High-Performance Cryogenic Designs for OMEGA and the NIF

V. N. GoncharovUniversity of RochesterLaboratory for Laser Energetics

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58th Annual Meeting of theAmerican Physical SocietyDivision of Plasma Physics

San Jose, CA31 October–4 November 2016

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Ignition hydroequivalentOMEGA design, Rb/Rt = 0.75 (R75)

ASTER simulationOMEGA R75

SDD NIF R75 designEL = 1.6 MJ

Po

wer

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DTvapor

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8-nm CD

70-nm DT ice

EL = 26 kJ

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TC13024

Summary

Reducing cross-beam energy transfer (CBET) losses improves stability properties of ignition spherical direct-drive (SDD) designs at the National Ignition Facility (NIF)

• Hot-spot energy in direct-drive (DD) implosions is a factor of 5 or more larger than that of indirect-drive (ID) implosions

– the required hot-spot pressure in an igniting NIF-scale DD design must exceed 120 Gbar (350 Gbar in ID)

• Without CBET mitigation, SDD designs on the NIF have in-flight aspect ratios in excess of 30

– CBET mitigation in hydroequivalent designs on OMEGA involves reducing beam size relative to the target size* to Rb/Rt = 0.75

– high-yield and ignition SDD designs on the NIF require both beam-size reduction and wavelength detuning**

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* I. V. Igumenshchev, Phys. Plasmas 17, 122708 (2010); I. V. Igumenshchev, CI3.00002, this conference (invited). ** J. A. Marozas et al., NO5.00009 and P. B. Radha et al., NO5.00005, this conference.

Collaborators

T. J. B. Collins, J. A. Marozas, S. P. Regan, P. B. Radha, E. M. Campbell, D. H. Froula, I. V. Igumenshchev,

R. L. McCrory, J. F. Myatt, T. C. Sangster, and A. ShvydkyUniversity of Rochester

Laboratory for Laser Energetics

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TC12311e

The hot-spot pressure in an ignition design must exceed a threshold value

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Direct-drive designs are in a less-challenging hydrodynamic regime with CR K 22 and Phs > 120 Gbar; indirect-drive–ignition targets require CR = 30 to 40 and Phs > 350 Gbar.

~ /P E1th hs

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Pth

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60Hot-spot energy Ehs (kJ)

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Current high-foot indirect driveRequired: Phs = 350 to 400 GbarAchieved: Phs = 230 Gbar

Energy-scaled current OMEGA (Ehs = 0.44 kJ)Required: 140 GbarAchieved:* 56!7 Gbar

Mitigated CBET

IFAR: in-flight aspect ratio * S. P. Regan et al., Phys. Rev. Lett. 117, 025001 (2016).

• Pressure threshold for ignition

• For direct drive

~ ~ IFARP V P P/ //hs imp a a

1 3 5 30 1 3 a

TC12872a

Coupling losses caused by CBET are larger on the NIF-scale targets because of longer density scale length

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Laser intensity (#1014 W/cm2)

no CBET

with CBET

NIF

OMEGAA

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Pa

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ar)

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Phs ~ PaIFAR5/3

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Direct-drivedesigns

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TC13056

CBET losses make ignition target designs too unstable during acceleration

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NIF SDD designsVimp = 3.8 × 107 cm/sFull CBET, Pa = 90 Mbar

Current stability thresholdfor OMEGA cryogenic implosions

1-D LILAC simulations

Gain = 1Ya

Yno a

a = 4.1Phs = 72 GbarCR = 18.5

a = 2.9Phs = 90 GbarCR = 19 a = 1.4

Phs = 130 GbarCR = 21

CR: convergence ratio

Beam 1

Beam 2

CBET

TargetTarget

Beam 1

Beam 2

CBET

R bR b

RtRt

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Target diameter (nm)

CBETreduction**

Hyd

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Increase in density scale length

TC13057

CBET reduction* and improved laser coupling have been demonstrated on OMEGA by reducing Rbeam/Rtarget

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** V. N. Goncharov et al., J. Phys. Conf. Ser. 717, 012008 (2016); S. P. Regan et al., presented at the 57th Annual Meeting of the APS Division of Plasma Physics, Savannah, GA, 16–20 November 2015 (CI3.00005) (invited).

KE: kinetic energy * I. V. Igumenshchev, Phys. Plasmas 17, 122708 (2010); D. H. Froula et al., Phys. Rev. Lett. 108, 125003 (2012).

The performance of larger shells is limited by drive asymmetries. The near-term goal is to quantify and reduce laser power imbalance (part of the “100-Gbar” campaign).

Combination of Rb/Rt < 1 and wavelength detuning leads to robust high-yield SDD designs on the NIF

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Rb = Rt

Rb = 0.75 Rt

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IFAR

R75 with wavelength separation (Dm = !6 Å) Gain = 5; SDD NIF design

Yie

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DTvapor

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24-nm CD

200-nm DT ice

Initial experiments on the NIF with Dm = !2.3 Å confirmed predicted CBET reduction.*

*J. A. Marozas et al., NO5.00009, this conference.

201

510

50100

Ya Ya

Rb = Rt

Rb = Rt

Rb = 0.75 Rt

Rb = 0.75 Rt

Yno a

Yno a

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IFAR

R75 with wavelength separation (Dm = !6 Å)

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IFAR

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Ad

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at

Combination of Rb/Rt < 1 and wavelength detuning leads to robust high-yield SDD designs on the NIF

TC13058

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The effect of improved laser coupling on target performance will be tested using an R75 design on OMEGA with improved power balance

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• The effect of CBET is smaller on OMEGA because of shorter scale lengths

• Ignition hydroequivalent OMEGA design Rb/Rt = 0.75, IFAR = 21.8, a = 3Vimp = 3.7 × 107 cm/s

3-D ASTER* simulationsat peak neutron production

Current OMEGAnonuniformitiesPhs = 70 Gbar

“100 Gbar” illuminationuniformity and offsetPhs = 100 GbarP

ow

er (

TW

)

DTvapor

450 n

m

8-nm CD

70-nm DT ice

EL = 26 kJ

*I. V. Igumenshchev et al., Phys. Plasmas 23, 052702 (2016).

TC13024

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Summary/Conclusions

* I. V. Igumenshchev, Phys. Plasmas 17, 122708 (2010); I. V. Igumenshchev, CI3.00002, this conference (invited). ** J. A. Marozas et al., NO5.00009 and P. B. Radha et al., NO5.00005, this conference.

Reducing cross-beam energy transfer (CBET) losses improves stability properties of ignition spherical direct-drive (SDD) designs at the National Ignition Facility (NIF)

• Hot-spot energy in direct-drive (DD) implosions is a factor of 5 or more larger than that of indirect-drive (ID) implosions

– the required hot-spot pressure in an igniting NIF-scale DD design must exceed 120 Gbar (350 Gbar in ID)

• Without CBET mitigation, SDD designs on the NIF have in-flight aspect ratios in excess of 30

– CBET mitigation in hydroequivalent designs on OMEGA involves reducing beam size relative to the target size* to Rb/Rt = 0.75

– high-yield and ignition SDD designs on the NIF require both beam-size reduction and wavelength detuning**