Inertial Confinement FusionResearch at Los Alamos

National Laboratory

Steven H. BathaInertial Confinement Fusion Program Manager

Deputy Group Leader, Plasma Physics

Current Trends in Fusion ResearchMarch 7, 2007

LA-UR-07-1307

2

Collaborators from LANL include design,experiment, theory, engineering, and operations

Brian Albright, Paul A. Bradley, James A. Cobble,James Cooley, Robert D. Day, Kimberly DeFriend,

Norman D. Delamater, Evan Dodd, Valerie Fatherley,Kirk Flippo, S. Robert Goldman, Gary Grim, Hans W.

Herrmann, Nelson Hoffman, Randall P. Johnson, FrankLopez, Paul Keiter, John L. Kline, George A. Kyrala,

Shengnian Luo, Joseph M. Mack, Glenn R. Magelssen,David S. Montgomery, John A. Oertel, Harvey A. Rose,Derek Schmidt, Mark J. Schmitt, Achim Seifter, Leslie

Sherrill, Tsutomu Shimada, Damian C. Swift, MarkWilke, Douglas C. Wilson, Lin Yin

3

LANL program is small and focused on theNational Ignition Campaign• Concentrate on

– High-leverage areas– LANL strengths– Cross-cutting applicability to HED physics

• Physics areas:– Laser-plasma interaction - more efficient energy coupling– Ablator materials (laser-based material loading) - optimize designs– Symmetry (“symergy”) - correlate symmetry with yield

• Technology areas:– Trident laser - multi-user facility - supports many different programs– Be capsule machining - risk mitigation capsule material

• Neutron diagnostics– Neutron imaging system - ultimate measure of symmetry– Gamma bang time - measure absorbed energy

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Outline

• TRIDENT laser laboratory

• Laser-plasma interaction theory, modeling, andexperiment

• Symergy

• Materials research

• Target fabrication, machined Be capsules

• High-energy-density physics research

• Neutron diagnostics

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• Several hundred joules in each of 3 beams

• 8-10 shots/day

• 1st, 2nd, 3rd, and 4th harmonic

• Single hot spot diagnostic beam

• Pulse widths sub ps to > 1 µs, flexible pulse shape

• Broad range of optical and x-ray diagnostics

• Flexible user environment

Trident is an intermediate-scale laserfacility providing flexible user environment

Trident has hosted over 170 different usersfrom 32 institutions in the past 13 years

0

0.2

0.4

0.6

0.8

1

1.2

0 1000 2000 3000

Re

lative

P

ow

er

Time (ps)

HeatingThomsenScattering

Probes

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TRIDENT is a very versatile facility enablingscience, technology & technique development

0

100

200

300

400

500

600

700

800

En

erg

y (J

)

Pulsewidth100 fs 1 ps 1 ns 1 µs

TEX Goal

527 nm

1054 nm

BoostTHz EMP

Fast Ignition Ion Generation

X-Ray RadiographyProton Radiography

Detector Development LPI SSAA Program

X-Ray Generation Diagnostic Development

Dynamic Materials Properties

Dynamic Materials PropertiesFlyer-Plate DriveSNM Properties

• Pulse length variable over 6.5 orders of magnitude

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Trident facility has 2 target chambers & manydiagnostics in place

• South target chamber - elliptical shape, lots of room

• North target chamber - sphere; TIM attached

• West target chamber - being designed– Optimized for short-pulse experiments - 12 sided, cylindrical,

lots of access

• Multiple target chambers allow– Two experiments on same laser pulse– Flexible set up - choose optimal geometry for physics– Efficient experimental preparations (parallel work)

• Full range of laser diagnostics on every short-pulseshot

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Trident South target chamber providesflexible “hands-on” experimental space

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Trident North target chamber provides compatibleport configurations for NIF & Omega diagnostics

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A variety of diagnostics are standard onTRIDENT

• Streak cameras• Gated imagers• Crystal spectrometers• Grating spectrometers• Pinhole cameras• Microscope• CCD cameras• Full darkroom services

– Film scanning– Image plate scanning– CR-39 scanning

• Spectrometers• X-ray and optical

photodiodes coupledto high-speeddigitizers

• Backscatterdiagnostics

• CCD cameras• Point and line-imaging

interferometers(VISARs)

• Streak cameras• Short pulse

autocorrelator

X Ray Optical MeV Particles• Thomson parabolas• Multi-layer RCF film• CR-39 detectors

