High-convergence uniform implosion of fusion pellets with the new GEKKO laser

Abstract

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