RECENT PROGRESS OF IMPLOSION EXPERIMENTS WITH UNIFORMITY-IMPROVED GEKKO-XII LASER FACILITY AT THE INSTITUTE-OF-LASER-ENGINEERING, OSAKA-UNIVERSITY

The irradiation uniformity of the GEKKO XII laser [C. Yamanaka et al., IEEE J. Quantum Electron. QE-17 1639 (1981)] has been improved by usi ng partially coherent light with angular spectral dispersion and by im proving power balance among the beams. Implosion experiments with the uniformity-improved GEKKO XII have been carried out in order to demons trate stable formation of the hot spark. The isentrope of the compress ed pellet shell is controlled by adding a prepulse to enhance the abla tive stabilization of the Rayleigh-Taylor instability. The implosion d ynamics has been investigated by x-ray imaging and neutron diagnostics . The experimental results are compared with the mix model prediction based on the one-dimensional hydrodynamic simulation. The degradation of neutron yield is attributed to the low-mode asymmetry. Finally, rec ent results of planer target experiments on the ablative stabilization of the Rayleigh-Taylor instability are also presented. The observed l inear growth rate was about 50% of the classical growth rate and was l ower than that of the theoretical prediction, based on the Takabe form ula combined with the one-dimensional simulation. (C) 1996 American In stitute of Physics.