Progress in Direct-Drive Inertial Confinement FusionResearch at the Laboratory for Laser Energetics

R. L. McCroryDirectorUniversity of RochesterLaboratory for Laser Energetics

Inertial Fusion Sciencesand Applications

Biarritz, France4–9 September 2005

Significant progress continues to be made in direct-drive inertial confinement fusion research

E13806b

• Direct drive could provide a robust ignition on the NIF.

• The baseline symmetric direct-drive cryogenic D2 campaign has demonstrated target performance consistent with 1-D and 2-D hydrocode predictions.

• A new thermal transport model reconciles discrepancies among experiments.

• Polar-direct-drive (PDD) target performance is approaching that of symmetric drive.

• OMEGA EP will be completed by the end of FY07.

Summary

Collaborators

D. D. Meyerhofer, S. J. Loucks, S. Skupsky, J. M. Soures, R. Betti, T. R. Boehly, M. J. Bonino, R. S. Craxton, T. J. B. Collins, J. A. Delettrez, D. H. Edgell, R. Epstein, V. Yu. Glebov, V. N. Goncharov, D. R. Harding,

I. Igumenschev, R. L. Keck, J. H. Kelly, J. P. Knauer, L. D. Lund, D. Jacobs-Perkins, J. R. Marciante, J. A. Marozas, F. J. Marshall,

A. V. Maximov, P. W. McKenty, S. F. B. Morse, J. Myatt, S. G. Noyes, P. B. Radha, T. C. Sangster, W. Seka, V. A. Smalyuk, C. Stoeckl,

K. A. Thorp, M. D. Wittman, B. Yaakobi, and J. D. Zuegel

Laboratory for Laser Energetics, University of Rochester Rochester, NY, USA

K. A. Fletcher, C. Freeman, and S. Padalino SUNY Geneseo

J. A. Frenje, C. K. Li, R. D. Petrasso, and F. H. SéguinPlasma Science and Fusion Center, Massachusetts Institute of Technology

P. Celliers, G. W. Collins, and D. HicksLawrence Livermore National Laboratory

OMEGA cryogenic targets are energy scaledfrom the NIF symmetric direct-drive point design

E11251g

Energy ~ radius3;

power ~ radius2;

time ~ radius

103

102

101

100

0 2 4 6 8 1010–1

NIFα ~ 3

OMEGAα ~ 4

α =Pfuel

PFermi

Gain (1-D) = 45

1.69 mm

~3 μm CH

~4 μm CH

0.36 mm

0.46 mm

OMEGA: 30 kJ

NIF: 1.5 MJ

1.35 mm

DT ice

DT gas

D2 ice

D2gas

Time (ns)

Po

wer

(TW

)

E12008l

A stability analysis* defines the ignition-scalingperformance window for low adiabat implosions

*P. W. McKenty et al., Phys. Plasma 8, 2315 (2001).

• The NIF gain and OMEGA yield can be related by

σ2 = 0.06σ�<102 + σ�≥10

2 ,

where the σ�’s are the rms amplitudes at the end of the acceleration phase*.

NIF (α = 3)

1.2

1.0

0.8

0.6

0.4

0.2

0.0 0.5 1.0 1.5 2.0 2.5 3.0

σ (μm)

No

rma

lize

d y

ield

0.0

OMEGA(α = 4)

103

Ta

rge

t g

ain

100

101

102

α = 1

2

3

4

1.0 1.2 1.4 1.6 1.8 2.0

Incident laser energy (MJ)

OMEGA(α = 6)

DRACO results

1-THz, 2-D SSD with PS,1-μm-rms ice roughness,

840- outer-surface roughness,2% rms power imbalance

On-target power balance is directly determined based onrecent improvements in P510 streak camera performance

E13807a

This steak camera data will be used to improve the balance in the foot.

Shot 39421

E13398a

Scaled ignition performance on OMEGA is approachingthe predicted equivalence of high gain on the NIF

0.8

0.6

0.4

0.2

No

rmalized

yie

ld

0.0

σ (μm)

0.0 0.5 1.0 1.5 2.0

α = 4

α = 6

35713

Target offset and ice quality presently limitaccess to low σ for α = 4 campaign

DRACO

OMEGA data

1-THz, 2-D SSD with PS,1-μm-rms ice roughness,840-Å outer-surface roughness,2% rms power imbalance

Cryogenic D2 Target Performance

E13492b

Ice roughness and target offset appear to limit themeasured ⟨ρR⟩n for higher-convergence implosions.

