R. L. McCroryProfessor of Physics and AstronomyProfessor of Mechanical EngineeringDirector, Vice Provost, and Vice PresidentUniversity of RochesterLaboratory for Laser Energetics

Fusion Power Associates Meeting

Washington, DC5–6 December 2012

Progress Toward Polar-Drive Ignition for the NIF

0 50 100 150 200 250 300 350

tR (mg/cm2)

Neu

tro

n y

ield

(×1

013 )

10

1

0.1

1.0

0.5

0.2

0.1

0.05

0.020.01

Si-doped CD ablatorPure CD ablator300-mg series (2009)

EquivalentITFx

I2064

Significant progress toward demonstrating direct-drive ignition on the NIF is being made

• Polardrive(PD) will allow for direct-drive–ignition experiments at the National Ignition Facility (NIF) in the x-ray-drive configuration

• OMEGAdirect-drivecryogenictargetimplosionsaredefiningtheignitiondesign space

• Performancecontinuestoimprove

– the yield and ion temperature increase with implosion velocity up to 3.8 × 107 cm/s (maximum to date)

– the measured areal density agrees with 1-D predictions for adiabats >2.5

– Px increased to ~3.0 atm-s

– a NIF-scaled experimental ignition threshold factor has increased to ~0.15

• Progresstowarddevelopingpolardriveisongoing,includinginitialNIF PD experiments

LLE is making progress toward demonstrating ignition hydro-equivalentperformanceonOMEGA.

Summary

Collaborators

R. Betti1*, T.R. Boehly1, D.T. Casey2, T.J.B. Collins1, R.S. Craxton1, J.A. Delettrez1, D.H. Edgell1, R. Epstein, J.A. Frenje2, D.H. Froula1, M.Gatu-Johnson2,V.Yu.Glebov1,V.N.Goncharov1, D.R. Harding1,

M. Hohenberger1, S.X. Hu1, I.V. Igumenshchev1, T.J. Kessler1, J.P. Knauer1, C.K. Li2, J.A. Marozas1, F.J. Marshall1, P.W. McKenty1, D.D. Meyerhofer 1*,

D.T. Michel1, J.F. Myatt1, P.M. Nilson1, S.J. Padalino3, R.D. Petrasso2, P.B. Radha1, S.P. Regan1, T.C. Sangster1, F.H. Séguin2, W. Seka1, R.W. Short1, A. Shvydky1, S. Skupsky1, J.M. Soures1, C. Stoeckl1,

W. Theobald1, B. Yaakobi1, and J.D. Zuegel1

1Laboratory for Laser Energetics, University of Rochester2Plasma Science and Fusion Center, Massachusetts Institute of Technology

3StateUniversityofNewYorkatGeneseo

*also Depts. of Mechanical Engineering and Physics and Astronomy, University of Rochester

Direct drive is a true alternative to indirect drive

I2004a

• Directdrivecouplesmoreenergytothecapsule

– provides higher margins

• Theconcepthasbeenvalidatedthroughdecadesofresearch,primarilybyLLEonOMEGA,withcontributionsfromNRL

• Shockignitionprovidesanadditionaldirect-driveoptionwiththe possibility of significantly higher gain

– less validated to date

Direct-drive ICF is a viable ignition alternative for the NIF

E18400l

• Directdriveispredicted to couple 7 to 9× more energy to the compressed core than indirect drive

• 2-Dsimulationspredict gains of ~50 on the NIF with symmetric irradiation

• CryogenictargetimplosionsarestudiedonOMEGAat~1/4 of the NIF target scale

– R ~ (EL)1/3

• LLEisdevelopingpolardrive to allow for direct-drive–ignition experiments while the NIF is configured for x-ray drive

0

1

0

2

3

2 4 6 8Time (ns)

Three-picket NIF design

Po

wer

/bea

m (

TW

)

10 12

160 nm DT

37 nm CH

DT gas

1700

nm

Gain1-D= 48

75°

40°

23.5°30°

50°23.5°

Repointing for polar drive*

2-D simulations predict polar-drive ignition on the NIF when appropriate beam smoothing has been added.

