Recent Progress of Fast-Ignition Project in Osaka University (FIREX)

1. Recent Progress of Fast-Ignition Project in Osaka University (FIREX) Shinsuke Fujioka, Institute of Laser Engineering, Osaka University 2010.3.11

2. Contributors S. Fujioka, H. Shiraga, N. Miyanaga, J. Kawanaka, K. Tsubakimoto, Y. Fujimoto, N. Morio, S. Matsuo, Y. Kawakami, K. Kawabata, H. Yamamoto, T. Jitsuno, Y. Nakata, K. Shigemori, T. Kawasaki, K. Sawai, H. Murakami, K. Ueda, S. Takamiya, Y. Kubota, N. Sarukura, T. Shimizu, K. Suzuki, S. Urushihara, H. Oku, K. Hashimoto, K. Torimoto, A. Fujita, H. Hasegawa, H. Fujita, Y. Kitamura, H. Matsuo, T. Sakamoto, T. Sezaki, S. Yanagida, M. Koga, O. Maegawa, K. Shimada, S. Okajima, M. Arai, K. Ishii, M. Hatori, H. Nakamura, T. Watari, H. Hosoda, Y. Arikawa, H. Kikuchi, T. Nagai, H. Nishimura, T. Ueda, S. Ohira, Y. Sakawa, K. Tanaka, H. Habara, S. Tanimoto, S. Hino, K. Shimada, K. Kida, T. Iwawaki, T. Norimatsu, M. Nakai, H. Homma, H. Hosokawa, M. Nagata, H. Kadota, K. Fujioka, H. Kaneyasu, Y. Suzuki, H. Nagatomo, T. Johzaki, M. Murakami, M. Murakami, K. Mima, H. Azechi Osaka University, Japan A. Sunahara Institute for Laser Technology, Japan H. Sakagami, T. Ozaki, A. Iwamoto National Institute for Fusion Science, Japan T. Taguchi Setsunan University, Japan Y. Nakao Kyusyu University, Japan M. Key Lawrence Livermore National Laboratory, USA P. A. Norreys Central Laser Facility, UK J. Pasley University of York, UK

3. Summary The most important physics related to the fast-ignition should be clarified in the FIREX project until FY2011. • One beam of the high power PW laser (LFEX) carries < 6 x 1018 W/cm2 of the peak intensity, integrated fast-ignition experiment is in progress with the LFEX laser. • Neutron yield was increased by a factor of 30 by the fast heating. • Coupling efficiency between heating laser (LFEX) and fuel was low (< 5%), because the inside of cone is filled with preformed plasma generated by pedestal (~ 3 ns, > 1013 W/cm2) of the LFEX pulse. • Another one beam of the LFEX will be in operation in FY2010. Next campaign of the integrated FI experiment will start on August.

4. Compression and heating are separated in fast ignition scheme. ILE, Osaka Ignition & Burning Heating Compression Demo. in 1991 @OSAKA, JP To be demo. in 2011 @OSAKA, JP To be demo. in 2011 @LIVARMORE, USA

5. One beam of the LFEX laser is in operation. Another one beam will be in operation inFY2010. ILE, Osaka Sensor 3 2x2 Focusing optics (2F) 2x2 Output from amplifier Sensor 1 Beam transport optics (2F 1F) 1x4 Pulse compressor (1F)

6. Fast-ignition experiment, which was stopped since 2002, was restarted in 2009. ILE, Osaka Jun, 2002 0.5 keV heating with PWL Feb, 2004 Construction of LFEX laser was started Mar, 2005 First light of LFEX laser Feb, 2007 Output Energy 2.9 kJ/beam@Broadband was achieved Feb, 2008 Target irradiation with compressed beam was started Nov, 2008 Precision alignment of pulse compressor Dec, 2008 Target irradiation with high-power beam was started Feb, 2009 Irradiation of Fast Ignition (FI) target was started Jun, 2009Integrated FI experiment (5 ps, < 2 x 1018 W/cm2) Sep, 2009Integrated FI experiment (1 ps, < 6 x 1018 W/cm2)

7. Fuel capsule attached with a cone is compressed by GEKKO XII laser and heated by LFEX laser. ILE, Osaka Compression Laser GEKKO-XII Fusion Fuel Heating Laser LFEX Shell Diameter 500 µm Thickness 7 µm Material CD plastic Cone Angle 45 deg. Material 7 µm gold Tip size 30 µm Beam# 1 beam Energy 100 -800 J Spot size 40 µm Duration 1 or 5 ps Wavelength 1053 nm Beam# 12 beams Energy 280 J/beams (2.5 kJ total) Duration 1.5 ns (Flat top) Wavelength 527 nm

