Quantification and Assessment of Radiation-Trapping Efficiency in Inertial Confinement Fusion Implosion Experiments with High-Z–Lined Single-Shell Targets

Achieving high-temperature “volume-burn” ignition conditions in inertial confinement fusion implosions requires a shell that contains the DT fuel and, at the same time, minimizes the escape of thermal energy from the fuel in the run-up to ignition conditions. Volume burn involves the entire fuel mass igniting at once, as opposed to ignition by a propagating burn wave, as in conventional cryogenic shell implosions. Single-shell “pushered” implosions utilize an opaque high-Z inner shell lining to “trap” the radiation that would otherwise escape and cool the fuel. We employ radiation-hydrodynamic simulations, utilizing enhanced radiation visualization tools to arrive at a meaningful measure of the effectiveness of radiation trapping. The radiation energy density of the fuel is a meaningful ignition parameter only if the fuel mass is optically thick. The radiative flux that escapes the fuel is a more important consideration than the radiation energy that may be trapped in the fuel. Opaque shell linings are strong absorbers, not mirrors, and they reduce fuel cooling only to the extent that they retard the escaping energy flux. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0003856.