Driving Gigabar Shocks With High-Power Lasers and Their Applications to Shock Ignition

W. TheobaldUniversity of RochesterLaboratory for Laser Energetics

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3000

200

400

600

800

1000

400

Distance (nm)

Pre

ssu

re (

Mb

)

500 600

Backsideof CH foil

Hot-electronshock

Hydrodynamicshock

Laser

Workshop on Scientific Opportunities in High-Energy-Density Plasma Physics

Washington DC25–27 August, 2008

FSCCollaborators

R. Betti,* C. Stoeckl*, K. S. Anderson,* T. R. Boehly, J. A. Delettrez, V. N. Goncharov, V. Yu. Glebov, R. L. McCrory, D. D. Meyerhofer,*

P. B. Radha, T. C. Sangster, W. Seka, A. A. Solodov*, B. Yaakobi, and C. D. Zhou*

Laboratory for Laser EnergeticsUniversity of Rochester

*also Fusion Science CenterUniversity of Rochester

J. A. Frenje, C. K. Li, and R. D. PetrassoMassachusetts Institute of Technology

Cambridge MA

L. J. PerkinsLawrence Livermore National Laboratory

Livermore, CA

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High-power laser facilities such as OMEGA EP and the NIF are ideal for the generation of gigabar shock waves

E17112

Summary

• Gbarshockwaveshaveimportantapplicationsforinertialconfinement fusion and for studying matter under extreme conditions.

• Shockignitionusesastrong,lateshockwavetoaugmentthecompression and bring the hot spot over the ignition threshold.

• OMEGAEPwillbeusedtostudyultrastrongshocksgeneratedby short-pulse, IR-beam-produced hot electrons.

• OMEGAEPwillgeneratestronghydrodynamicshockswithhigh-intensity UV laser beams.

• Integratedshock-ignitionexperimentsareplannedonOMEGAusing 40 + 20 beams.

Shock ignition uses a late shock to augment the compression of the central hot spot above the ignition threshold

E16323a

The ignitor shock wave significantly increases its strength as it propagates through the converging shell.

Time

Powerspike

Las

er p

ow

er

Spike shock wave

Returnshock

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20

15

10

Po

wer

(T

W)

5

0–1 0 1

Time (ns)

Laser pulse shape

2 3 4

0.25

0.20E

xper

imen

tal

GtR

H(g

/cm

2 )

Calculated GtRHn (g/cm2)

0.10

0.15

0.10 0.15 0.20 0.25

0.20Secondary D3He proton spectrum

0.15

0.10

0.05

0.00

No

rmal

yie

ld (

MeV

)

Energy (MeV)0 5 10 15 20

Yn = 2±0.2 × 109

Yn = 8±0.8 × 109

Detectorcutoff

1-Dsimulation

GtRH = 220±20 mg/cm2

CH

390 nm

40 nm8 – 25 atm

D2 gas

Low-implosion-velocity CH targets filled with D2 have produced total areal densities of ~200 mg/cm2

E16830a

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Hot electrons of moderate energies produced duringtheshockspikecanbebeneficialtoshockignition

TC7870

Hot e–withMaxwellianThot = 150 keV, Ehot = 25% of spike energy, treated using a multigroup diffusion model*

10.00

2

3

1

4

5

0

40

60

20

80

100

10.5 11.0

Time (ns)

Inte

nsi

ty (

1015

W/c

m2 )

tR

(m

g/c

m2 )

10.20

10

40

30

20

50

60

10.4 10.6

Shock-launching time (ns)

Gai

n

Without hot e– With hot e–

tR

tR range of 100 KeV e–

ILaser

Shock-ignition targetwith 350-kJ total energy

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*J. Detettrez and E. B. Goldman, LLE, Univ. of Rochester, Rochester, NY, LLE Report No. 36 (1976).