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Trident enhancement will increase laser energyin short-pulses

• Increased energy in short-pulse beam to > 200 J

• Added vacuum compressor with large dielectricgratings

• New beam transport, active beam quality control withadaptive optics, beam diagnostics

• High-quality front-end

• Schedule for completion in early summer

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Mitigation of laser-plasma instabilities (LPI)improves laser-hohlraum coupling

• Integrated program of theory, simulation, & experiment

0 10 20 30 40

2.0

2.5

3.0

3.5

4.0

Ab initio1D to 3D PICSimulations

FundamentalLPI Theory

Reduced-PhysicsNonlinear Models

Experiments atOmega, Trident, LULIfor Model ValidationLIP + Lasnex

LPI linear estimates & Nonlinear FOMs

pF3D: Multi-DNonlinear Fluid Code

LPI PredictiveCapability

ReducedLPIICF

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Preliminary VPIC 3D LPI simulation showsgrowth of filamentary structures

Simulation parameters:5.75x108 cells1.8x1010 particles32 particles/cell1008 processors onLightning/BoltTe=700 eV, λDe=0.037 µmI0=1x1016 W/cm2, λ0=527 nm

Simulation domain

Longitudinal E field

18 µm90.4 µm

18 µm

Shaded regionshown below

laser

ωpet=842 ωpet=1894Isosurfaces at Ex= +/- 0.025 Isosurfaces at Ex= +/- 0.03

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Short-pulse, single-hot-spot experiments givefundamental understanding

• Particle-in-Cell (PIC) codes only simulate a few ps

• SRS gain time is of order a ps

• “Single-hot-spot” (SHS) experiments use a very cleanoptical beam that mimics a single speckle in asmoothed laser beam

• “Short-pulse” experiments use pulses of order ≈ 5 ps

• High-quality diagnostics– Electron temperature and density, reflectivity, transmission

• Combining these elements gives a clean quantitativetest of fundamental modeling of SRS

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Image of gas-jet plasma

Clean experiment will validate reduced modelsuseful for the ignition design process

• Once the simulations are validatedquantitatively, the codes can beused to develop predictive modelsfor SRS

• The predictive models will provideNIF ignition designers the toolsneeded to find regimes thatminimize SRS

• Gas-jet plasma provides areproducible, clean, well-characterized plasma

• Thomson scattering measureselectron temperature and densityon every shot

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Experimental setup utilizes Trident versatility

BackscatterDiagnostics

Oscillator527 nmHeater Beam

KDP crystal1.053 µm to ~527 nm

Broadband beam splitter

Timing mirror

F4.5 lens

Gas jet Amp

Single Hot Spot

5 ps

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Now have detailed measurements of thedependence of SRS on kλDe and intensity

Density scaling of SRS reflectivity

Io = 1.6 - 2.2 x 1016 W/cm2

Density increases with wavelengthkλD decreases with wavelength

Intensity scaling of SRS reflectivity

Saturation of SRS occurs nearIo ~ 3 x 1016 W/cm2

Sharp onset

SaturationkλD

• In a regime that can be modeled quantitatively

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Transmitted beam distribution acts as a probe ofdensity fluctuations caused by the heater beam

No Plasma He/H PlasmapF3D simulationTransmitted beam distribution

plasmaheater beam density fluctuations arestatic on 5-ps short pulse timescale

f/4.5 beam cone

single hotspot

transmittednear-fielddistribution

diffuserscreen

horizontalstriations kX(k0/2F)

Ed W

illia

ms

(LLN

L)

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Mitigation: Addition of high-Z dopant decreasesStimulated Raman Scattering (SRS)

Theory/model predictions Omega results showingreduced SRS with Xe

• Adding a high-Z dopant (Xe) decreases the thermal filamentation threshold• More filamentation increases “beam spray,” reducing the speckle/correlation length and resultant SRS gain length

IncreasedIncreasedHigh-ZHigh-Zdopantdopant

Wavelength (nm)

Tim

e (n

s)

0% Xe

400 450 500 550 600 650

2.0

1.5

1.0

0.5

0.0

2.0

1.5

1.0

0.5

0.0

9% Xe

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Integrated designs of hohlraums & capsulesenables informed decisions on facility hardware

• Beam pointing study showedthat P2 asymmetry was reducedand yield increased as pointingwas varied

