HIGH-CONVERGENCE UNIFORM IMPLOSION OF FUSION PELLETS WITH THE NEW GEKKO LASER

The irradiation uniformity of the GEKKO XII laser has been improved by implementing the state-of-the-art beam smoothing and laser control te chniques in the system. Non-uniformity modes higher than 20 are improv ed to less than 1% RMS by introducing partially coherent light, while the lower modes are improved to 3-4% RMS. Implosion experiments were c arried out with the new GEKKO XII: a fast-rise square pulse preceded b y a pre-pulse was used to suppress the Rayleigh-Taylor instability at the acceptable expense of implosion efficiency. The experimental resul ts are compared with a pusher-fuel mixing model combined with a one-di mensional hydrodynamic simulation. The degradation of experimentally o btained neutrons is mainly attributed to the lower-mode asymmetry. Rec ent results of planar target experiments on hydrodynamic instabilities are also presented. Particular emphasis is given to the noticeable re duction of fluid instability by the flushing of an external x-ray over the target surface prior to the main drive pulse, leading to suppress ion of the initial imprint amplitude by the pre-formed plasma.