signatures of strong-field qed effects in high- intensity laser-matter interactions ·...

Signatures of strong-field QED effects in high-intensity laser-matter interactions

C. P. RidgersYork Plasma Institute, Department of PhysicsUniversity of York

Authors

York Plasma Institute: D. Del Sorbo, D. R. Blackman, C. Slade-Lowther, K. Small, J. Pasley, C. D. Murphy, L.E. Bradley, C.D. Baird

University of Strathclyde: R. Capdessus, W. Luo, M. J. Duff, P. McKenna, Z.-M. Sheng

Central Laser Facility: A. P. L. Robinson

Cockroft Institute/University of Lancaster: D. Seipt

Cockroft Institute, University of Lancaser & University of Michigan: A. G. R. Thomas

Chalmers University of Technology: T. G. Blackburn, M. Marklund

Max Planck Institute for Nuclear Physics: J. G. Kirk

Imperial College London: S.P.D. Mangles

Outline

How strong is a 'strong-field'? Introduction to QED model

Laser absorption by self-generated pair plasmas

Experiments we can perform now?

Spin polarisation of the plasma

Rapid Increase in Laser Intensity

1960 1980 2000 2020

1016

1020

1024

Intensity/Wcm-2

Year

Rapid increase in laser intensity


1960 1980 2000 2020

1016

1020

1024

Intensity/Wcm-2

Year


Hercules (UMICH) → 2x1022Wcm-2


1960 1980 2000 2020

1016

1020

1024

Intensity/Wcm-2

Year



Plasma


1960 1980 2000 2020

1016

1020

1024

Intensity/Wcm-2

Year



Relativistic Plasma

Plasma


1960 1980 2000 2020

1016

1020

1024

Intensity/Wcm-2

Year



QED Plasma

Relativistic Plasma

Plasma


1960 1980 2000 2020

1016

1020

1024

Intensity/Wcm-2

Year



APOLLON, ELI, Texas PW

QED Plasma

Relativistic Plasma

Plasma

Intensity to reach QED-plasma regime

Field does work ~mec2 over l

c eE slc=mec

2



c

E s=me c

2

elc=1.3 x1018Vm−1

eE slc=mec2

I s=2x1029Wcm−2



c

E s=me c

2

elc=1.3 x1018Vm−1

eE slc=mec2

I s=2x1029Wcm−2

Lab frame:= E s

∣E ⊥v×B∣η=ERFE s

Important parameter:



c

E s=me c

2

elc=1.3 x1018Vm−1

eE slc=mec2

I s=2x1029Wcm−2

Lab frame:= E s

∣E ⊥v×B∣

∣E⊥ +v×B∣∼E laserAssume a=e Elaserme cωlaser

γ∼a

η=ERFE s




c

E s=me c

2

elc=1.3 x1018Vm−1

eE slc=mec2

I s=2x1029Wcm−2

Lab frame:= E s

∣E ⊥v×B∣

∣E⊥ +v×B∣∼E laserAssume a=e Elaserme cωlaser

γ∼a

Putting these into formula for η η∼0.1I

5×1022Wcm−2

η=ERFE s


Why are strong-field interactions with matter interesting?

1. Applications – compact particle accelerator



Ion acceleration by light pressure?



Light pressure important at >1023Wcm-2

Ion acceleration by light pressure?


2. Fundamental physics

'Strong-field interaction': very non-linear Compton scattering.




Particle basis states 'dressed' by background fields




Only possible to determine basis states in a few special background fields → plane waves, constant crossed electric and magnetic fields

Particle basis states 'dressed' by background fields


3. New plasma regime – non-linear QED processes occur in plasma


3. New plasma regime – non-linear QED processes occur in plasma

FEEDBACKQED processes

Classical Plasma Physics

Quasi-classical model

1. Split EM field into 'low frequency' background (laser-fields) & 'high frequency' emitted (gamma-rays) components

C.P. Ridgers et al, J Comp Phys, 260, 273 (2014)



2. 'Low frequency' fields are treated classically

C.P. Ridgers et al, J Comp Phys, 260, 273 (2014)




3. Use strong-field QED – basis states dressed by fields – motion classical between emissions

C.P. Ridgers et al, J Comp Phys, 260, 273 (2014) V.N. Baier, 'High Energy Processes in Aligned Single Crystals'






4. Keep lowest order interactions between electrons, positrons, gamma-rays with classical low frequency fields






4. Keep lowest order interactions between electrons, positrons, gamma-rays with classical low frequency fields

Photon emission

Pair production

Electromagnetic Cascade

+

Results in exponential growth in number of pairs

Outline





Circular polarisationI=5x1024Wcm-2

Pulse duration ~30fs Wavelength = 1 micronSpot size 3.3 microns

Target:Al – e- density 1030m-3

Fully ionised Semi-infinite

Laser:

D. Del Sorbo, et al, arXiv:1706.04153

Ion acceleration reduced by ‘pair cushion’


Electron density

Ion densityLaser intensity



Electron density

Ion density

Positron density

Laser intensity


Radiation pressure of laser pulse accelerates ions...


