Implosion and heating experiments of fast ignition targets by Gekko-XII and LFEX lasers

¹ Institute of Laser Engineering, Osaka University, Suita, Osaka 565-0871, Japan
² Nationai Institute for Fusion Science, Toki, Gifu 509-5292, Japan
³ Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871, Japan
⁴ Lawrence Livermore National Laboratory, Livermore, California 94550, USA
⁵ Rutherford Appleton Laboratory, STFC Rutherford Appleton Laboratory, Harwell Oxford, Didcot, Oxfordshire OX11 0QX, UK
⁶ York Plasma Institute, Department of Physics, University of York, York YO10 5DQ, UK
⁷ Institute for Laser Technology, Suita, Osaka 565-0871, Japan
⁸ Faculty of Science and Engineering, Setsunan University, Neyagawa, Osaka 572-8508, Japan
⁹ Graduate School of Engineering, University of Fukui, Fukui, Fukui 910-8507, Japan
¹⁰ Kansai Photon Science Institute, Japan Atomic Energy Agency, Kizu, Kyoto 619-0215, Japan

^a e-mail: shiraga@ile.osaka-u.ac.jpr

Published online: 15 November 2013

Abstract

The FIREX-1 project, the goal of which is to demonstrate fuel heating up to 5 keV by fast ignition scheme, has been carried out since 2003 including construction and tuning of LFEX laser and integrated experiments. Implosion and heating experiment of Fast Ignition targets have been performed since 2009 with Gekko-XII and LFEX lasers. A deuterated polystyrene shell target was imploded with the 0.53- μm Gekko-XII, and the 1.053- μm beam of the LFEX laser was injected through a gold cone attached to the shell to generate hot electrons to heat the imploded fuel plasma. Pulse contrast ratio of the LFEX beam was significantly improved. Also a variety of plasma diagnostic instruments were developed to be compatible with harsh environment of intense hard x-rays (γ rays) and electromagnetic pulses due to the intense LFEX beam on the target. Large background signals around the DD neutron signal in time-of-flight record of neutron detector were found to consist of neutrons via (γ,n) reactions and scattered gamma rays. Enhanced neutron yield was confirmed by carefully eliminating such backgrounds. Neutron enhancement up to 3.5 × 10⁷ was observed. Heating efficiency was estimated to be 10–20% assuming a uniform temperature rise model.