Thick-shell model of indirect-drive yield sensitivity

Abstract

We present an analytic thick shell model for indirect-drive ICF implosions that starts by using the Rocket equation to evaluate peak fuel kinetic energy and hence by energy balance, stagnated fuel internal energy. We then use the approximation of the hot spot decelerating adiabatically to an isobaric stagnated state coupled to a self-consistently calculated fuel aspect ratio. The model, validated by 1D radiation-hydrodynamics simulations, provides sensitivities of indirect-drive yield, DSR and ignition metrics to a host of initial and final state capsule and hohlraum parameters, applicable to the current relevant regime of igniting implosions. The model is used to highlight parameter trade-offs and estimate expected sensitivity in 1D compression, stagnated areal density and yield at current and higher performance levels. Several new insights are presented. Of note, we explain the weak dependence of ablator thickness on implosion velocity for designs with buried dopant layers, the uncertainty in performance improvement when adding fuel or reducing initial hot spot density, and the role of ionization energy and albedo in setting ablator efficiency.