The in-flight aspect ratio and adiabat determine the target stability and areal density

TC10126

• In-flight aspect ratio (IFAR): Ratio of the implosion radius to the shell thickness at 2/3 of the in-flight radius

– IFAR determines of the amplitude of the Rayleigh–Taylor (RT) modulations that disrupt the implosion

– the 1-D minimum energy for ignition, Emin ~ 1/(IFAR)3

• Adiabat: Mass-averaged adiabat contributing to the stagnation pressure

– the adiabat determines the target compressibility and the RT growth rate

IFAR2/3 = R2/3/D2/3

. /g cmadiabat

pressure MbarPP

2 2f 5 33t= = ^

^hh

Symmetric direct-drive–ignition designs* can be scaled forhydrodynamicequivalenceonOMEGAscale

TC10256c

Hydrodynamic scaling Direct-driveNIF 1.8 MJ*

3.6 mm

0.86 mm

OMEGA 26 kJ

Scale 1:70in energy

Capsule radius ~ ELShell thickness D ~ ELLaser power ~ ELPulse length ~ ELMass fuel ~ EL

1/3

1/3

1/3

2/3

Hydrodynamic similarity is ensured by keeping the implosion velocity, adiabat, and laser intensity the same at the two scales.**

*V.N.Goncharovet al., Phys. Rev. Lett. 104, 165001 (2010).**R. Betti presented at the 24th IAEA Fusion Energy Conference, SanDiego,CA,8–13October2012.

OMEGAdirect-drivecryogenictargetimplosions are defining the NIF PD design space

TC10127

• Thetargetadiabatischangedwith

– picket-pulse spacing and heights

– step on main pulse rise

• TheIFARisvariedthroughthe

– ablator thickness

– ice thickness

• Theimplosionvelocityisvariedthrough the

– target mass

– laser intensity

0.3

0.2

0.1

0.00 1 2 3 4

Target design

430 nm

Ablator

DT ice

D2/DTgas

Po

wer

(T

W)

Time (ns)

Cryogenic target implosions are validating the physics models used in simulations.

~P YR . .meas

0 6 0 34x t^ h

OMEGAcryogenic-DTimplosionscanaccessthedesignspace for ignition on the NIF

E21735a

• Theprimarydesignparametersintheradiation–hydrodynamic models are

– laser intensity: IL ~ 0.8 to 1 × 1015 W/cm2

– shell velocity at the end of acceleration: Vimp ~ 2.5 to 3.8 × 107 cm/s

– mass-averaged adiabat contributing to the stagnation pressure: a ~ 1.5 to 4.0, where a = P/Pf = P/2.2 t5/3

– in-flight aspect ratio: IFAR ~ 10 to 25, where R/Dr is evaluated at 2/3 the initial radius

30

25

20

101 2 3 4

15

2012 implosion database

370

Polar-drive–ignition designs

Hig

her

sta

bili

tyIF

AR

Adiabathigher stability

Ourdatabaseincludesonlyphysicsquality shots.

The (1-D) predicted implosion velocity is confirmed by the measured burn history

TC9778e

To match the data, the 1-D design code LILAC incorporates nonlocal thermal transport1 and a stimulated Brillouin scattering (SBS) model2 to account for cross-beam energy transfer (CBET).

Without CBETWith CBET

1021

Time (ns)

1020

1019

10183.2 3.4 3.6 3.8

Measurement

Neu

tro

n r

ate

(1/s

)

A 10% changein velocity is atiming shift of 150 ps

The observed shift in the 1-D bang time shows the importance of including the CBET model in the design code.

1V.N.Goncharovet al., Phys. Plasmas 15, 056310 (2008).2I. V. Igumenshchev et al., Phys. Plasmas 19, 056314 (2012).

Cryogenic target performance is parameterized by the ratio of the neutron yield to that predicted by 1-D simulations [yield over clean (YOC)]

TC10123

The 1-D simulations include all of the known physics with no adjustable “knobs.”

IFAR < 22

24

22

20

18

16

14

1.5 2.0 2.5 3.0 3.5

Adiabat

IFA

R

Map of Yexp/Y1-D (YOC)Symmetric point design

25

20

15

10

5

00 1 2 3 4

YO

C (

%)

Adiabat

IFAR $ 22

YOC (%)

>22.520.0 to 22.517.5 to 20.015.0 to 17.512.5 to 15.010.0 to 12.57.5 to 10.0<7.5MeasuredYOC

The neutron yield and ion temperature increase with implosion velocity

E21739a

Ignitionrelevant

2 3 4

1014

1013

1012

Vimp (×107 cm/s)

2012 implosion database

Yie

ld

2

2

3

3 4

Vimp (×107 cm/s)

2012 implosion database

T i (k

eV)

1-D

Measured

1-D

MeasuredIgnitionrelevant

Ignitionrelevant

Ignitionrelevant

The measured tR performance is ~1-D for adiabats > 2.5 and IFAR < 20

E21738

0.01 2 43

0.2

0.4

0.6

0.8

1.0

Adiabat

tR

/tR

1-D

0.010 3020

0.2

0.4

0.6

0.8

1.0

IFAR

tR

/tR

1-D

2012 implosion database 2012 implosion database

Offsets < 20 nmIce < 1.5-nm rms

Note: For most points, the measured tR is an average inferred from two independent measurements.

