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IAEA Chengdu , Oct 2006

Studies of isochoric heating by electrons and protons. IAEA Chengdu , Oct 2006. Andrew MacKinnon. Plus. Rapport: Papers IF/1 -R2b and 1F/1 - R2c.

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IAEA Chengdu , Oct 2006

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  1. Studies of isochoric heating by electrons and protons IAEA Chengdu , Oct 2006 Andrew MacKinnon Plus Rapport: Papers IF/1 -R2b and 1F/1 - R2c 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.

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

  4. Success in fast ignition requires a very large flux of MeV particles to be deposited in 10-20ps • FI (1,2) requirements: heat 300 g/cc, (R~2.5 g/cm2) with 18-20 kJ particles at MeV energy in 10 ps over 30-40 m dia. Cone • Electron Fast Ignition1 • Cone protects ignitor pulse from coronal plasma • Laser conversion to fast electrons ~ 30% • ~ 60 kJ laser energy required • Electron transport most important issue • DT fuel at 300g/cc • 40 m ignition spot Laser Coronal Plasma MeV electrons Curved proton rich target • Proton Fast Ignition2 • Currentlylaser conversion into protons ~10% • ~180 kJ laser energy required • Improving proton conversion efficiency most important issue MeV protons Laser Laser (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) • DT fuel at 300g/cc • 35 m ignition spot PW laser

  5. 30% coupling 15% coupling There is wide-ranging research in high intensity physics related to Fast Ignition in institutions around the world Results from Institute for Laser Engineering, Osaka have shown promise of cone focused scheme Kodama,et.al,Nature 412(2001)798 and 418(2002)933. “Cone” implosions Implosion beams 300 TW laser • 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

  6. Cone wire targets are being used to study electron transport at FI relevant laser intensities Target 10mCu wire /Al cone • 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 256 XUV 1 mm Laser 500 J, 0.8 ps 1mm RAL PW laser Vulcan 500 µm Cu Ka 1mm 10 mm * A.R.Bell et al., Cont Plasma 1997

  7. Proton FI: Proton conversion efficiency optimized by reducing target thickness and increasing hydrogen fraction on surface Electrons 0.1m CH4 layer Refluxing hot e 5m Al substrate H+ Fraction of Injected Energy Hot e C+6 Thermal e Al+4 • 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 Efficiency simulations for hydrides Cryogenic H2 Current experiments with contaminant layers • Experiments planned for mid FY07

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

  10. 68eV XUV Mesh image and XUV emission from the proton heated mesh indicates very small proton spot (~30-50m) Laser • 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 Proton dose (20MeV) 30m 30m

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

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

  13. Rapport: Papers IF/1 -R2b and 1F/1 - R2c • 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”

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

  15. Cones appear to strongly collimate MeV electrons into beams

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

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

  18. IF/1-2Rc Relativistic Electron Generation and Its Behaviors Relevant to Fast Ignition K. A. Tanaka1,2, H. Habara1,2, R. Kodama1,2, K. Kondo1,2, G.R. Kumar1,2,3, A.L. Lei1,2, K. Mima1, K. Nagai1, T. Norimatsu1, Y. Sentoku4, T. Tanimoto1,2, and T. Yabuuchi1,2 1Institute of Laser Engineering, Osaka University, 2-6 Yamada-Oka, Suita, Osaka 565-0871 Japan 2Graduate School of Engineering, Osaka University, 2-1 Yamada-Oka, Suita, Osaka 565-0871 Japan 3Tata 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.

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

  20. 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

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

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

  23. PIC simulation shows surface hot electrons at 1019 W/cm2

  24. Summary I • 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).

  25. 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

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