Imploding cone-in-shell

capsule

2.7 mm

15-MeV proton backlighter

Imaging detector

Protons per unit area on detector

protons

Proton Radiography of Electromagnetic Fields in Laser-Produced High-Energy-Density Plasmas

HEDLP Workshop Washington DC August 08C. K. Li MIT

MITMIT

SummaryTime-gated, monoenergetic proton radiography provides unique measurements of E+B fields in laser-produced HED plasmas

• Radiography of laser-foil interactions:

Observation generations of ~106 gauss B field and 109 V/m E field Observation of decay dynamics and instabilities of MG B field Observation of field topology change due to magnetic reconnection

• Radiography of direct-drive cone-in-shell/spherical implosions:

Observation of radial, filamentary structures with complex striations and bifurcations, of B field magnitude 0.6×106 gauss

Observation of radial E field of order 109 V/m and its direction reversal

• Radiography of laser-irradiated gold hohlraums:

Observation of ~106 gauss B field and its evolution Observation of ~109 V/m E field and its evolution

LLE-UR

R. BettiJ. DelettrezV. GoncharovJ. KnauerF. MarshallD. MeyerhoferV. Smalyuk

Collaborators

MIT

F. SéguinJ. FrenjeR. PetrassoM. Manuel (G)D. Casey (G)N. Sinenian (G)

LLNL

P. AmendtO. LandenJ. RyggR. Town

GA

C. BackJ. KilkennyA. Nikroo

The proton source is a laser-driven glass capsule filled with D2 and 3He gas

0 10 20

6×108

0

(MeV)

protonsMeV

source spectrum

3% FWHM

3×1018

0

(ns)

protonss

0 0.5 1

source emission

130 psFWHM

14.7 MeV protons

D + 3He → 4He + p (14.7 MeV)

Heating of the gas during implosionleads to nuclear fusion production:Source

Emission of 14.7 MeV D3He protons is pulsed, monoenergetic, and isotropic

PRL 2006

Radiographs of laser-generated plasma bubbles on opposite sides of a foil prove that deflecting fields are B rather than E

OMEGA shot 46535

dBξ pvpm A

a)-qa(A

a

A

Petrasso et al APS 2007

Data and LASNEX simulations are similar with the laser on, but diverge afterwards

Interaction laseron for 1 ns

5mm

Outer bubble Burn-through hole

0.3 ns 0.6 0.9 1.2 1.5 1.8 2.3 3.0 ns

0

500

0 1 2 3

Time (ns)

0

0.6

La

ser

po

we

r (T

W)

0

2000

0

0.6

La

ser

po

we

r (T

W)

Meanbubbleradius(µm)

(a)

(b)

RMS bubble

asymmetry(µm)

0

250

0 1 2 3

Time (ns)

0

0.6

La

ser

po

we

r (T

W)(c)

Bdℓ (MG-µm)

2D code LASNEX produces credible simulations of the hydrodynamics and field growth as long as the laser was on, failing only when 3D instabilities appeared.

LASNEX+LSP by R. Town

PRL 2007a

0

200

0 1 2 3 4 5

Position along lineout (mm)

Magnetic reconnection has been observed and quantified

5 mm

Bdℓ(MG-µm)

0.31 ns 0.51 ns 0 .69 ns 0.97 ns 1.24 ns 1.72 ns 2.35 ns

5mm

0.04 ns 0.67 ns 1.42 ns

Bdℓ(MG-µm)

0

200

0 1 2 3 4 5

Position along lineout (mm)

> 95% field strength was reduced in the region where bubbles overlap

PRL 2007b

Face-on 15-MeV radiographs show the evolution from “corrugated” to cellular structures

0 1 2 3Time (ns)

Drive laser

~0.6 MG fields in these cellular structures with cell size ~ 120 μm

Position (µm)

P-P amp. ~ 18%

Position (µm)

P-P amp. ~ 5%

Diameter = 2.5 mmThickness = 20±1 mModulation ~ 120 mP-V modulation ~ 0.5m

“ linear” (2D)

Petrasso et al APS 2007

0

100

200

300

400

500

0 0.5 1 1.5 2 2.5

r(m)

t (ns)

envelope of high shell density

proton arrival (a.u.)drive pulse

Radiography of a cone-in-shell capsule implosion reveals field topology and capsule compression

Fluence

Energy

14 kJ laser drive

filamentary field structures

radial focusing E-field

capsule compressedby a factor of two

cone shadow

Rygg et al Science 2008

Time-gated proton radiography of direct-drive ICF spherical implosions provides the spatial structure and time evolution of E+B fields

0 0.5 1 1.5 2Time (ns)

Drive laser

3 mm

Fluence

Seguin et al APS 2007

The reversal of proton fluence focusing indicates the direction change of a self-generated radial E field

0.8 ns 1.2 ns 1.4 ns

1.6 ns 1.9 ns 2.1ns

1015

1010

105

0

-105

-1010

-1015

0 1 2 3

Time (ns)

E

(V/m)

Data

Simulation

PRL 2008

2mm 7mm

Radiograph E+B fields generated inside Au hohlraums with protons (DD and D3He) and with alphas (D3He)

B

B

before reconnection

after reconnection

OMEGA-Scale 1.5

10 beams (1ns-square,SG4+SSD) from Cone 3 drive the hohlraum

21 beams drive the backlighter

Fields are very important for :•understanding ignition experiments at the National Ignition

Facility. •laboratory astrophysics of plasmas with lower β (~1)

0

0.4

0.8

0.0 0.5 1.0 1.5 2.0 2.5

Distance (mm)

Protons μm-2

2.6 mm

t = 0.52 ns

Observation of ~106 gauss B field and ~109 V/m E field and their temporal evolution have been made

LASNEX+LSP simulation by R. Town

MITMIT

SummaryTime-gated, monoenergetic proton radiography provides unique measurements of E+B fields in laser-produced HED plasmas

• Radiography of laser-foil interactions:

Observation generations of ~106 gauss B field and 109 V/m E field Observation of decay dynamics and instabilities of MG B field Observation of field topology change due to magnetic reconnection

• Radiography of direct-drive cone-in-shell/spherical implosions:

Observation of radial, filamentary structures with complex striations and bifurcations, of B field magnitude 0.6×106 gauss

Observation of radial E field of order 109 V/m and its direction reversal

• Radiography of laser-irradiated gold hohlraums:

Observation of ~106 gauss B field and its evolution Observation of ~109 V/m E field and its evolution