The measured ⟨ρR⟩n is close to 1-Dfor all but the lowest-adiabat implosions

Me

as

ure

d ⟨ρR

⟩ n m

g/c

m2

0

50

100

150

0 50 100 150

1-D LILAC ⟨ρR⟩n mg/cm2

Mid-α’s

α~4 to 6α ~ 25

3796737968

200

TCC offset <60 μmand ice rms <6 μm

35713

F. Marshall et al., “Direct-Drive Cryogenic Implosions on OMEGA,”

to be published in Physics of Plasmas.

Tritium will be introduced gradually, following the successful June ’05 readiness review

E13808a

• A second FTS will be complete in 2005 for concurrent D2 cryogenic target production.

• One MCTC will be dedicated to DT operations. – At most, one DT implosion per shot day (up to 24/year).

• Potential tritium contamination of the characterization station may limit the throughput for D2 implosions.

• The initial tritium fraction will be 0.1% and be raised incrementally (×10) to reach 50:50 DT. – Layering studies can begin with 10% tritium.

• A dedicated cryogenic target test stand is being designed for advanced target development. – maintain production target throughput

The “standard” constant flux-limiter model is not consistent with experimental results

I1599

Shock velocity consistent with f = 0.06

Ablative RM perturbation evolution: f = 0.1

Δ

*V. N. Goncharov, Phys. Rev. Lett. 82, 2091 (1999).

• Perturbations are stabilized by dynamic overpressure* inside the conduction zone for kDc 1.

• kDc reaches 1 faster with an increasing flux limiter.

A new nonlocal transport model solves the simplified Boltzmann equation

I1598

• Boltzmann equation with a Krook collision model.

• A distribution function is used in electric current and heat flux.

• The electric field E is determined from the jx = 0 condition.

cosv x

fmeE

vf

f f f f meE

vf

e dxx

x x

x0

0 00

&22

22

22

+ =- - = -o o m i-p l

^ ch m#

,j e d f q m d f2x x x x3 3 2= =oo oo o# #

V. N. Goncharov, Mo 2.6

Δ

I

The new nonlocal model is in agreement with shock- velocity and perturbation-evolution measurements

I1600

A time dependent effective flux limiter is calculated from 1-D simulations.

V. N. Goncharov, Mo 2.6

Accurate shock timing is essential for ignition

I1601

• We are developing techniques to time shocks for direct and indirect drive.

– Indirect drive requirement

- first three shocks ~±50 ps (~0.3% of pulse duration)

- fourth shock ~±100 ps (~0.7% of pulse duration)

– Direct drive requirement

- two shocks ~±150 ps (~1.5% of pulse duration)

• Initial shocks will be timed with VISAR (accuracy ~20 ps).

• The final shock will be timed using x-ray radiography.

– under development (expected accuracy: 50 ~ 100 ps)

• Combining VISAR and x-ray radiography allows for absolute EOS measurements.

Simultaneous VISAR and radiography measurements provide an absolute measure of EOS

E13954

Spherical shocks minimize errors in density measurement.

VISAR-2 Shot 38808

200

0

–200

–400

µm

–10 0 10 20 30ns

ρsρs

CH Al

OMEGA laser

Al pusher

ShockUs

TC6300d

Direct drive can achieve ignition conditionswhile NIF is in the x-ray-drive configuration

23.5°30°

50°

23.5°

40°

75°

23.5°30°

50°

23.5°30°

50°

Standard pointing with

x-ray-drive configuration

Experimental and theoretical progress givesincreasing confidence in achieving PDD ignition.

F. J. Marshall FO26.2, S. Skupsky poster

Repointing for

polar direct drive (PDD) Saturn concept

Current PDD simulations show gain= 35 at 1 MJ without a Saturn ring

TC7059a

Near peak compression (8.5 ns)with perfect single-beam uniformity.