Electron density

Ion density

Positron density

Laser intensity


Radiation pressure of laser pulse accelerates ions...


Electron density

Ion density

Positron density

Laser intensity

… but eventually generates an overdense pair plasma which absorbs the energy and curtails acceleration



Laser

Ions

Hole-boringfront

SolidVacuum

Laboratory frame



Laser

Ions

SolidVacuum

Laser

Ions

Hole-boringfront

SolidVacuum

Laboratory frame Hole-boring frame



Laser

Ions

SolidVacuum

Laser

Ions

Hole-boringfront

SolidVacuum


Initially laser pulse perfectly reflected in HB frame



Laser

Ions

SolidVacuum

Laser

Ions

Hole-boringfront

SolidVacuum



After some time pair cascade results in critical density pair plasma…..

Pair cushion



Laser

Ions

SolidVacuum

Laser

Ions

Hole-boringfront

SolidVacuum



γ-rayemission

Pair cushion

After some time pair cascade results in critical density pair plasma…..

…..which radiates energy and laser pulse not perfectly reflected


Ion acceleration or pair production?



Pair plasmacreation



Pair plasmacreation

Ion acceleration


Feedback



Absorption curtails ion acceleration

Feedback



Absorption curtails ion acceleration

Skin effect curtails absorption

Outline






1960 1980 2000 2020

1016

1020

1024

Intensity/Wcm-2

Year



Electron Beam – Laser Pulse Collisions

η∼0.1I

5×1022Wcm−2


η∼0.1I

5×1022Wcm−2

∣E⊥ +v×B∣∼E laser

Assume a=e Elaserme cωlaser

γ∼a


η∼0.1I

5×1022Wcm−2

∣E⊥ +v×B∣∼E laser

Assume a=e Elaserme cωlaser

γ∼a

η∼0.1γme c

2

500MeVI

1021Wcm−2

Signatures of strong-field QED effects

We can reach ~1GeV and 1021Wcm-2 so η~0.1

η∼0.1γme c

2

500MeVI

1021Wcm−2



η∼0.1γme c

2

500MeVI

1021Wcm−2

Sufficient to study photon emission and quantum effects on radiation reaction



η∼0.1γme c

2

500MeVI

1021Wcm−2

Sufficient to study photon emission and quantum effects on radiation reaction

1. Decrease in power radiated compared to classical2. Probabilistic nature of emission


∂ f∂ t

=−l f +ηγ∫γ

∞lρ f ( p ')

p '2

p2 dp '

Starting with a quantum ‘emission operator’….

C.P. Ridgers, et al, submitted to JPP (2017)


∂ f∂ t

=−l f +ηγ∫γ

∞lρ f ( p ')

p '2

p2 dp '


Electrons leave a region of phase space by emitting a photon and losing energy



∂ f∂ t

=−l f +ηγ∫γ

∞lρ f ( p ')

p '2

p2 dp '


Electrons leave a region of phase space by emitting a photon and losing energy

Electrons with higher energy enter the region of phase space as they emit



∂ f∂ t

=−l f +ηγ∫γ

∞lρ f ( p ')

p '2

p2 dp '


…. we can get equations for the evolution of the mean and variance of the energy



∂ f∂ t

=−l f +ηγ∫γ

∞lρ f ( p ')

p '2

p2 dp '



d ⟨ γ ⟩d t

=−⟨gP ⟩me c

2

dσ2

d t=

⟨ S⟩me

2c4 −⟨Δ γ gP⟩mec

2



∂ f∂ t

=−l f +ηγ∫γ

∞lρ f ( p ')

p '2

p2 dp '



d ⟨ γ ⟩d t

=−⟨gP ⟩me c

2

dσ2

d t=

⟨ S⟩me


2

Classically synchrotron losses narrow the electron spectrum


∂ f∂ t

=−l f +ηγ∫γ

∞lρ f ( p ')

p '2

p2 dp '



d ⟨ γ ⟩d t

=−⟨gP ⟩me c

2

dσ2

d t=

⟨ S⟩me


2

Classically synchrotron losses narrow the electron spectrum

Quantum synchrotron effects can broaden the spectrum


γ

Distribution

Initial


γ

Distribution

InitialFinal - classical


γ

Distribution

InitialFinal - classical

Final - quantum


<γ>

time/10fs time/10fs

QuantumQuantum

ClassicalClassical

d ⟨ γ ⟩d t

=−⟨gP ⟩me c

2


<γ> σ

time/10fs time/10fsd ⟨ γ ⟩d t

=−⟨gP ⟩me c

2

dσ2

d t=

⟨ S⟩me


2

QuantumQuantum

ClassicalClassical

Outline





Sokolov-Ternov effect

Electron radiating in a strong magnetic field - asymmetry in rate of spin flip…..



