Measuring E and B fields in Laser-produced Plasmas with Monoenergetic Proton Radiography

9th International Fast Ignition Workshop

C. K. Li MIT Cambridge, MA 3-5 Nov. 2006

FSC

MITMIT

Collaborators

F. H. SéguinJ. A. FrenjeJ. R. Rygg

R. D. Petrasso

MIT

R. P. J. TownP. A. AmendtS. P. HatchettO. L. Landen

A. J. MackinnonP. K. PatelM. Tabak

LLNL

J. P. KnauerT. C. SangsterV. A. Smalyuk

LLE

FSC

MITMIT

Summary

A monoenergetic backlighter proton spectrum simplifies experiment design and interpretation.

High-resolution, time gated radiography images of a plastic foil driven by a 1014 W/cm2 laser implied B fields of ~ 0.5 MG and E fields of ~ 1.5108 V/m.

Simulations of these experiments with LASNEX+LSP are in overall agreement with the data both for field strengths and for spatial distributions while the laser is on; this is the first direct experimental test of the B-field generation package in LASNEX.

The experiments also demonstrated that laser phase plates substantially reduce medium-scale chaotic field structure.

E and B fields generated by the interaction with plasmas of long-pulse, low-intensity laser beams relevant to ICF are measured with novel monoenergetic proton radiography

The generation of E and B fields by laser-plasma interactions is a process of fundamental interest in

high-energy density (HED) physics

5 m CH 1 ns squarespot diameter 800 m I ~ 1014 W/cm2

Laser

Te

ne

eee

Tnen

1

BvB

t

Grid

D3He-

implosion

backlighter

Laser beamMesh and foil

Implosion

Before laser~ 0.6 ns

after laser

Meshcartoon image

real images

Proton radiographs already made of B fields generated by laser-plasma interactions

demonstrate feasibility for Fast Ignition studies

The same concept can be applied to investigate B field generated by short-pulse laser-plasma interaction

Fast ignition (Short pulse)

eLaserprotons

Laserprotons

Monoenergetic protons can be generated in nuclear fusion reactions through ICF implosions

2 m SiO2

0

5

10

0 5 10 15 20Energy (MeV)

Yie

ld /

MeV

(x

108)

DD proton

D3He proton

D + 3He + p (14.7 MeV)

D + D T + p (3.0 MeV)

RSI 2006

Several nuclear and x-ray diagnostics are used to characterize the proton backlighter

0 5 10 15 20Energy (MeV)

Yield

Proton spectrum

Proton emission image

0 500 1000 1500Time (ps)

x-ray emission imageProtons

Laser

Proton production history

E and B fields can be simultaneously measured using a single proton backlighter

mesh

“Backlighter”

Backlighter drive beams

CR-39

Interaction beam

CH foil

side-on

face-on

Face-on radiography is sensitive to the B field, while side-on radiography is sensitive to the E field

Experimental data and LASNEX+LSP simulations agree both for field strengths and for spatial distributions

SimulationBy R. Town

Data

2.3mm

0 ns 0.33 ns 0.64 ns

0 ns 0.30 ns 0.63 ns

PRL 2006

0.30 ns 0.63 ns

R (cm)

0.06

0.03

0

-0.03

-0.06

0.08 0.04 0 0.08 0.04 0 Z (cm)

0.05 0.35 0.65 0.95 MG

Laser

LASNEX simulations indicate that the toroidal B fields are concentrated on a hemispherical shell

surrounding the ablative plasma bubble

0.3 ns 0.6 ns

Experimental data and LASNEX+LSP simulation show that the largest B field occurs near the surface

of the plasma bubble

protons

Simulation

Data

The smaller diameter of the SG2 beam resulted in an intensity 2.6 times higher than SG4, causing greatly

increased image distortion.

SG4

0 ns 0.41 ns 0.71ns

2.3 mm

SG2

0 ns 0.41 ns 0.77ns

Experiments demonstrate that laser phase plates substantially reduce medium-scale chaotic field structure

2.3mm

With phase plates Without phase plates

A CH foil driven by a 1014 W/cm2 laser beam results in E field of ~ 1.5108 V/m

E Ep Te/Te

lineout

Lineout Simulation

Data 2.3

mm

MITMIT

Summary

A monoenergetic backlighter proton spectrum simplifies experiment design and interpretation.

High-resolution, time gated radiography images of a plastic foil driven by a 1014 W/cm2 laser implied B fields of ~ 0.5 MG and E fields of ~ 1.5108 V/m.

Simulations of these experiments with LASNEX+LSP are in overall agreement with the data both for field strengths and for spatial distributions while the laser is on; this is the first direct experimental test of the B-field generation package in LASNEX.

The experiments also demonstrated that laser phase plates substantially reduce medium-scale chaotic field structure.

E and B fields generated by the interaction with plasmas of long-pulse, low-intensity laser beams relevant to ICF are measured with novel monoenergetic proton radiography