Heating of cryogenic targets in a light ion fusion cavity

Survivability of cryogenic targets in single-shot and reactor cavity environments is an essential prerequisite for high gain (>25) target experimentation, target development, and power production. Heat sources in a gas-filled light ion beam cavity include radiative, convective, and viscous heating by the cavity fill gas, heating due to laser radiation used to initiate low-density plasma channels for beam propagation, and heating due to ohmic due to ohmic dissipation of channel currents near the target. Prior to injection of the target into the cavity, tritium decay and target acceleration are the sources of heat. In this paper the parametric dependence, time scale, and magnitude of each of these thermal sources are discussed. Potential thermal protection techniques which may be applicable to long (>0.1 s), intermediate (approx. equal to ms), and short-duration (approx. equal to μs) heat loads are described, and remaining concerns are noted. (orig.)