…. electron spin polarizes anti-parallel to B-field (positrons parallel)



…. electron spin polarizes anti-parallel to B-field (positrons parallel)

Observed in storage rings: 1GeV electron in a 10kG magnetic field - 92.4% probability of spin anti-alignment after 1 hour

Analogous effect in laser fields?



Electron radiating in a rotating electric field - asymmetry in rate of spin flip…..




…. electron spin polarizes anti-parallel to Exb (positrons parallel)




…. electron spin polarizes anti-parallel to Exb (positrons parallel)

Can this occur on the relevant fs timescale?


Spin polarisation in laser fields


Spin polarisation in laser fields

90% of electrons spin polarised anti-parallel to Exb


Signatures of spin polarisation

Is this important?



Is this important?

1. Modifies radiation reaction by ~20%



Is this important?


2. Modifies polarisation of photons by ~30%



Is this important?


2. Modifies polarisation of photons by ~30%

3. Applications of spin polarised plasmas and electron beams?


Conclusions

Strong field QED processes are predicted to play a major role in 10PW laser-plasma interactions

Conclusions


Signatures include: curtailing ion acceleration (reducing energy by up to 65%); spin polarisation of the plasma

Conclusions


Signatures include: curtailing ion acceleration (reducing energy by up to 65%); spin polarisation of the plasma

These processes can be measured using current PW lasers (colliding with energetic electron beam). Signatures: reduction in power radiated, stochasticity

Additional slides


Analytical model for energy reduction – balance momentum in ‘hole boring’ frame


C.P. Ridgers, et al, PRL, 108, 165006 (2012)


ϵ=mI c

2 2Π1+2√Π ϕ=mI c

2 2√Π1+2√Π

1+R2

Ion energy Efficiency




ϵ=mI c

2 2Π1+2√Π ϕ=mI c

2 2√Π1+2√Π

1+R2

Π=1+R2

I5×1023Wcm−2 ( ρ

1 gcm−3 )−1


Both depend on




ϵ=mI c

2 2Π1+2√Π ϕ=mI c

2 2√Π1+2√Π

1+R2

Π=1+R2

I5×1023Wcm−2 ( ρ

1 gcm−3 )−1


Both depend on

Reflection coefficient in hole-boring frame important


Simulation – cascade off

Theory - R=1



Simulation – cascade off

Theory - R=1

Simulation – cascade on

Theory - R<1


QED-PIC Codes

Push particles

Update E & B

CurrentE & B 'Standard' PIC code

QED-PIC Codes

Update QED rate equations

Push particles

Update E & B

E & B

Particle energies

QED-PIC codeCurrentE & B

QED-PIC Codes


Generate photon/pair

Push particles

Update E & B

E & B

Particle energies

Add particles to PIC code

QED-PIC code

Generate photon/pair?

YES

NO

CurrentE & B

QED-PIC Codes


Generate photon/pair

Push particles

Update E & B

E & B

Particle energies

Add particles to PIC code

QED-PIC code

Generate photon/pair?

YES

NO

Monte-Carlo emission algorithm

CurrentE & B



ϵ=mI c

2 2Π1+2√Π ϕ=mI c

2 2√Π1+2√Π

1+R2





ϵ=mI c

2 2Π1+2√Π ϕ=mI c

2 2√Π1+2√Π

1+R2

Π=0.2I

5×1023Wcm−2 ( ρ1 gcm−3 )

−1 1+R2


Both depend on


Π=0.2I

5×1023Wcm−2 ( ρ1 gcm−3 )

−1 1+R2



ϵ=mI c

2 2Π1+2√Π ϕ=mI c

2 2√Π1+2√Π

1+R2


Both depend on

Reflection coefficient in hole-boring frame important


Π=0.2I

5×1023Wcm−2 ( ρ1 gcm−3 )

−1 1+R2



ϵ=mI c

2 2Π1+2√Π ϕ=mI c

2 2√Π1+2√Π

1+R2


Both depend on

in weakly relativistic case Π≪1R=0


Gives 50% reduction in ion energy and 65% reduction in efficiency

Π=0.2I

5×1023Wcm−2 ( ρ1 gcm−3 )

−1 1+R2



ϵ=mI c

2 2Π1+2√Π ϕ=mI c

2 2√Π1+2√Π

1+R2


Both depend on

In strongly relativistic case Π≫1R=0Gives 30% reduction in ion energy and 50% reduction in efficiency


signatures of strong-field qed effects in high- intensity laser-matter interactions ·...

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