Measurement of Magnetic fieldin intense laser-matter interactionvia Relativistic electron deflectometry

Osaka University

*N. Nakanii, H. Habara, K. A. Tanaka

University of California San Diego

T. Yabuuchi, H. Sawada, B.S. Paradkar, M.S. Wei, F.N. Beg

General Atomics

R.B. Stephens

University of Michigan

C. McGuffey, K. Krushelnick

* Also at University of California San Diego

Outline

• Motivation

• Laser-driven relativistic electron deflectometry

• Measurement of B field in intense laser-solid interaction– Long-pulse (ns) low-intensity (~ 1014 W/cm2)

• Proposed experiment• Integrated rad-hydro/hybrid PIC modeling

– Short-pulse (fs-ps) high-intensity (> 1018 W/cm2)• Experimental plan

• Summary

Outline

• Motivation

• Laser-driven relativistic electron deflectometry

• Measurement of B field in intense laser-solid interaction– Long-pulse (ns) low-intensity (~ 1014 W/cm2)

• Proposed experiment• Integrated rad-hydro/hybrid PIC modeling

– Short-pulse (fs-ps) high-intensity (> 1018 W/cm2)• Experimental plan

• Summary

Motivation

• Characterization of strong spontaneous magnetic (B) fields in intense laser-matter interaction is an important issue in High Energy Density (HED) sciences.

– Fast ignition (Electron energy transport)

– Generation of energetic electrons, ions, and x-rays

– and so on…

Strong spontaneous magnetic fields are generated in laser-matter interactions

• Long-pulse (ns) low-intense (-1014W/cm2) laser– ∇T x n in ablated plasma (dominantly)∇– 100 kGauss ~ MGauss

• Short-pulse (fs~ps) high-intense (>1018W/cm2) laser– ∇T x n∇

Ponderomotive force

Current of fast electrons

and etc…– Over 100 Mega-Gauss

€

∇T ×∇n

Outline

• Motivation

• Laser-driven relativistic electron deflectometry

• Measurement of B field in intense laser-solid interaction– Long-pulse (ns) low-intensity (~ 1014 W/cm2)

• Proposed experiment• Integrated rad-hydro/hybrid PIC modeling

– Short-pulse (fs-ps) high-intensity (> 1018 W/cm2)• Experimental plan

• Summary

Intense laser-driven electrons have advantages to diagnose B field with deflectometry method

Enough particle number for imaging

[Laser-solid] ~ 1011 with broad energy spread

[LWFA] > 108 with monoenergetic spectrum

Variable energies enable to detect wide-range B field

[Laser-solid] up to several ten MeV

[LWFA] up to 1 GeV

Ultrashort pulse duration can provide high temporal resolution

[Laser-solid] a few ps

[LWFA] several ten fs

Small source size can provide high spatial resolution

~ focal spot size

Relativistic electrons have advantages to measure B field in overdense plasmas

Relativistic electrons are penetrative in dense matter without significant energy loss in a short time

The electrons are susceptive to B field because they have the high velocity ~ c

€

F = q(E+ v ×B)

Laser-produced relativistic electrons are very useful for measuring the B field with deflectometry method

B field with wide range of strength or scale can be detected by using laser-produced electrons

Deflection angle

Changing the electron energy, different range of B field can be detected.

360[deg]

180

90

10

1

0.1

0.01

0.001

1e-4

Trapped electrons

Deflection angle map with respect to e- energy and integrated B field along e- path

RelativisticNon-relativistic

€

θd =e

m0c

B × dlL

∫

m0c2 +ε km0c

2

⎛

⎝ ⎜

⎞

⎠ ⎟

2

−1

Integrated B fieldalong e- path

Kinetic energy

Outline

• Motivation

• Laser-driven relativistic electron deflectometry

• Measurement of B field in intense laser-solid interaction– Long-pulse (ns) low-intensity (~ 1014 W/cm2)

• Proposed experiment• Integrated rad-hydro/hybrid PIC modeling

– Short-pulse (fs-ps) high-intensity (> 1018 W/cm2)• Experimental plan

• Summary

Experiment to measure ns-laser-produced B fields with relativistic electron deflectometry is proposed

We demonstrated the feasibility of this relativistic electron deflectmetry using hybrid PIC (LSP) and rad-hydro code (h2d)

Schematic of proposed experiment

Electrons are produced in short pulse laser interaction with solid

10 MeV electrons with narrow-bandwidth (~0.3 MeV) are selected by a pair magnet and used as backlighter

Mesh provides initial spatial information of electron beam

Integrated rad-hydro/hybrid PIC modeling

Rad-hydro code (h2d):B field & Ablated plasma

profile

Z

R

Target

Long pulse

Ablated plasma& B field

0.1 Mega-Gauss toroidal B field generated around laser spot near the critical dense region

Laser (~ Titan long pulse @LLNL)• Energy 100J• Pulse width 1ns (square)• Wavelength 0.5um• Spot size 300um• Intensity 1.4x1014 W/cm2

