1. Review of Fast Ignition HEDLP Workshop Washington Michael H. Key Lawrence Livermore National Laboratory August 25 to 27, 2008 Work performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under Contract No. W-7405-ENG-48. UCRL-PRES-

2. K. Akli 2, F. Beg 5, R. Betti 6, D. S. Clark 1, S. N. Chen 5, R.R. Freeman 2,3 S Hansen 1,S.P. Hatchett 1, D. Hey 2, J.A. King 2, A. J. Kemp 1, B.F. Lasinski 1 B.Langdon 1,T. Ma 5, A.J. MacKinnon 1, D. Meyerhofer 10, P.K. Patel 1, J. Pasley 5 R.B. Stephens 4, C. Stoeckl 6, M. Foord 1, M. Tabak 1, W. Theobald 6, M. Storm 6 R.P.J. Town 1, S.C. Wilks 1, L. VanWoerkom 3, M.S. Wei 5, R. Weber 3, B. Zhang 2 1 Lawrence Livermore National Laboratory, Livermore, CA 94550, USA 2 Department of Applied Sciences, University of California Davis, CA 95616, USA 3 Ohio State University, Columbus Ohio, 43210 USA 4 General Atomics, San Diego, CA, 92186, USA 5 University of California, San Diego, San Diego, CA, 92186, USA 6 Laboratory of Laser Energetics, University of Rochester, NY, USA Special thanks for advice and information : Mike Dunne, Wolfgang Theobald, Javier Honrubia, Hiroshi Azechi, Riccardo Betti Acknowledgements

3. Outline Concept of FI Ignition requirements and gain Cone coupled electron FI Channel electron FI Proton and mid Z ion ignition Major integrated experiments Summary

4. Fast Ignition is ICF with separate compression and ignition drivers Laser hole boring and heating by laser generated electrons was the first FI concept 1MeV electron range matched to ignition hot spot Absorption of intense laser light produces forward directed electrons e-beam temperature = ponderomotive potential 100 kJ, 20 ps Hole boring for laser to penetrate close to dense fuel Pre-compressed fuel 300 gcm -3 M Tabak, S Wilks et al. Phys. Plasmas1,1626, (1994) Laser

5. 2D simulations of ignition and burn by 15kJ, 2MeV, 20µm, 15ps e-beam 00.511.522.5 50 100 150 200 Maximum FI gain at 300g/cc 100kJ PW 200kJ PW Several modeling studies have confirmed that FI offers high gain at low driver energy e.g. R. Betti, A.A. Solodov, J.A. Delettrez, C. Zhou, Phys. Plasmas 13, 100703 (2006) Driver Energy (MJ) Gain >100x gain with 500kJ driver is attractive for IFE

6. Laser Au cone The cone coupled FI concept provides a clear path for the laser with the electron source close to the ignition spot 100  m DT =2.2 g cm -2 Radiation - hydro simulations are well developed for ICF and allow hydro--design optimization for FI S Hatchett et al. - 30 th Anom. Abs. Conf. Maryland, May 2000

7. 15% coupling 30% coupling R Kodama et.al. Nature 412(2001)798 and 418(2002)933. Implosion beams 0.5 PW laser Gekko “Cone” implosion The first cone coupled fast ignition experiment at the Gekko laser in Japan gave very encouraging results 0.5PW ignitor beam gave ≈ 20% energy coupling to imploded CD 1000x increased DD neutrons Outstanding question for FI is What coupling is the efficiency at ignition scale ? 50  m SP Laser

8. The energy required in the ignition hot spot and the optimum electron energy are well established E   z 2r DT Fast Ignition region T = 12keV,  R = 0.6 g/cm 2 Optimal ignition criteria: E = 18kJ in electrons P = 0.9 PW => t = 20ps I = 6.8x10 19 W/cm 2 => r = 20  m For  = 300 g/cm 3 assembly we need to deliver to the fuel: S. Atzeni, Phys. Plas. 8, 3316 (1999) M Tabak et al Fus. Sci. Tech. (2006) Coupling efficiency depends on: – laser conversion to electrons – energy spectrum of electrons – collimation of electron transport – cone tip to dense plasma separation Maximizing coupling efficiency at full scale is the overall design challenge in FI

9. Hybrid PIC coupled to hydro-modeling predicts the electron transport and electron coupling efficiency to the ignition spot No B field 115 kJ With B field 43 kJ300kJ drive 1D fuel The focusing effect of azimuthal B from dB/dt= curl(E) increases transport efficiency by factor >2.5x A A Solodov et al. ( preprint of publication )

10. Increased source divergence and distance to fuel increase the ignition energy - reduction by B field collimation is robust Coupling of electron source to ignition hot spot can be > 50% efficient for typical beam divergence and transport distance J Honrubia and J Meyer ter Vehn EPS Plasma Conf 2008

