Impact of hohlraum cooling on ignition metrics for inertial fusion implosions

Abstract

This paper extends the evaluation of ignition metrics to include the impact of hohlraum cooling before peak implosion velocity in radiation driven implosions. First, we provide an extension of the results for the key hot spot stagnation quantities from the 2018 paper [Lindl et al., Phys Plasmas 25, 122704 (2018)]. The modified analytic expressions presented here match the Hydra results for these National Ignition Facility scale implosions both with and without hohlraum cooling before peak velocity if the effective ablation pressure Pabl(effective) = Pabl(tpv − 0.5 ns) is used in the analytic formulas, where tpv is the time of peak implosion velocity. Second, we provide an analysis that enables a comparison of the Hydra radiation hydrodynamics code calculations utilized here with the predictions of the analytic piston model [Hurricane et al., Phys. Plasmas 29, 012703 (2022)] of an ICF implosion, which focused on sensitivity to time duration of the hohlraum cooling phase before peak velocity (often called the “coast time”) and the shell radius at peak velocity Rpv. Third, we provide a set of ignition metrics that are valid across a wide range of capsule designs valid for implosions both with and without hohlraum cooling before peak implosion velocity is reached.