The ICF Lawson criterion can be used to connect the design parameters to observables

E21737

• Lawsoncriterionisdefinedas| = Px/Pxign > 1

• Ameasurableform*of| is:

| ~ (tR)0.61 × (0.24 Yn/Mfuel)0.34 , where tR is in g/cm2, Yn is in units of 1016, and Mfuel is in mg

• Avalueof| = 0.16 is needed to demonstrate hydro-equivalent ignitionperformanceonOMEGA*

• ThiscorrespondstoatR of ~300 mg/cm2 and a yield of ~4 × 1013

• ThebestimplosionsonOMEGAtodategiveavalueof| = 0.09, where tR ~ 160 mg/cm2 and Y ~ 2.1 × 1013

*R. Betti presented at the 24th IAEA Fusion Energy Conference,SanDiego,CA,8–13October2012.

Hydrodynamic scaling suggests less yield degradation due to nonuniformities on NIF

TC8660a

• TherequiredYOConOMEGAisdifficulttoestimate. Use simple clean volume analysis:

D D=- - –R3 RT1R DR ~R GRT RT0vD G GRTNIF

RT. X

RT spike amplitude Growthfactor Hydro-equivalency

– –YOC 1 1 YOCE

E/

/NIFNIF

NIFL

L

0

01 3

1 33

.v

vX

XXf ^bp h l

R

T

SSSS

V

X

WWWW

Initial seed

YOC’sareexpectedtobehigherontheNIFbecauseof a significantly larger clean volume fraction.

R3-D

Hot spotCold

Shell

R1-DGvoH ≈ 0

• Fusionreactionsoccurin the clean volume (red) YOC

YY

RR

1 D

3 D3

n1 Dn3 D.=

-

--

- f p

Implosion performance can be parameterized by an ignition threshold factor

TC10131a

• LLNLderivedanExperimentalIgnitionThresholdFactor(ITFx)

– ITFx (ID) = (Y/3.2 × 1015) × (DSR/0.07)2.3, where tR (g/cm2) = 21× DSR (%)

– ITFx = 1 corresponds to a 50% likelihood of ignition

– ITFx ~ (Px)3

• ThisformulacanbescaledtoOMEGA(X) energies*

– ITFx (NIF equivalent) = ITFx (IDX) × (ENIF/EX)1.28 × (Mfuel NIF/Mfuel X)

– ENIF = 1.8 MJ, EX = 25 kJ, Mfuel NIF = 0.17 g, Mfuel X = 0.02 g

S. W. Haan et al., Phys. Plasmas 18, 051001 (2011). * C.D. Zhou and R. Betti, Phys. Plasmas 15, 102707 (2008); R. Betti et al., Bull. Am. Phys. Soc. 54, 219 (2009).

†

× YOCNIF/YOCX

TheOMEGAITFxhydro-scaledtotheenergyavailableon the NIF exceeds 0.1

TC10124c

ITFx (NIF Equiv) = 4050 * (Y/3.2 × 1015) × (tR/1.5 g/cm2)2.3

Performance is independent of the ablator indicating that imprint is not (yet) the dominant perturbation source.

0 50 100 150 200 250 300 350

tR (mg/cm2)

Neu

tro

n y

ield

(×1

013 )

10

1

0.1

1.0

0.5

0.2

0.1

0.05

0.020.01

Si-doped CD ablatorPure CD ablator300-mg series (2009)

EquivalentITFx

Core x-ray emission suggests that target performance degradation is caused by ablator carbon mix in the core

E21741a

By raising the adiabat, the shell is stabilized, and mix is reduced even at high implosion velocities.

160

120

80

40

00.0 0.5

1-D calculations Experiment

MixFit: Y0.57

1.0

X-r

ay c

ore

em

issi

on

4 to

7 k

eV (

arb

itra

ry u

nit

s)

Yield (×1014)

3

2

1

01.5 2.0 2.5 3.0 3.5N

orm

aliz

ed e

mis

sio

n/Y

0.57

Adiabat

Simulation

Further improvements in cryogenic target performance are expected over the next year

TC10132a

• Isolatedsurfacedebrisonthetargetappeartobelimitingtheimplosionperformance

– a significant engineering effort is underway to remove the defects

– a2011shotseriesshowedimprovedYOCwhenfewerdefectswerepresent

• Theeffectsofcross-beamenergytransferarebeingunderstood

• DopingtheouterpartoftheablatorwithSiorGewillreduceimprinting and RT growth

Cryo-2093-1664Cryo-2093-1664

DendriteCondensates

Cryo targetimage

0.5

1.0

1.5

2.0

0.020 40 60 80 1000

Yie

ld (

×10

13)

Offset (nm)