8. One oscillator was used for GEKKO-XII and LFEX, which are synchronized with an accuracy of 20 ps. ILE, Osaka DA 400S DA 400S DA 400S DA 400S DA 400S RA 50 RA 50 RA 50 RA 50 RA 50 RA 50 RA 50 LFEX laser LFEX laser LFEX laser DFM 75 DFM 75 DFM 75 DFM 75 DFM 75 DFM 75 OS 75S OS 75S OS 75S OS 75S OS 75S OS 75S OS 75S SF 400S SF 400S SF 400S SF 400S SF 400S DFM １25 DFM １25 DFM １25 OS 125S OS 125S OS 125S RA 50 LFEX laser GEKKO XII

9. Many aspects of fast-heating plasma were measured with diagnostic technique. ILE, Osaka X-ray streak camera Imp./heating timing Neutron detector Diagnostic of fusion reaction Space Time (ns) X-ray pinhole camera viewing inside of cone Hard x-ray camera identifying reaction region X-ray framing camera implosion plasma diag.

10. Neutron yield was increased by increasing in heating laser intensity by shortening pulse duration. ILE, Osaka S. Fujioka Neutron yield v.s. heating energy 1 ps (< 6 x 1018 W/cm2) 5 ps (< 2 x 1018 W/cm2) Neutron yield w/o heating 1 x 104 Heating laser (LFEX) energy [J]

11. Coupling efficiency between heating laser and fuel is quite low compared to the PW experiment. ILE, Osaka S. Fujioka Relation between ion temperature and laser energy Goal PWL(0.6 ps) 15 – 20% coupling eff. LFEX(1 ps) <5 % of coupling Ion temperature (keV) LFEX(5 ps) Heating laser energy (J)

12. Slope temperature of fast electrons is relatively high compared to that obtained in the PW experiment. ILE, Osaka S. Fujioka Hot electron temperature v.s. laser intensity L1406 L1404 Scaling by Pukov (Assuming scale length L = 30 µm) Slope temperature of hot elelctron (MeV) L1402 L1408 L1405 L1411 Ponderomotive scaling scaling obtained in PW experiment Laser intensity (a.u.)

13. Electron acceleration may be occurred in a preformed plasma inside a cone. ILE, Osaka S. Fujioka Laser pulse shape 1. main pulse ~ 1019 W/cm2 a few ps（FWHM） Log (laser intensity) 2. pedestal > 1010 W/cm2 a few ns (FWHM) Time pedestal >1010 W/cm2→forming pre-plasma in cone →accelerating electrons in plasma →increasing too hot electrons→reducing coupling

14. Does the ring-shape emission imply that the inside of the cone was filled with preformed plasma ? ILE, Osaka X-ray pinhole camera viewing inside of cone

15. Density scale length of a preformed plasma, observed by using side-on x-ray backlighting, is > 50 µm. ILE, Osaka S. Fujioka LFEX Laser Backlighter ~ 2.7keV -0.91 ns LFEXLaser Au Plate 20.9° -0.61 ns Backlight w/plasma X-ray streak camera -0.30 ns 1 ns LFEX 500 μm

16. Monochromatic x-ray imaging technique is used to measure areal density of the compressed fuel. ILE, Osaka S. Fujioka Schematic of diagnostics 2100 mm X-ray Framing Camera Spherical bent crystal Monochromatic x rays：2.7 keV M = 20 Main Target 105 mm Laser: 1 kJ/ns in 2w Time 3 mm CHClBacklighter Crystal spec.(SAINT-GOBAIN) Material: Quartz（21-33） Radius : 200 mm Bragg angle : 83.01° Photo energy： 2.7 keV (Vanadium - Hea) Framing image

17. Self-emission image was not superimposed on a shadow image obtained with monochromatic imager. ILE, Osaka S. Fujioka - 400 ps shadow image of mesh Max. compression MTF v.s. wavlength + 200 ps 13µm 0.1

18. Heating up to ignition temperature (5 keV) should be demonstrated until FY 2011. ILE, Osaka Dec, 2008 Target irradiation with high-power beam started Feb, 2009 Irradiation of Fast Ignition (FI) target started Jun, 2009 FI integrated experiment with 1-beam LFEX late 2009 Multi-beam compression and focusing Beam combining early 2010 FI integrated experiment with multi-beam LFEX Test of various advanced target concepts 2011 Demonstration of ignition temperature with FI

19. Summary The most important physics related to the fast-ignition should be clarified in the FIREX project until FY2011. • One beam of the high power PW laser (LFEX) carries < 6 x 1018 W/cm2 of the peak intensity, integrated fast-ignition experiment is in progress with the LFEX laser. • Neutron yield was increased by a factor of 30 by the fast heating. • Coupling efficiency between heating laser (LFEX) and fuel was low (< 5%), because the inside of cone is filled with preformed plasma generated by pedestal (~ 3 ns, > 1013 W/cm2) of the LFEX pulse. • Another one beam of the LFEX will be in operation in FY2010. Next campaign of the integrated FI experiment will start on August.