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FSC Overview of shock ignition Shock Ignition Workshop March 8-10, 2011 Rochester, NY R. Betti Fusion Science Center Laboratory for Laser Energetics

Overview of shock ignition

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Page 1: Overview of shock ignition

FSC

Overview of shock ignition

Shock Ignition WorkshopMarch 8-10, 2011Rochester, NY

R. BettiFusion Science CenterLaboratory for Laser Energetics

Page 2: Overview of shock ignition

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K. Anderson (LLE)R. Nora (LLE)C. Stoeckl (LLE)W. Theobald (LLE)J. Bates (NRL)A. Schmitt (NRL)M. Lafon (CELIA)X. Ribeyre (CELIA)G. Schurtz (CELIA)S. Weber (CELIA)V. Tykhonchuk (CELIA)S. Atzeni (U. Rome)J. Perkins (LLNL)O. Klimo (CTU)and others……

I will show results from:

Page 3: Overview of shock ignition

FSCOutline

• The physics of shock ignition

• Target optimization

• 1D gain curves

• 2D simulations

• Experimental results

Page 4: Overview of shock ignition

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• Thick shells (with large fuel mass) produce high gains if ignited

• Thick shells have good hydro-stability properties (because they are thick)

• For a fixed laser energy, thick shells have low implosion velocity

• Low implosion velocity leads to low hot spot pressure (P~Vi2-3)

• Low pressure hot spots do no ignite (Pτ> 30 Gbar/ns)

• The energy required for ignition scales as E~ 1/P2-2.5

How do we ignite low-velocity implosions?

The puzzle of high gains: how to ignitelow-velocity imploding targets

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Page 6: Overview of shock ignition

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Two different mechanisms related to rarefactionwave propagation limit the hot spot pressure

R. Nora and R. Betti, submitted to Phys. Plasmas

Page 7: Overview of shock ignition

Without rarefaction waves, the peak hot spotpressure would be twice as high

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Withoutrarefaction

Withrarefaction

R. Nora and R. Betti, submitted to Phys. Plasmas

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Late shocks can suppress rarefaction waves.There are three ways shocks can be launched.

No-rarefactiontechnique(requires manyhighly-synchronized“weak” shocks)

No-transmissiontechnique(requires onemoderate shock)

Re-shocktechnique(requires onestrong shock)

R. Nora and R. Betti, submitted to Phys. Plasmas

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The enhancement in hot spot pressure variesfor different techniques (total energy is kept constant)

No-rarefactiontechnique with two“weak” shocks

In principle,using ∞ shocks

No-transmissiontechnique with one shock

Re-shock technique with one shock (for a given shock strength)

R. Nora and R. Betti, submitted to Phys. Plasmas

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The re-shock technique produces the highest hot spot pressure

Shock pressurein Gbar

The shock pressureis high because ofthe planar geometry

R. Nora and R. Betti, submitted to Phys. Plasmas

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In spherical geometry, convergence effects amplifythe ignitor shock by about ten fold

V1

V2

0.5 0.6 0.7 0.8 0.9 10

100000

200000

300000

400000

500000

600000

Cent

ral P

(Mba

r)

Time (ns)

V1

V2

0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.50

100000

200000

300000

400000

Cent

ral P

(Mba

r)

R

RH

O

P

0 50 100 1500

20

40

60

80

100

120

010002000300040005000600070008000900010000110001200013000140001500016000

P(M

bar)

R

RH

O

P

0 50 100 1500

50

100

150

200

0

10000

20000

30000

40000

P(M

bar)

P

ρ

P=7Gbar

P=20Gbar

P

ρ

500Mbar Shock

2Gbar Shock

no shock

w shock

w shock

no shock

~2 pressureenhancement

~3 pressureenhancement

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LILAC agrees with the predictions of the simplemodel for both shock amplification and pressureenhancement

300-400Mb Shock

Page 13: Overview of shock ignition

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Optimal SI targets are wetted-foam shells(in the absence of hot electron pre-heat)

Page 14: Overview of shock ignition

SI wetted-foam target have low IFARsand good stability properties

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Page 15: Overview of shock ignition

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Page 16: Overview of shock ignition

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Shock-ignition targets with CH ablators have higherIFARs. Hydrodynamic instabilities can be a concern.

K. Anderson (this workshop)

Page 17: Overview of shock ignition

Also see K. Anderson (this workshop)

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Gain curves for shock ignition look impressive but need to assess the sensitivity to preheat (during the main pulse) and (for CH targets) to laser imprinting.

JL Perkins (LLNL) A. Schmitt (NRL)

Page 19: Overview of shock ignition

3-fold pressure amplifications are found for HiPER targets.Gains curves are derived by hydro-equivalent scaling

Lafon, Ribeyre, Schurtz, Phys. Plasmas 17, 052704 (2010)

Page 20: Overview of shock ignition

Ribeyre, Schurtz, Lafon, Galera, Weber, PPCF 51, 015013 (2009)

The spike power and launching time are optimizedfor HiPER shock ignition targets

HiPER shock ignition target

Page 21: Overview of shock ignition

Bates, Schmitt, Fyfe, Obenschain, Zalesak, High Energy Den Phys 6, 128 (2010)

Comprehensive 2D simulations of SI KrF targets, withzooming are carried out by the NRL group

GAIN=103EL = 398kJ

Page 22: Overview of shock ignition

Ignitor-return shock collision seems to reduce thedeceleration RTI growth before ignition

Atzeni, Davies, Hallo, Honrubia, Maire, Olazabal, Feugeas, Ribeyre,Schiavi, Schurtz, Breil, Nicolai, Nucl. Fusion 49, 055008 (2009)

Page 23: Overview of shock ignition

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1D PIC simulations at SI-spike relevant intensities showlow-temperature hot electrons with an energetic tail

Klimo, Weber, Tikhonchuk, Limpouch, Plasma Phys Cont Fus 52, 055013 (2010)

Page 24: Overview of shock ignition

. Thot~ 45keV

C. Stoeckl, APS 2009; W. Theobald et al, PPCF 51, 124052 (2009);

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Neutron yields:Compare SI and CHS targets,40 µm CH shells filled with25 atm D2 gas

Areal densities:Compare SI and CHS targetsVarying fill pressures

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Higher neutron yields and areal densities are measuredin shock ignition experiments using thick CH targets

W. Theobald et al, Phys Plasmas 15, 056306 (2008)

Page 26: Overview of shock ignition

Beam pointing schemes are being explored for Polar Drive Shock Ignition on the NIF

• Focusing separate shock beams at a smaller radius late in time allows better coupling of energy to the target.

• A scheme with split quads would allow best irradiation uniformity on target, but requires time-consuming “rewiring” of NIF seed pulses.

• Another scheme employing full quads, half for the main drive and half for the shock pulse was recently proposed* by Steve Craxton

*Craxton, et al., APS-DPP 2010

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• Need to demonstrate the generation of >300Mb shockwaves in long density scalelength plasmas

• Need to demonstrate that hot electrons (mostly from TPD)during the main pulse can be controlled

• Need to demonstrate that the hot electrons above 100keVduring the intensity spike do not preheat the capsule

• Need to demonstrate hot-spot integrity at the highconvergence ratios typical of shock ignition

Significant progress has been made in the past two years, but there are still important issues to be resolved for the validation of shock ignition

Conclusions