Direct Heating and Basic Experiments for Fast Ignition

Transcription

1 Direct Heating and Basic Experiments for Fast Ignition ILE Osaka K. A. Tanaka*, R. Kodama, Y. Kitagawa, Z. Chen, K. Kondo, R.G. Kumar, T. Jitsuno, T. Johzaki, An le Lei, T. Matsuoka, K. Mima, N. Miyanaga, K. Nagai, T. Norimatsu, H. Nagatomo, M. Tanpo, T. Yabu-uchi, J. Zheng** and Y. Izawa Institute of Laser Engineering Osaka University Presented at IAEA meeting, 2004

2 Comparative study of electron and proton isochoric heating for fast ignition 20th IAEA Fusion Energy Conference Vilamoura, Portugal 1 to 6 Nov Michael H. Key F. Amiranoff, C. Andersen, D. Batani, S.D. Baton, T. Cowan, N. Fisch, R. Freeman, L.Gremillet T. Hall, S. Hatchett, J. Hill, J. King, R. Kodama, J. Koch, M. Koenig, B. Lasinski, B. Langdon A. MacKinnon, E. Martinolli, P. Norreys, P. Parks, P Patel, E.Perelli-Cippo,D Price, M. Rabec Le Gloahec, M. Rosenbluth, C. Rousseaux, J.J. Santos, F. Scianitti, R. Snavely, R. Stephens M. Tabak, K. Tanaka, R. Town 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.

3 Fast ignition has new potential for IFE - we report experimental results from Japan and the USA Coned guided ignition Super penetration ignition Electron transport and heating Proton focusing and heating

4 Outline Japan (LLE) Study of the super-penetration mechanism for fast ignition -super penetration penetration in preformed plasma -super penetration in an implosion US Electron transport and isochoric heating US Proton focusing and isochoric heating Future prospects in the US and Japan

5 Introduction Original idea using ultra-intense laser penetration is studied into over-dense plasmas. We could observe the laser light penetration into those plasmas at Laser intensities higher than W/cm 2 with TW lasers. Direct heating was tested onto a highly compressed core with a large Spherical corona plasma with our PW laser. The result shows that there is a factor 4 increase in DD neutrons Compared to an only implosion shot. ILE Osaka

6 Super-penetration of PW Laser into Thick Overcritical Dense Pre-plasma PW: E=150 J I=5x10 18 W/cm 2 GXII#2: E=44 J I=1.7x10 13 W/cm 2 ILE Osaka Diagnostics: 1 XPHC image 2 XUV image 3 ESM 4 Optical imaging 5 ILESTA Hydro dynamic code Experimental setup

7 X-ray pinhole camera image indicates 0.3PW whole-beam relativistic self-focused laser penetration into thick overcritical dense pre-plasma PW: E=150 J I=5x10 18 W/cm 2 ILE Osaka GXII#2: E=44 J I=1.7x10 13 W/cm 2 Preplasma: peak density=10n c thickness= 80 Ãm The relativistic laser whole-beam self-focuses in the underdense plasma and then super-penetrates into the overdense region, retaining a narrow beam diameter. The plasma channel cross section is 25 µm in diameter(fwhm).

8 Hot electron spectra exhibit close correlation to the PW laser focus positions ILE Osaka Hot electron temperatures: 3.1MeV at focus point 0.6n c 1.8 and 2.5MeV at 0.9n c When the PW laser focus point is set at 0.9 n c, the spectrum shows 2 Maxwellian temperatures. The values of temperature are very close to the early PIC simualtion results by Pukhov et al in the cases of underdense and overdense plasmas at close laser intensities, indicating laser penetration into overdense plasma.

