Numerical simulation of performance metrics and trends in double shell implosions on the National Ignition Facility

Double-shell ICF implosions have recently begun on the National Ignition Facility (NIF) and are now being routinely performed to both improve performance as well as to study sensitivities to capsule shell materials, engineering defects (fill-tube, step-joint, surface roughness, etc.), and increasing laser power and energy. Double shells are of interest as they operate in volume ignition mode as opposed to hot-spot ignition mode for single shells, and they emphasize different physics including enhanced radiation trapping by the higher-Z inner shell (Mo or W) as well as strong interfacial mixing at the multiple high Atwood number material interfaces. From the first double-shell shot on NIF (N240409), the yield has steadily increased (>10x) by a series of systematic changes to both the capsule and the driving laser. In this talk, we will compare data from the full NIF double-shell database (7 shots to date) with detailed simulations run with Los Alamos National Laboratory’s radiation-hydrodynamics code, xRAGE. This comparison is helping to quantify our understanding of these implosions as well as revealing the dominant sensitivities. The knowledge gained is being used to guide future experiments, suggest target improvements, and continue to improve our simulation capabilities.