Target• Polystyrene plane• Thickness 50umB field map at 1.5 ns after the laser

irradiation (2D Cylindrical geometry)

Integrated rad-hydro/hybrid PIC modeling

Hybrid PIC code (LSP): Deflection of probe

e- beam by the B field

e- source(10MeV)

LSP Simulation area

Z

Target

Long pulse

Ablated plasma& B field

Mesh(30um)

2mm 0.7mm

Electron bunch path w/o B field

Deflected electron path by B fieldRad-hydro code (h2d):

B field & Ablated plasma

profile

Electron bunches were passing through CH plasma and slightly deflected by the B field

Solid dense region

Corona plasma regionTe: 300 eV, Ti: 250 eV,Ave Z: 3.5

0.1334ps

0.5337ps 1.400ps 2.200ps

Track of electron bunches in LSP simulation

Integrated rad-hydro/hybrid PIC modeling

Shift

Target

Long pulse

Ablated plasma& B field

e- source(10MeV)

Detector

Shift

Z

Mesh(30um)

10cm

Extra calculations:e- distribution on

detectorDeflection angle

Rad-hydro code (h2d):B field & Ablated plasma

profile

Hybrid PIC code (LSP): Deflection of probe

e- beam by the B field

Electron bunches were slightly focused to center by the toroidal B field

• Deflection angle at the each point was calculated from the spike shift in the distribution on detector.

(b) w/o plasma and B field(a) w/ plasma and B field

Electron distribution on detector

Deflected

Integrated rad-hydro/hybrid PIC modeling

Shift

Target

Long pulse

Ablated plasma& B field

e- source(10MeV)

Detector

Shift

Z

Mesh(30um)

Extra calculation:e- distribution on

detectorDeflection angle

10cm

Reconstruction of integrated B field profile

Rad-hydro code (h2d):B field & Ablated plasma

profile

Hybrid PIC code (LSP): Deflection of probe

e- beam by the B field

0 0.01 0.02 0.03 0.04 0.05 0.060.0E+00

2.0E+00

4.0E+00

6.0E+00

8.0E+00

1.0E+01

0.0E+00

2.0E-01

4.0E-01

6.0E-01

8.0E-01

1.0E+00

1.2E+00

1.4E+00

1.6E+00 Integrated B fiield along z di-rection (Actual one from hydro simulation)

Deflection angle and Inte-grated B along electron path (Reconstructed)

R [cm]

Inte

gra

ted

B f

ield

[M

Ga

us

s u

m]

De

fle

cti

on

an

gle

[d

eg

]

Distribution of integrated B field reconstructed from deflection angle are comparable to actual one

€

B× dl =m0cθ de

m0c2 +ε km0c

2

⎛

⎝ ⎜

⎞

⎠ ⎟

2

−1L

∫

€

θd : deflection angle

ε k : kinetic energy

Deflection angles and profile of reconstructed integrated B field and actual one.

Outline

• Motivation

• Laser-driven relativistic electron deflectometry

• Measurement of B field in intense laser-solid interaction– Long-pulse (ns) low-intensity (~ 1014 W/cm2)

• Proposed experiment• Integrated rad-hydro/hybrid PIC modeling

– Short-pulse (fs-ps) high-intensity (> 1018 W/cm2)• Experimental plan

• Summary

Experiment to measure fs ultra-intense laser produced B fields with LWFA monoenegetic electrons

• Monoenergetic relativistic electron beam is created by laser wakefield acceleration with gas-jet.

• Deflected electrons pass through the hole of 2nd OAP and are detected • Temporal evolution of the B field can be observed by changing the

delay of optical delay unit with ultra-short time resolution

Summary

• We proposed a B field deflectometry experiment using laser-produced relativistic electrons

• We demonstrated the feasibility of electron deflectmetry to measure the B field produced in ns-laser-matter interaction using hybrid PIC (LSP) and rad-hydro code (h2d)

• Integrated magnetic field along electron path can be reconstructed from the deflected electron distribution on deflection

• Experiment for measuring B field in interaction of ultra-intense laser with solid will be performed soon

Acknowledgements

This work supported by

– Japan Society for the Promotion of Sciences (JSPS)

Research Fellowship DC1

– Global COE Program

Center for Electronic Device Innovation (CEDI)

– U.S. Department of Energy

DE-FG-02-05ER54834 (ACE)

– JSPS Core-to-Core Program

International Collaboration for High Energy Density Science (ICHEDS)