Recent progress of implosion experiments with uniformity-improved GEKKO XII laser facility at the Institute of Laser Engineering, Osaka University

Abstract

The irradiation uniformity of the GEKKO XII laser [C. Yamanaka et al., IEEE J. Quantum Electron. QE-17 1639 (1981)] has been improved by using partially coherent light with angular spectral dispersion and by improving power balance among the beams. Implosion experiments with the uniformity-improved GEKKO XII have been carried out in order to demonstrate stable formation of the hot spark. The isentrope of the compressed pellet shell is controlled by adding a prepulse to enhance the ablative stabilization of the Rayleigh–Taylor instability. The implosion dynamics 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, recent results of planer target experiments on the ablative stabilization of the Rayleigh–Taylor instability are also presented. The observed linear growth rate was about 50% of the classical growth rate and was lower than that of the theoretical prediction, based on the Takabe formula combined with the one-dimensional simulation.