1. IAEA Chengdu, Oct 2006 Andrew MacKinnon This work was performed under the auspices of the U.S. Department of Energy by University of California Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48. Studies of isochoric heating by electrons and protons Rapport: Papers IF/1 -R2b and 1F/1 - R2c Plus

2. Co -authors and acknowledgements K. Akli, F. Beg, M.H. Chen, H-K Chung, M Foord, K. Fournier, R.R. Freeman, J. S. Green, P. Gu, J. Gregori, H. Habara, S.P. Hatchett, D. Hey, J.M. Hill J.A. King, M.H. Key, R. Kodama, J.A. Koch, M Koenig, S. Le Pape, K. Lancaster, B.F.Lasinski, B. Langdon, S.J. Moon, C.D. Murphy,, P.A. Norreys, N. Patel, P.K Patel, H_S.Park, J. Pasley, R.A. Snavely, R.B. Stephens, C Stoeckl, M Tabak, W. Theobold, K. Tanaka, R.P. Town, S.C. Wilks, T. Yabuuchi, B Zhang, This work is from a US Fusion Energy Program Concept Exploration and Advanced concept exploration collaboration between LLNL, General Atomics, UC Davis, Ohio State, UCSD and LLE International collaborations at RAL,LULI and ILE have enabled most of the experiments Synergy within LLNL, through ‘Short Pulse’ S&T Initiative has helped the work US collaboration in FI has recently expanded in a new Fusion Science Centre linking 6 Universities and GA with LLNL and LLE and a new Advanced Concept Exploration project between LLNL,LLE,GA, UC Davis, Ohio State and UCSD

3. Fast Ignition entails assembly of compressed fuel followed by fast heating by MeV particles Ignition driver: short pulse laser Compression driver: Laser Step 1. Compress fuel critical surface Step 2. Ignite fuel Initial concept utilized kJ source of MeV electrons in picosecond pulse to ignite imploded capsule ( M. Tabak et al., Phys Plasmas 1, 1626, 1994) MeV particles

4. Success in fast ignition requires a very large flux of MeV particles to be deposited in 10-20ps Electron Fast Ignition 1  Cone protects ignitor pulse from coronal plasma  Laser conversion to fast electrons ~ 30%  ~ 60 kJ laser energy required  Electron transport most important issue Proton Fast Ignition 2  Currently laser conversion into protons ~10%  ~180 kJ laser energy required  Improving proton conversion efficiency most important issue (1) Atzeni et al.,PoP (1999) (2) Roth et al.,86,436 PRL 2000, Atzeni et al., 2002; Temporal et al., PoP 9,3102 (2002) FI (1,2) requirements: heat 300 g/cc, (  R~2.5 g/cm 2 ) with 18-20 kJ particles at MeV energy in 10 ps over 30-40  m dia. PW laser Laser DT fuel at 300g/cc 35  m ignition spot Coronal Plasma Cone DT fuel at 300g/cc 40  m ignition spot MeV electrons MeV protons Laser Curved proton rich target

5. There is wide-ranging research in high intensity physics related to Fast Ignition in institutions around the world 15% coupling 30% coupling Kodama,et.al,Nature 412(2001)798 and 418(2002)933. Results from Institute for Laser Engineering, Osaka have shown promise of cone focused scheme Existing experimental Facilities: United Kingdom,France, LLNL(Titan), SNL, Universities,… Theory: US, UK, France, Germany, Italy, Japan, China, India Upcoming Facilities: Omega EP(Rochester), NIF ARC(LLNL), FIREX I(Japan) Proposed facilities : HIPER(Europe), FIREX II(Japan), China Implosion beams 300 TW laser “Cone” implosions

6. Cone wire targets are being used to study electron transport at FI relevant laser intensities 1  m 10  m 256 XUV Cone/Wire represents conductivity channel in FI scheme: test-bed for existing electron transport models K  emission images show 100  m exponential scalength Bell 1D analytic model* gives similar scale-length to experiment Peak temperature measured by XUV imaging to be 350 eV with 100  m scale length ~ 1.2% of laser energy 1D numerical model injecting 1.2% of laser energy as hot electrons matches observed K  1D transport scaling gives 20% coupling at 40  m diameter - This would be viable for FI * A.R.Bell et al., Cont Plasma 1997 Target 10  mCu wire /Al cone 500 µm Cu K  1 mm RAL PW laser Vulcan Laser 500 J, 0.8 ps

7. Al+4 Hot e C+6 Thermal e H+ Fraction of Injected Energy Refluxing hot e 5  m Al substrate 0.1  m CH 4 layer Electrons Proton FI: Proton conversion efficiency optimized by reducing target thickness and increasing hydrogen fraction on surface  Refluxing hot electrons continuously lose energy to thermal ions and electrons in substrate  Contaminant layer containing hydrogen ionized & accelerated by MeV/  m electric field  Reducing target thickness increase conversion efficiency as hot electron pressure increases  Increasing proportion of H + in layer increases conversion eff -> hydrides or pure H2 should provide highest conversion efficiency

