Study on size of laser entrance hole shield for ignition octahedral spherical hohlraums

Abstract

AbstractIn this paper, the influences of laser entrance hole shields on capsule symmetry and coupling efficiency of an ignition octahedral spherical hohlraum are studied using analytical model and three-dimensional Monte-Carlo simulations. As a result, there are two critical shield radii at which the capsule asymmetry tends to minimum, and the coupling efficiency from hohlraum to capsule reaches its maximum when the shield size is taken around the second critical radius. For the ignition octahedral hohlraums used in our study, the first critical radius is 0.625 mm with a capsule asymmetry of 0.24%, and the second is 0.86 mm with 0.26%, and the asymmetry is smaller than 0.58% for shields’ radius in the range of 0.44 and 0.88 mm, which therefore leaves much flexibility in the shield radius design even the shields have an expansion under radiation ablation. The initial shield radius can be taken around the first critical radius in the ignition target design, not only to have a minimum initial capsule radiation asymmetry, but also to get a minimum asymmetry and highest coupling efficiency during the main pulse of drive. Finally, the relative flux of laser spot, wall and shields is 2.2:1:0.6 for our ignition octahedral spherical hohlraum model from the Monte-Carlo simulations.