The effects of target mounts in direct-drive implosions on OMEGA

The effects of two types of target mounts, stalks and spider silks, on the implosion of both room-temperature D-2-gas-filled shells and cryogenic D-2-ice-filled shells have been studied both experimentally and by means of two-dimensional simulations. The simulations indicate that the hydrodynamic effect of the expanding plasma created by the ablation of material from the target mounts and refraction of laser light by this plasma induce perturbations in the imploding shell that are damaging to the implosion. The spider silks are the more-damaging type of mount since the silks (typically four) are arrayed over the target surface, whereas the stalk (typically one) meets the target at a single point. Stalks are therefore preferred over silks as a target mount. The scale and magnitude of the perturbations induced by the spider silks have been verified by planar-target experiments performed on the OMEGA laser [T. R. Boehly, D. L. Brown, R. S. Craxton et al., Opt. Commun. 133, 495 (1995)]. The perturbations predicted by simulations to arise from stalks qualitatively agree with the results of implosion experiments using Ti-doped plastic shells. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3195065]