahlung created gamma rayshellip
In the highly non-linear regime
Positron production
Test bed
Interaction can be modelled directly from QED (Di Piazza PRL 117 213201 2016)
Integrated full-scale QED-PIC simulations for wakefield acceleration plus photon and pair creation (Lobet et al PRAB 20 043401 2017)
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
Example photon collides with a single-wavelength linearly-polarized plane EM wave
Laser absorption is increased (classically) because QED processes introduce new currents
Beyond the background field approximation
Depletion
In QED need to calculate transition rates between initial and final states that contain different numbers of photons
Does the LCFA let us take a simpler approach to calculating the effect of a QED avalanche on the background field
Beyond the background field approximation
Depletion
When does the quantum depletion have a serious effect on the background
Seipt et al PRL 118 154803 2017 for electron-beam laser collision need 10nC and a0 of 1000
Effects on angular distribution at lower intensity
Beyond the background field approximation
Depletion
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Positron production
Test bed
Electron-positron pair creation by the collision of high-energy particles with an intense laser pulse
eg wakefield accelerated electrons bremsstrahlung created gamma rayshellip
In the highly non-linear regime
Positron production
Test bed
Interaction can be modelled directly from QED (Di Piazza PRL 117 213201 2016)
Integrated full-scale QED-PIC simulations for wakefield acceleration plus photon and pair creation (Lobet et al PRAB 20 043401 2017)
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
In QED need to calculate transition rates between initial and final states that contain different numbers of photons
Does the LCFA let us take a simpler approach to calculating the effect of a QED avalanche on the background field
Beyond the background field approximation
Depletion
When does the quantum depletion have a serious effect on the background
Seipt et al PRL 118 154803 2017 for electron-beam laser collision need 10nC and a0 of 1000
Effects on angular distribution at lower intensity
Beyond the background field approximation
Depletion
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Positron production
Test bed
Electron-positron pair creation by the collision of high-energy particles with an intense laser pulse
eg wakefield accelerated electrons bremsstrahlung created gamma rayshellip
In the highly non-linear regime
Positron production
Test bed
Interaction can be modelled directly from QED (Di Piazza PRL 117 213201 2016)
Integrated full-scale QED-PIC simulations for wakefield acceleration plus photon and pair creation (Lobet et al PRAB 20 043401 2017)
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
When does the quantum depletion have a serious effect on the background
Seipt et al PRL 118 154803 2017 for electron-beam laser collision need 10nC and a0 of 1000
Effects on angular distribution at lower intensity
Beyond the background field approximation
Depletion
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Positron production
Test bed
Electron-positron pair creation by the collision of high-energy particles with an intense laser pulse
eg wakefield accelerated electrons bremsstrahlung created gamma rayshellip
In the highly non-linear regime
Positron production
Test bed
Interaction can be modelled directly from QED (Di Piazza PRL 117 213201 2016)
Integrated full-scale QED-PIC simulations for wakefield acceleration plus photon and pair creation (Lobet et al PRAB 20 043401 2017)
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
Introduction
What are the challenges
QED in strong electromagnetic fields
Coupling QED to classical plasma physics
Experimental observation with currently available laser systems
Positron production
Test bed
Electron-positron pair creation by the collision of high-energy particles with an intense laser pulse
eg wakefield accelerated electrons bremsstrahlung created gamma rayshellip
In the highly non-linear regime
Positron production
Test bed
Interaction can be modelled directly from QED (Di Piazza PRL 117 213201 2016)
Integrated full-scale QED-PIC simulations for wakefield acceleration plus photon and pair creation (Lobet et al PRAB 20 043401 2017)
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
Positron production
Test bed
Electron-positron pair creation by the collision of high-energy particles with an intense laser pulse
eg wakefield accelerated electrons bremsstrahlung created gamma rayshellip
In the highly non-linear regime
Positron production
Test bed
Interaction can be modelled directly from QED (Di Piazza PRL 117 213201 2016)
Integrated full-scale QED-PIC simulations for wakefield acceleration plus photon and pair creation (Lobet et al PRAB 20 043401 2017)
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
Positron production
Test bed
Interaction can be modelled directly from QED (Di Piazza PRL 117 213201 2016)
Integrated full-scale QED-PIC simulations for wakefield acceleration plus photon and pair creation (Lobet et al PRAB 20 043401 2017)
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
Positron production
Scaling laws
Can obtain analytical expressions for the photon spectrum the energy of those that pair create and the positron energy
Total number of positrons is given by the integral of the photon spectrum weighted by the pair creation probability
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
Positron production
Scaling laws
Necessary collision parameters
To create 100 positrons from 100 pC of charge need
for a 30fs pulse
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
Positron production
Scaling laws
Synchronisation and overlap between the beams
Beam size effects theory predicts 10500 pairs from collision between 100pC electron beam (2 GeV 10 micron size) and laser pulse I21 = 5 800nm wavelength and 2 micron waist 3D PIC gives 10000
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-
Many theoretical questions remain how to account for back-reaction and multiphoton effects self-consistently in QED
How will the answers to those questions inform simulation development Is the QED-PIC model sufficient
Experimental work is of critical importance ndash and can be done with currently available laser systems
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- Slide 39
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Slide 44
- Slide 45
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Slide 54
- Slide 55
- Slide 56
- Slide 57
- Slide 58
- Slide 59
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Slide 64
- Slide 65
- Slide 66
- Slide 67
- Slide 68
- Slide 69
- Slide 70
- Slide 71
- Slide 72
- Slide 73
- Slide 74
- Slide 75
- Slide 76
- Slide 77
- Slide 78
- Slide 79
- Slide 80
- Slide 81
- Slide 82
-