Analysis of radiation symmetrization in hohlraum targets

Abstract

Symmetrization of illumination nonuniformity by thermal radiation in spherical hohlraum targets has been studied systematically for indirectly driven inertial confinement fusion. Numerical calculations have shown that the effect of X-ray re-emission on the illumination uniformity is quasi-linear. On the basis of a linear theory it is found that the nonuniformity of each mode of the X-ray source is considerably smoothed out by three different effects. The first is the geometrical effect, which accounts for the configuration and the number of X-ray converters. The second is the effect of single emission, which depends only on the hohlraum structure (area ratio). The third is the effect of multiple re-emission, which is equal to the reciprocal of the average circulation number of radiation in a hohlraum target. The author gives practical solutions regarding the required number of converters, Nc, in particular for heavy ion fusion systems. It is shown that Nc = 6 (hexahedron) is a necessary and sufficient condition to ensure tolerable symmetrical illumination (⩾ 1-2% rms)