Radiative properties and line trapping effects in post-explosion inertial fusion plasmas

Abstract

Radiative transfer will play a major role in energy transport within post-explosion inertial confinement fusion (ICF) plasmas. The physical processes affecting radiative energy transport in such moderate-density plasmas are qualitatively different from those of many higher-opacity laboratory plasmas, and reliable analyses of their radiative properties require the use of relatively detailed physical models. In this paper, the radiative processes of plasmas generated by high-gain inertial fusion pellet explosions are investigated. A nonlocal thermal dynamic equilibrium (LTE) radiative transfer/ionization balance code is used in which steady-state ionization and excitation populations are calculated by solving multilevel atomic rate equations self-consistently with the radiation field. It is shown that for much of their hydrodynamic evolution these plasmas are often optically thick to line radiation, but optically thin to the bulk of the continuum radiation. Because of this, line trapping—i.e., the self-attenuation of line radiation in their optically thick cores—plays a critical role in both altering the atomic level populations and in significantly reducing the escaping radiation flux. Results are compared with those obtained using thermal equilibrium, LTE, optically thin, and multigroup radiation diffusion models. Also discussed are the ramifications of the present results for radiation-induced damage in high-gain ICF facilities.