Fast ignitor research at the Institute of Laser Engineering, Osaka University

The physics element relevant to the fast ignitor in inertial confinement fusion has been extensively studied. Laser-hole boring with enormous photon pressures into overcritical densities was experimentally proved by density measurements with XUV laser probing. Ultra-intense laser interactions at a relativistic parameter regime were studied with a 50-TW glass laser system and a 100-TW glass laser system synchronized with a long pulse laser system. In the study of relativistic laser beam propagation in a 100-mum scale-length plasma, a special propagation mode (super-penetration mode) was observed, where the beam propagated into overdense regions close to the solid target surface. At the super-penetration mode, 20% of the laser energy converted to energetic electrons toward the target inside, while the coupling efficiency was 40% without the long scale-length plasmas. The high-density energetic electron transport and heating of solid material was also studied, indicating beamlike propagation of the energetic electrons in the solid target and effective heating of solid density ions with the electrons. Based on these basic experimental results, the heating of imploded plasma by short-pulse-laser light with three different ways of injecting the heating pulse has been studied. (C) 2001 American Institute of Physics.