ρ

S. Skupsky poster

Spoke-mounted Saturn PDD performance is ~75% of symmetric drive

E13747d

Experimental Yields(15.3 kJ, 1 ns sq)

“Spoke” mount

OMEGA shot 39281

F. J. Marshall FO26.2

E11888e

OMEGA EP will be operational in FY07 (two beams)and ready for target physics in FY08 (four beams mid ’08)

OMEGA EP

60-beamOMEGA

• There are five primary missions

1. Extend ICF researchcapabilities with high-energy and highbrightness backlighting

2. Perform integrated fast-ignition (FI) experiments

3. Develop advanced backlightertechniques for HED physics

4. Conduct ultrahigh-intensitylaser–matter interaction research

5. High-energy-density physics research

E11888e

OMEGA EP will be operational in FY07 (two beams)and ready for target physics in FY08 (four beams mid ’08)

• There are five primary missions

1. Extend ICF researchcapabilities with high-energy and highbrightness backlighting

2. Perform integrated fast-ignition (FI) experiments

3. Develop advanced backlightertechniques for HED physics

4. Conduct ultrahigh-intensitylaser–matter interaction research

5. High-energy-density physics research

OMEGA Laser BayMainamplifiers

OMEGA EPLaser Bay

Compressionchamber

OMEGA EPtargetchamber

Boosteramplifiers

Beam 1 2

OMEGA targetchamber

G5546x

Short-pulse OMEGA EP beams can be directedeither to OMEGA or new EP target chamber

*Grating damage threshold is 2.7 J/cm2 (beam normal).

Beam 2

1 to 100 ps

2.6 kJ, 80–100 psbeam combinerlimited <80 ps

~ 2 × 1018

> 80% in 40 μm

Beam 1

1 to 100 ps

2.6 kJ, 10–100 psgrating limited*

<10 ps

3 × 1020

> 80% in 20 μm

Short pulse

Short pulse (IR)

IR energyon target (kJ)

Intensity (W/cm2)

Focusing (diam) J. H. Kelly ThF1.3J. D. Zuegel posterJ. Bromage posterB. E. Kruschwitz poster

TC5944c

OMEGA EP will have the flexibility to optimize thebacklighting of a direct-drive cryogenic implosion

*F. J. Marshall et al., Rev. Sci. Inst. 68, 735 (1997).

ΔXmotion = ν • Δt= 5 × 107 • 5 × 10–12

= 2.5 μm

Monochromatic imager(3-μm resolution)*

P target (~2.3 keV)20-ps pulse for stagnation

LiF target (~900 eV)5-ps pulse for startof deceleration

Monochromaticimager (3-μmresolution)*

200 μ

m

100 μ

m

Technique can be applied to NIF implosions.

CompressedEP beam Compressed

EP beam

OMEGA EP will test both concepts for fast ignition;two techniques have been developed to reducethe distance that an electron beam must traverse

E11710i

Channeling100-ps pulse

Igniting10-ps pulse

Light pressurecreates a channel

in the coronalplasma

~1-MeV electronsheat DT fuel to~10 keV, ~300 mg/cm2

Channeling Concept Cone-Focused Concept

Au cone

Single ignitorbeam: 10 ps

e–

Fast Ignition

A number of cone-in-shell target designs have beenimploded on OMEGA to study fast-ignition concepts

E13810

Direct-drive cone-in-shell target

Framing camera image showingthe core stagnationassembled at thetip of the rapidlyeroding cone

30º cone-in-shell target

Large cone for opticalpyrometry inside the cone

A lineout through the center of the self-emission image shows a perfectly symmetric core

E13815

• A rough estimate shows that a 0.01% mass density gold contamination would be visible in the lineout.

Logarithmic intensity scale

Lineout

The OMEGA EP HEPW beam significantly heats the fuel at peak neutron production

I1603

2-D DRACO simulationsIce roughness (srms = 4 μm)

No fast electrons With fast electrons

Increased neutron yields with the OMEGA EP beam are robust to target nonuniformities

I1602

Including alpha transport in the simulation increases the yield by over 50%.

2.5 kJ, 10 ps FWHM, 50% conv. eff.OMEGA beam illumination nonuniformity

Effect of ice roughness on neutron yield in integrated experiments

σ

Significant progress continues to be made in direct-drive inertial confinement fusion research

E13806b

• Direct drive could provide a robust ignition on the NIF.

• The baseline symmetric direct-drive cryogenic D2 campaign has demonstrated target performance consistent with 1-D and 2-D hydrocode predictions.

• A new thermal transport model reconciles discrepancies among experiments.

• Polar-direct-drive (PDD) target performance is approaching that of symmetric drive.

• OMEGA EP will be completed by the end of FY07.

Summary/Conclusions