Effect of soft and hard x-rays on shock propagation, preheating, and ablation characteristics in pure and doped Be ablators

Abstract

Detailed investigations are carried out on shock, preheat, and ablation characteristics in x-ray driven beryllium based targets, a candidate ablator material for many inertial confinement fusion studies due to its high mass ablation rate. The study involves extensive radiation hydrodynamic simulations performed on pure and 1% copper doped beryllium foils irradiated by a temperature drive source consisting of both Planckian and Gaussian distributions with peaks lying in soft and hard x-ray regions, respectively. The results of steady state x-ray driven ablation and radiant heat exchange in a sub-critical shock are extended to a non-Planckian source. Based on that, new scaling relations are proposed for shock velocity, shock breakout temperature, maximum preheat temperature, and mass ablation rate with the temperature ( 120 - 200 eV) and the fraction of total energy density due to Gaussian distribution ( 0 - 0.25) of the incident drive. All parameters increase with drive temperature strength, but the presence of hard x rays does not affect them uniformly. Among all, preheat and shock breakout temperature exhibit a strong dependence on fraction of hard x rays present in the drive spectrum. The effect of doping translates into a pronounced decrease in preheat and shock breakout temperature, while mass ablation rate reduces marginally. The resulting variations in different parameters are explained on the basis of distribution of total extinction coefficient over the spectral form of an incident drive source.