Before May ’11May ’11–Apr ’12Aug ’12

LLE is working to demonstrate ignition hydro-equivalent performance in 2013

E21754a

• Eliminatingtheisolatedtargetsurfacedefectswillmean

– lower-adiabat implosions (higher tR) with improved shell stability

– higher-velocity/IFAR implosions at lower adiabats

– imprint and stalk become the dominant perturbation sources

• WhileCBETdoesnotrestrictaccesstothedesignspaceonOMEGA,mitigation would provide more stability across the design space

– thicker shells could be driven to the same Vimp with the same laser energy

– mitigation may be necessary to achieve hydro-equivalent performance (should know within a year)

Improvements to the NIF PD target design have reduced the IFAR and implosion velocity

TC10134

• Anew1.5-MJNIFPDtarget design has enhanced stability

– implosion velocity 4.3 × 107 cm/s " 3.7 × 107 cm/s

– in-flight aspect ratio 36 " 30

• 2-Dgain~70, with PD illumination only

• 2-DsimulationswithfullNIFnonuniformities are underway; expect a gain of ~30

100

50

00 50 100

r (nm)

z (n

m)

0

80

160

240

320

400

480

560

t (g/cm3)

3

4

5

11

2 (keV)2 (keV)

3

4

5

66

77

8899

Improved symmetry has been demonstrated with shimmed shells

TC10362

–10

0

10

20

–203.1 3.2 3.3

DRACO , = 4

DRACO , = 2

3.4 3.53.0

Mo

de

amp

litu

de

(%)

Time (ns)

Experiment , = 4Experiment , = 2

–10

0

10

20

–203.1 3.2 3.3

DRACO , = 4

DRACO , = 2

3.4 3.53.0

Mo

de

amp

litu

de

(%)

Time (ns)

No shim (67343)0 nm, 120 nm, 140 nm

Shimmed (67345)Experiment

500 n

m

500 nm

DRACO/Spect3D Experiment DRACO/Spect3D

Experiment , = 4Experiment , = 2

CR ~ 5 CR ~ 5

R ~ 76 nm R ~ 77 nm

Early NIF experiments will address key issues for PD ignition

TC10147a

• Thegoalisto

– demonstrate drive uniformity

– measure laser coupling

– identify and address laser–plasma interactions- longer coronal density scale lengths in NIF implosions

may result in larger effects of cross-beam energy transfer1

and fast-electron preheat from two-plasmon decay2

• TheseexperimentswillusetheexistingNIFconfiguration (phase plates and beam smoothing)

• Thedesignsuseacombinationofbeamdefocus,repointing,andindependent ring pulse shapes to achieve the required symmetry

• Thefirstshotwillbeperformedthismonth

The primary goal of early NIF experiments is to predictably change implosion symmetry

TC10148

• Implosionsymmetryisvariedbychangingringenergies

Simulated x-ray self-emissionimages* (ho L 2 keV)500

500

0.2

0.6

1.0

Relativeintensity

0

0

0

–5

5Oblate

Prolate

0

2 4 6

–500

–500

y (n

m)

500

0

–500

y (n

m)

500

0

–500

y (n

m)

x (nm)

Time (ns)

P2

mo

de

amp

litu

de

(%)

20

20

40

60

4Time (ns)

Po

wer

(T

W)

6

CH

0.7 atm air1100 nm

80 nm

EL ~ 350 kJ

Spherical

*D. T. Michel et al., Rev. Sci. Instrum. 83, 10E530 (2012).

Substantial IFE technology development will be required after the demonstration of ignition

I2007

• Fusionresearchershavetoooftenmadeclaimsaboutenergyproduction that are not supported by demonstrated technology

• Anyenergydemonstrationmustbecosteffectiveandreliable

• Thepathtoaprototypepowerplantdemonstrationislongerandslowerthan most fusion researchers would like

• Anaggressivetechnologyprogramisrequiredafterthedemonstrationof ignition

The community must not “over-promise.”

I2064

LLE is making progress toward demonstrating ignition hydro-equivalentperformanceonOMEGA.

Summary/Conclusions

Significant progress toward demonstrating direct-drive ignition on the NIF is being made

• Polardrive(PD) will allow for direct-drive–ignition experiments at the National Ignition Facility (NIF) in the x-ray-drive configuration

• OMEGAdirect-drivecryogenictargetimplosionsaredefiningtheignitiondesign space

• Performancecontinuestoimprove

– the yield and ion temperature increase with implosion velocity up to 3.8 × 107 cm/s (maximum to date)

– the measured areal density agrees with 1-D predictions for adiabats >2.5

– Px increased to ~3.0 atm-s

– a NIF-scaled experimental ignition threshold factor has increased to ~0.15

• Progresstowarddevelopingpolardriveisongoing,includinginitialNIF PD experiments