9 Experimental setup for PW laser illumination of pre- imploded CD shell 12 green beams implode with 2.4 kj in 1.2 ns GXII PW backscatter 180J/0.7ps a=3 XSRC IP KDP LENS RPP IP IP ILE Osaka Target: Deuterated polystyrene (CD) shell of 500 µm in diameter and 7 µm in thickness, no gas filled. PW IP IP Collimater 3m Neutron scintillator Mandala X-ray IP Streak Spectrometer 13.55m Mandala

10 Thermal neutrons vs PW timing with ratio of Beam fusion/thermal yield Thermal: neutrons at /-0.2 MeV Beam fusion: from 1.5 MeV to 3.5 MeV Neutrons/4π sr Thermal neutrons Implosion phase Beam Thermal beam/thermal ratio 8 expansion stagnation Beam/thermal neutron yield Flow of shell radius (full size 60 µm) PW timing [ps]

11 Conclusion 1. We investigate the laser propagation in plasmas at the highest powers ever attempted. The pre- plasmas generated have long overdense region thickness and high peak plasma density. 2. Our X-ray images provide direct proof of laser channeling extending from the underdense to the overdense plasmas. 3. We find that the transmittance values of laser light are strongly dependent on its focus positions and hot electron spectra show close correlation to the laser focus positions. ILE Osaka 4. We find the suitable PW laser focus positions for the laser superpenetration into the overdense plasmas. This result is very important for future multi-pw laser aiming at Fast Ignition study.

12 Outline Japan (LLE) Study of the super-penetration mechanism for fast ignition -super-penetration penetration in preformed plasma -super-penetration in an implosion US Electron transport and isochoric heating US Proton focusing and isochoric heating Future prospects in the US and Japan

13 XUV and Kα images give good insight into electron transport and isochoric heating Electron flux density Front plasma plume 500 µm Rear surface heating Cu Kα image XUV image _XUV_s4 500x500x25 µm Cu foil,77j, 14 ps, 1.8x10 18 Wcm -2

14 K α image data show 40 o transport cone angle for deep penetration in Al RAL 100J,0.8 ps 180 µm Spot diameter, µm LULI 20J,0.5 ps RAL data Cone angle 40 o Min radius 37 µm xray Al thickness, µm Al thickness micron Al 20 µm Cu 20µm R Stephens et al. Phys Rev E,69, , ( 2004)

15 Comparison of isochoric heating data with a hybrid PIC model ( LSP ) shows agreement using heuristic injected electrons M H Key et al. Proc IFSA Conf 2003 Hybrid PIC simulation ( LSP) of electron transport through 100 µm of Al for conditions of experiment with the RAL 100 TW laser. Needs ab initio model for electron source

16 Kα imaging enables study of energy flow via cone targets into FI surrogates - slabs,wires etc Cu wire Au cone Cu coated Au cone 500 µm Cu doped Al slab 950 µm We are investigating model predictions of enhanced laser and electron energy flux from cones

17 Kα from six beam implosion of Cu doped CD shell at RAL Vulcan shows 20% conversion to electrons thro core Exploding 20% energy via core Core heating depends on classical v anomalous stopping?

18 Outline Japan (LLE) Study of the superpenetration mechanism for fast ignition -super penetration penetration in preformed plasma -super penetration in an implosion US Electron transport and isochoric heating US Proton focusing and isochoric heating Future prospects

19 Focused proton isochoric heating can give higher temperature than electron isochoric heating- expts at RAL PW laser 1000 Temperature ev RAL PW data Al thickness micron

20 Optimum focal plane for focused proton heating determined at the Gekko PW laser Divergence from planar target mapped onto sphere predicts best focus Data from 250J,1ps pulses at Gekko The best focus and peak temperature occur at about 1.8xR

21 Outline Japan (LLE) Study of the superpenetration mechanism for fast ignition -super penetration penetration in preformed plasma -super penetration in an implosion US Electron transport and isochoric heating US Proton focusing and isochoric heating Future prospects in the US and Japan

22 New US and Japanese facilities in 2007/8 will support proof of principle studies of fast ignition lz-pw FY06-2 kj/5ps SNL Z Beamlet / Z l10 kj/10ps, 10 kj/2 ns lomega-ep FY06-2 beams 2.6 kj/ps, Firex I Omega EP lnif-pw - 3 kj/10 ps HEPW at NIF

23 Conclusions Fast ignition has important potential Both electron ( cone guided and super-penetration) and proton ignition are being studied The physics is challenging and interesting New facilities for integrated experiments and improved modeling should clarify the feasibility of FI in the next several years