Pulse shaping with plastic ablators to overcome unique challenges with indirect-drive double shell inertial confinement fusion

Current double shell inertial confinement fusion (ICF) experiments at the National Ignition Facility drive the implosion of an outer Al (ablator) shell using a very high-adiabat, single shock pulse shape. This shock is launched into the outer shell by thermal x-rays created from a laser-driven Au hohlraum surrounding the capsule. Recent simulations and experiments have shown that the Al outer shell is susceptible to target imperfections such as intermediate wavelength surface roughness and the assembly joint required to place a metal inner shell inside. To reduce design sensitivity to these imperfections we are exploring the use of alternate ablator materials and pulse shaping. Specifically, integrated hohlraum simulations predict that hard x-rays from Au M-shell radiation created at the hohlraum walls can preheat the plastic ablator to several eV, which will cause rapid closure of the ablator assembly joint. Furthermore, for our existing pulse shapes, plastic is predicted to have significantly greater ablative stabilization of Rayleigh-Taylor growth compared to Al. In this talk we will present simulations assessing the predicted performance of both Al and plastic double shell ablators, as well as address key questions regarding impact of increased M-band preheat.