11. Cold target experiments at <1PW show typically 40 o cone angle of electron transport Al thickness micron LULI 20J,0.5 ps RAL 100J,0.8 ps Cone angle 40 o Min radius 37  m 180  m Cu 20  m Al 20  m RAL data New warm plasma experiments are planned using long pulse beams to prepare plasma ( A Mackinnon talk to follow ) 40 o cone R Stephens et al. Phys Rev E,69, 066414, ( 2004)

12. Recent 2D PIC modeling predicts a cooler two temperature electron source and 30 to 35% conversion to electrons Chrisman, Sentoku and Kemp PoP, 2008

13. Cool component is from light pressure steepened interface and hot component from critical density shelf Possibility of optimizing T hot and absorption efficiency using low density foam layer to tailor the density profile H Sakagami et al. FIW 2008A Kemp et al. PRL 2008

14. Coupling efficiency and effective T hot inferred from Ohmic potential limited transport in cone- wire targets at Vulcan PW 500 µm 1  m 10  m 256 XUV M Key et al Proc IFSA 2005 and J King et al PoP ( submitted) Sensitivity to pre-pulse and cone wall thickness measured at Titan

15. Electron source studies with the Titan laser also point to eletron temperature < ponderomotive potential Hybrid PIC modeling of K  data gives conversion efficiency T hot analysis using focal spot power fraction v intensity Bremsstrahlung data consistent with CSK PIC modeling More in talk by R Stephens to follow

16. Point designs require simultaneous optimizing of many aspects of the hot electron generation, electron transport and hydrodynamics Compressed fuel Near 1-D isochoric implosions to minimize low density high temperature hotspot at center Cone Minimize transport distance from cone to fuel Minimize high-Z cone material in fuel Cone tip survival clear path for laser The cone tip hydro problem is very challenging at full scale because at fixed separation of tip and ignition spot the pressure is much higher relative to smaller scale e.g. Gekko experiment

17. 40  m 90  m 298  m 25 kJ Omega Scale 1D target designs for direct-drive FI use massive wetted foam shells insensitive to fluid instability  R  3g/cm 2  R  1.9g/cm 2  R  0.7g/cm 2  300-500g/cm 3 R. Betti and C. Zhou, Phys. Plasmas 12, 110702 (2005)

18. E L  20kJ P  25-34atm  1.3 V  210 7 cm/s Peak  R is 0.26g/cm, 2 the highest  R to date on OMEGA Empty shells would achieve  R  0.7g/cm 2 C. Zhou, W. Theobald, R. Betti, P.B. Radha, V. Smalyuk, C.K.Li et al, PRL2008 CH implosions with low adiabat were tested on OMEGA D 2 or D 3 He D- 3 He fusion proton energy loss measured the high  R

19. NIF can drive full scale FI targets using 650kJ indirect drive and ID designs for CD and DT are being developed Small hotspot  r ~ 2 g/cm 2 1235 µm 1070 µm 870 µm 1139 µm 1087 µm DT Be 10 -6 g/cm 3 DT Be density (g/cm 3 ) radiustime (ns) T rad (eV) Be (0.9%) Cu Peak power: 70TW Pulse length: 32 ns Max blue energy: 650kJ Contrast ratio: 35:1 Peak T rad = 210eV Hydro tests with Be/CD targets on NIF will begin in 2010 More in talk by D Clark to follow

20. Destruction of cone tip by hydro jet and entrainment of ablated high z cone in to fuel are important design issues Stoeckl C. et al., Phys. Plasmas 14 112702 (2007) Nagatomo et al PoP 2007 CH tamped cone

21. Direct ignition by the main PW pulse ( super-penetration ) is an option being considered thro’ modeling and experiment 1D hydro- modeling has established the density profile PIC modeling has shown the main pulse penetrating beyond critical density with relativistic self focusing Y Sentoku et al. Fus Sci Tech,49,278,(2006) Excessive T hot is a problem which could be mitigated with a shorter wavelength N c to >1 gcm -3 requires >200  m penetration -not modeled Shorter wavelength would allow penetration closer to the ignition region 1mm N c /4 NcNc 1gcm -3 There is however no self consistent point design for ignition

22. 2D PIC modeling has shown channel production up to critical density in a plasma of full FI scale. Lacks modeling to show channel extension by hole boring to bring the laser close enough to the ignition region (requires ~200  m hole boring to few gcm -3 ) The propagation of the main pulse in the channel has not been modeled Shorter wavelength makes channel to higher density The original channeling and hole boring scheme using a pre- pulse is being studied in the Omega EP project 10 19 Wcm -2 hole boring in 1 mm scale sub criticaL density plasma C Ren FIW (2006) There is so far no point design for high gain

