Indirect-direct hybrid target experiments with the GEKKO XII laser

Abstract

A new fusion capsule drive scheme was investigated. The capsule isilluminated by a low intensity thermal X ray pulse prior to themain drive pulse. This leads to a noticeable suppression of initialimprinting by the drive beam because of thermal smoothing in thepreformed plasma. Of the several types of indirect-direct hybridtarget, the authors investigated the hybrid effect for two types. One is afoam hybrid, in which the fuel capsule has a low density foam layerattached directly on its surface and where pulsed radiation generated from athin high Z layer on the foam propagates through the foam, creating apreformed plasma. The other is an external hybrid, in which the capsuleis illuminated by external X ray radiationgenerated using different beams from the capsule drive beams. Thehybrid effect was demonstrated for both types by imposing an initialimprint on a planar target with an intensity modulated beam, andsubsequent non-uniformity growth due to Rayleigh-Taylor instability wasobserved by means of face-on backlighting. The observed suppression due tothe presence of the preformed plasma is interpreted by a cloudy day modelfor both hybrids. Capsule implosion experiments have also been started. The overall implosion dynamics observed is replicated by 1-Dhydrocode simulations. Preliminary results from the implosionexperiments are presented.