0

800

600

400

200

1000 Parallel e-beam

Shockfront

Backsideof CH foil

Pre

ssu

re (

Mb

)

Laser

00

10

20

30

40

50

60

70

Shockfront

Backsideof CH foil

250 500Distance (nm)

Pre

ssu

re (

Mb

)

750

0 200 400Distance (nm)

600

Laser

Shock-driving100-ps IR beam

Plasma generatorUV beam

100-nm diam

Plasma generatorUV beam

600 nm

CH

VISARDoppler

interferometer

3000 nm

Divergent e-beam (26°)

OMEGA EP is an ideal facility to study ultrastrong shocks generated by IR-beam-produced hot electrons

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• Long-scale-lengthplasma(mm).

• ModerateIRintensityof3× 1017 W/cm2.

• OMEGAEPbeamwith2.5kJ, 10% CE into hot electrons.

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0

500

400

300

200

100

600 1 × 1016 W/cm2

Shockfront

Backsideof CH foil

Pre

ssu

re (

Mb

)

Laser

0

1200

900

600

300

1500

Shockfront

Backsideof CH foil

Pre

ssu

re (

Mb

)

0 200 400Distance (nm)

600

0 200 400Distance (nm)

600

Laser

600 nm

Three overlappedshock-driving1-ns UV beams

CH

VISARDoppler

interferometer

Plasma generatorUV beam

1 × 1017 W/cm2

3000 nm

Even stronger shocks can be generated hydrodynamically with high-intensity UV laser beams

E17114

• Long-scale-lengthplasma(mm).

• Threebeamsareoverlappedwithspotsizes varying between 100 to 300 nm.

• Beamenergyofupto~2 kJ in 1 ns.

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A hydrodynamic simulation including fast-electron generation shows the formation of two strong shocks

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• Long-scale-lengthplasma(mm).

• ThreeoverlappingUV OMEGA EP beams, E = 7.5 kJ (1 ns), 1017 W/cm2.

• 10%CEintoGEH ~ 150 keV hot electrons.

3000

200

400

600

800

1000

400

Distance (nm)

Pre

ssu

re (

Mb

)

500 600

Backsideof CH foil

Hot-electronshock

Hydrodynamicshock

Laser

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The shock pressures are inferred from shock-velocity measurements with a VISAR system

E17116

23°

48°

Probe laser

1 2

f/3

VISAR’s

Temperature calibrated self-emissioncamera (SOP)

CH/SiO2

0 5

Time (ns) Time (ns)

–400

–200

0

200

Lat

eral

po

siti

on

(n

m)

0 52 4311 2 3 4

CH SiO2SiO2CH

Catch upCatch up

BreakoutBreakout

VISAR Self-emission

~v pstrong

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Integrated shock-ignition experiments will study the effect of fast electrons on the hydrodynamic performance of imploding shell targets

E17117

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Integrated shock-ignition experiments are planned on OMEGA using 40 + 20 beams.

Laser

Criticalsurface 1016 to 17 W/cm2

Laser

Hot e–

Hot e –

Laser

Laser

01012

1013

1014100

Are

al d

ensi

ty

150

200

250

50

0

1015

Drive

~100-keVstopping range

Fast-electrongeneration

1016

1 2Time (ns)

Las

er in

ten

sity

(W

/cm

2 )

3 4 5TargetTargetHot e–

• Sphericallysymmetricillumination.

• Moderate-energyhotelectrons(100 to 300 keV) are generated at the end of the implosion.

• Shellarealdensityishighenoughtostopthehot electrons.

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E17112

Summary/Conclusions

High-power laser facilities such as OMEGA EP and the NIF are ideal for the generation of gigabar shock waves

• Gbarshockwaveshaveimportantapplicationsforinertialconfinement fusion and for studying matter under extreme conditions.

• Shockignitionusesastrong,lateshockwavetoaugmentthecompression and bring the hot spot over the ignition threshold.

• OMEGAEPwillbeusedtostudyultrastrongshocksgeneratedby short-pulse, IR-beam-produced hot electrons.

• OMEGAEPwillgeneratestronghydrodynamicshockswithhigh-intensity UV laser beams.

• Integratedshock-ignitionexperimentsareplannedonOMEGAusing 40 + 20 beams.