23. Ion fast ignition by protons or carbon ions offers alternatives with some attractive features Light pressure and BOA for C ions NEW TNSA for protons J Honrubia EPS Plasma Conf 2008 M Key et al Fus Sci Tech 2006 J Fernandez et al. Proc IFSA 2007 and talk to follow

24. A conceptual design for proton fast ignition illustrates the issues XUV PW laser Laser Proton heating Cu K  image  m Laser 100kJ,3 ps 10 20 Wcm -2 50kJ electrons kT=3 MeV 20 kJ protons kT= 3 MeV Radially uniform proton plasma jet required for smallest focal spot Proton source foil protects rear surface from pre-pulse -thickness limits conv. efficiency Cone maintains vacuum region for proton plasma jet formation and protects surface of proton source foil DT fuel at 500g/cc 60  m ignition spot (same as electron ignition) Scattering limits thickness of cone tip and separation from fuel Requirements based on Ignition with protons : Atzeni et al.Nucl Fus 42,(2002)

25. Modeling of focusing suggests that FI requirements can be met with open geometry ( cone enclosed study ongoing ) Hybrid PIC modeling by M Foord LLNL using LSP code 80% of energy at >3MeV can be delivered to 60  m focal spot from an f/1 segment of a 300  m radius spherical shell 10  m Au,1  m H, T hot 3 MeV, 47% conversion to protons >3MeV

26. Good electron to proton conversion efficiency with no depletion are predicted for thin Au targets with a hydride layer Electron to Proton eff. H 35% ErH 3 30% Hybrid PIC modeling by M Foord LLNL using LSP code More in talk by M Foord to follow

27. Definitive integrated Fast Ignition experiments will be performed with facilities soon to come on line Omega EP PETAL LIL FIREX INIF ARC Quad NIF FI high gain HIPER Firex II Schedule d Fall 20082009-2010 2011??? Long pulse(kJ) 256010800 20050 Short pulse(kJ) 2.6 / beam 5.2 max 3.510 60 1w?100 2w?50 Scaled hydro  R 0.2?0.1522 to 3 Density g/cc 300?150300-500 Hole boring Y?Y? Cone guided YYYYYYY Near ignition 5keVY High gain>100 More in talks by W Theobald and A MacKinnon to follow

28. The high gain and low driver energy and possibility of two opposed narrow cones of laser beams are attractive for IFE Pure fusion and also fusion fission hybrids burning nuclear waste, are possible I-LIFT (Japan), Hiper (Europe), LIFE (LLNL ) are examples of study of FI power plant concepts

29. HED Science and IFE relevance of Fast Ignition ( FI ) Fast ignition requires extremely high energy density 10keV, 300 to 500 g/cc in (40  m) 3 FI uses ignition methods (laser generated electron and ion beams) that can heat any material isochorically (using inertial confinement) to multi- keV temperature. Thermonuclear burn creates still higher energy density FI cone targets will allow HED science using precise exposure of matter to extreme energy density and radiation and particle fluxes The underlying science of FI is that of more general HED science FI is an outstanding example of an application of HED science FI has significant advantages for an IFE power plant ( lower driver energy,higher gain, better laser beam geometry ) The potential and prospects of FI have led to major investments worldwide

30. Scientific challenges and opportunities Validated modeling and control of the source characteristics of laser generated relativistic electrons ( =, >30% conversion ) at FI relevant laser parameters ( >10 20 Wcm -2, ~100kJ, <20 ps ) Validated modeling and control of transport of electron energy to ignition spot - (magnetic collimation > 50% electron coupling efficiency ) Advanced hydrodynamic design meeting multiple constraints for FI point designs e.g. optimizing implosion around a cone tip - designing targets for IFE with laser beams restricted to two cones Developing >10% efficient ion acceleration concepts to meet FI requirements ( e.g TNSA, light pressure and BOA concepts ) Validated modeling and control of the focusing of laser generated ion beams to meet FI requirements ( 40 micron focal spot ) Novel HED science using thermonuclear burn

31. Anticipated technical advances and opportunities Better integrated codes ( PIC, hybrid PIC, rad-hydro)- benchmarked by experiments - improved target point designs Next generation large scale integrated experiments using point designs ( Omega EP, FirexI, Petal and NIF ARC Quad ) High gain FI using adapted or new laser facilities (adapted NIF or LMJ, Firex II, Hiper ) HED science applications of FI thermonuclear burn IFE power plant concepts ( pure fusion and hybrid fission fusion ) Laser technology for rep rated FI Low cost high volume target fabrication and injection IFE demo and IFE power production