• Also studied varying beam spotsize for phase plate design

• These two problems coupled

• Currently optimizing inner-conespot size, LEH size, gas-fillpressure, and 4th pulse

• Designing 96-beam experimentsfor FY08

Yie

ld (M

J)

cmOuter-Cone Pointing

(inner cone fixed)

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Symergy experiments will validate connectionbetween symmetry & performance

• Integrated design/experimental effort tomeasure symmetry, energyabsorbed, and LPI on sameshot

• Average asymmetry to zero aswall motion changes symmetry

• Intentionally start withasymmetry

Laser and entry hole

Imploding Capsule

0 ns

.7

1.4

2.1

5.0

5.7

LANL Large FormatCamera record

Imploded core emission

Au Hohlraum stagnation

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Understanding, to a fine degree, berylliumproperties is necessary for ignition

• Choosing a robust ignition configuration requires detailedknowledge of material response, particularly melt pressure

• Materials with grains can cause shock roughness– Degrade implosion by enhancing mixing

Dynamic ellipsometry showing optical detection of bandstructure effect of a phase change (melting) in Sn through LiFrelease window.

X-ray diffraction from Ga crystal showing detection of a phasechange (melting). Shock: laser ablation.

Phase changes

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Advanced target fabrication is important toenable the experiments shown• Careful experimental design

• Translates into complex target

Partnership with General Atomics– Production performed by GA– Design & assembly by LANL

TCCP6

P7

TIM5: XRFC2

H16I: DANTE

P2B: HENWAY

TIM6: XRFC4

TIM4: LFC

TIM3: XRFC1

QXI,2XLaserSpots

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LANL provides a risk-mitigation path forignition through Be capsule machining

• Machined capsules are near NIF roughness specs– Other manufacturing techniques not yet proven

• Key issue is the joint where two hemispheres meet -causes defect hydro

MachinedCapsuleJoint

Glue Voids inPlane of Joint

175-µm WallThickness

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How do you measure the DT ice layer qualityinside an opaque capsule?

• Intensity modulationsat edges caused byphase gradient can bedeconvolved

• Detection & the effectof voids & cracksinside the ice is thecurrent area ofinvestigation

D-T ice layer

Fill tubeGlue joint

• X-Ray Phase Contrast Imaging developed atLANL in response

In collaboration with LLNL

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Planar fill tube experiment tests hydrodynamicinstability modeling in ICF ignition designs

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• Capsules require a gasfill tube to simplifycryogenics

• Hole in shell creates a jet(defect hydro) that coolsthe imploding gas anddegrades the efficiencyof the capsule

• We measured the amountof mass ejected

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Experiment measures jet mass and compares tosimulations

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50 mg/ccCRF foam

200 µm thickBeCu(3%)washer

100 µm thickBeCu(3%) ablator

20-100 µmdiameter hole

• Gold hohlraum is heatedto 200 eV bu the laser drivebeams• Radiation ablates one sideof the Be disk launching ashock• Radiation travels down thehole, ablating Be materialfrom the sides of the walls• The shock breaks into thehole jetting more Bematerial forward. Thisprocess forms the Be jetthat is observed in theseexperiments.• Jet mass inferred fromradiographs•

Hohlraum

Laser DriveGold Cone(diagnostic shield)

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Including a small amount of preheatis required to match observations

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177 µm230 µm

330 µm

0 µm

False color radiograph

Pedestal

Jet

Shock

Simulated Radiograph

Jim

Elli

ott (

LLN

L)

• 50 micron diameter hole• 15 ns after drive• 0.175 eV preheat in simulations

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Jet mass prediction from simulations fall withinexperimental uncertainty

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• Results are preliminary and moreanalysis is being carried out toconfirm values and error bars

• 190 eV simulations (in red) didnot have all the required physics

• 200 eV simulations (in blue) aremost current

• Simulations of 40 microndiameter hole appear to predict amuch smaller jet mass thanmeasured

Hydra Simulations By Jim Elliott (LLNL)

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Je

t M

as

s (

mic

rog

ram

s)

Hole Diameter (cm)

Feb. 06 - shot 4271340 micron diameter hole

Area BL -2.8 keV6.5 ns

Aug. 06 - shot 4466250 micron diameter hole

PPBL -4.3keV~15 ns

Aug. 06 - Hydra simulation50 micron diameter hole

200eV, 4 ns temp source scaled by 89.97% 14.9 ns

Hydra simulations190eV, 1 ns temp source

15 ns

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Moreover, how does the presence of preheat affect the initialconditions of these defects and surface roughness?