8. Varying Z of hydride layer could yield factor 2-3 enhancement in proton conversion efficiency Current experiments with contaminant layers Cryogenic H2 Experiments planned for mid FY07 Efficiency simulations for hydrides

9. Shot No:060622_s1: 20µm thick, 350µm Diameter Al hemi-shell with 25µmx25µm Cu mesh at 1mm spacing RCF pack for measuring proton dose This technique allows simultaneous determination of location of proton focus, size of proton spot and extent of heated region Proton focusing: Mesh imaging of the proton beam provides great deal of information on focusing mechanism Fine mesh w/ element separation = 25  m Laser : spot~50µm 1mm Focal Plane 70mm x Equatorial Plane d Oblique view XUV Imagers at 68 and 256eV to measure size of heated region Side view d = 250  m Laser view mesh Laser View of xuv

10. Mesh image and XUV emission from the proton heated mesh indicates very small proton spot (~30-50  m) 68eV image shows very bright image and large plume - consistent with high Temp 256 eV image also shows ~30-50  m heated region RCF shows 3-4 mesh elements in 20MeVproton beam - agrees well with 256eV image Data is being used to test proton focusing models 256eV XUV Laser 30  m Proton dose (20MeV) 68eV XUV 30  m

11. User experiments will begin in 2008 Integrated experiments are being planned for Omega EP: These will test fast ignition concepts at kJ short pulse energy levels

12. 2 x1.2 kJ per beam line One beam line in FY09 (Option for 13 kJ quad) Fast ignition experiments can also be carried out on the NIF using the high energy radiography beams

14. Paper IF/1 -2b: R. Kodama et al., “ Plasma photonic devices for Fast Ignition Concept in Laser Fusion Research” Paper 1F/1 - 2c: K. Tanaka et al., “Relativistic Electron Generation and its behaviors Relevant to Fast Ignition” Rapport: Papers IF/1 -R2b and 1F/1 - R2c

15. Paper IF/1 -2b: Describes how cones and other guiding devices modify Electron generation in FI

16. Cones appear to strongly collimate MeV electrons into beams

17. Integrated experiments show plasma heating by short pulse, consistent with collimated electron beams

18. Please see poster IF/1-2Rb for full paper

19. Relativistic Electron Generation and Its Behaviors Relevant to Fast Ignition K. A. Tanaka 1,2, H. Habara 1,2, R. Kodama 1,2, K. Kondo 1,2, G.R. Kumar 1,2,3, A.L. Lei 1,2, K. Mima 1, K. Nagai 1, T. Norimatsu 1, Y. Sentoku 4, T. Tanimoto 1,2, and T. Yabuuchi 1,2 1 Institute of Laser Engineering, Osaka University, 2-6 Yamada-Oka, Suita, Osaka 565-0871 Japan 2 Graduate School of Engineering, Osaka University, 2-1 Yamada-Oka, Suita, Osaka 565-0871 Japan 3 Tata Institute of Fundamental Research, Homi Bahbha Rd., Mumbai 400 004 India 4 Department of Physics, University of Nevada, Reno, Nevada 89521-0042 U.S.A. IF/1-2Rc

20. To increase the heating efficiency of the core plasma, we propose a foam cone-in-shell target design. Target design improvement: foam cone-in-shell target for increasing the heating efficiency of core plasma Multiple implosion beams Relativistic laser Gold cone with inner tip covering with a foam layer Fuel shell

21. Au foam coating enhances laser absorption and hot electron generation Hot -e yield measurement via the back x-ray emission from the target rear due to the heating from hot –e beams -weak front x-ray emission from the Au foam- coated target. This is due to the low density of the foam. -stronger back x-ray emission from the Au foam coated target. This is attributed to higher laser absorption and more hot electrons generated with the foam coated target. Back x-ray emission is caused by the hot –e beam heating of the target rear. -target is thick so that the front x-ray emission may not be responsible for the enhancement of back x-ray emission with foam coated target. Moreover, if it happens, one would expect weak x-ray emission from the foam coated target rear, contrary to the experimental results. -narrow band-width x-ray image diagnostics needed to give the relative hot –e yield through assuming Plankian emission from the target rear. -quantitative models and simulations needed

22. Surface Acceleration of Fast Electrons with Relativistic Self-Focusing in Preformed Plasma

23. Hot electron distribution differs for with and without plasmas.

24. PIC simulation shows surface hot electrons at 10 19 W/cm 2

25. We propose a foam cone-in-shell target design aiming at improving the cone-in-shell target design to increase the laser energy deposition in the dense core plasma. Our element experiment results demonstrated increased laser energy coupling efficiency into hot electrons without increasing the electron temperature and beam divergence with foam coated targets in comparison with solid targets. This may enhance the laser energy deposition in the compressed fuel. Phys. Rev. Lett., A.L.Lei, K.A. Tanaka et al., 96, 255006(2006). Summary I

26. Summary II Surface direction hot electrons observed at oblique incidence UIL experiment. Relativistic laser self-focusing increases laser intensity causing surface hot electrons. Several tens of MGauss field inferred H. Habara, K.A. Tanaka et al., Phys. Rev. Lett. 97, 095004(2006). Please see poster IF/1- 2Rc for more details