Off-Hugoniot experiments study the physics ofdefects and small-scale mixing in ICF capsules

Beryllium capsules start astwo hemispheres that arewelded together.

Manufacturing defects at the gap canlead to mixing that degrades capsuleperformance

Mixing seeded by surfaceroughness mixes hot ablatormaterial with cold fuel makingtarget harder to compress

Rough surface can seed mixDT Ice

Be Shell

Double-shell targets represent an alternativeto cryogenic ICF designs and will likely beused in uses of ignition campaigns on NIF

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Principal Objective: Develop a platform to studythe evolution of defect-driven hydrodynamics

• Study evolution ofheated andindependentlyshockedhydrodynamicsystems

• Experimentprogresses in 4phases:

HeatingShockBacklighterDiagnostic

Backlighter

BafflingCone

Ta ApertureThin SnCoating

Beryllium Housing

EpoxyAblator

Epoxy/FoamPackage

HeatingBeams

Shock DriveBeams

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43731

42009 4201842005

43729

Platform has proven versatile, yielding highquality data under differing conditions

Cold Shocked

Heated & Shocked

Heated Discs Heated Gaps

Heated & Double Shocked

Shock Drive

Shock Drive

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Highly resolved density profiles provide tightconstraint for PETRA-NYM EoS models

With the EoS model constrained, PETRA-NYM accuratelycaptures the key physical features for preheated defects

PETRA-NYM quantitatively matches horizontal expansion.Vertical evolution is qualitatively similar.

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Simulations show dynamic density perturbationsaffect material flow and shock deformation

19.5 ns 17.5 ns 14.0 ns

Shock Front

Abla

tor R

emna

nts

Rare

fact

ions

Transmitted Shock

Epoxy

FoamShoc

k De

form

atio

n

Low Pressure Region

Material in low-pressure areas is swept out by main shock creating a highdensity island in defect center. Island width grows since residual density

gradients continue to evolve as main shock propagates through

Island

Defe

ct S

ize

Orig

inal

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Defect-driven hydrodynamic experiments testmodeling and margins of ignition capsules

• These experiments study the impact ofmanufacturing defects on ICF capsule performanceby providing quantitative data for hydrodynamicscode validation in complex systems

• The presence of heated defects results in dynamicdensity variations that adversely affect shockmorphology

• The spatial extent of these variations are much largerthan the initial defect

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Neutron imaging system will be the second NIFdiagnostic built by LANL• Neutron imaging will be the main

“failure” diagnostic on NIFignition shots

• Development of multiple-aperturepinholes– Increase signal-to-noise to reach

high resolution– Needed to measure down-scattered

neutrons (<1% of primary flux)

• LANL will design & build portionsof this diagnostic for NIF

Neutron Imaging is an extremelychallenging problem

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• Reduces uncertainty in a key modeling parameter

• Burn-history measurement can be made with eitherfusion neutrons or fusion gamma rays

• Neutrons are slow and affected by path

• Gamma rays travel at speed of light

Time of maximum burn is a stringent measureof capsule absorbed energy

γ(16.7 MeV)(12 MeV?) + 5He

0n1(14.1 MeV) + 4He

0.99999

~10-5

D + T

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Measure the gamma ray by converting to anelectron

• Then record the Cerenkov radiation from electron

Be Converter

W shielding

Secondary mirror

Primary mirror

DetectorAl chamber

CO2

Burn-history measurements can be madewith either fusion neutrons or fusion γ rays.

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Gas-Cerenkov Detector has same precision ascurrent diagnostics & better time resolution

• Compare GCD with neutron temporal diagnostic - standarddiagnostic but not scalable to NIF

• Ultimate goal is a full-coverage reaction history diagnostic for NIF– Critical for ignition capsule performance assessment

• Essential collaboration with AWE, NSTec, LLE, LLNL

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Summary

• Providing key contributions to the National IgnitionCampaign

• Our program is focused on exploiting– LANL strengths– Key areas for ignition– Leveraging towards the future

• Concentrating on– Laser-plasma interactions– Ablator material science– Symergy– Defect-driven hydrodynamics– Neutron diagnostics– Trident laser laboratory now being upgraded to 200 TW