Detailed simulations of the first deuterium-tritium-filled double shell implosions on the National Ignition Facility

The first indirectly driven, liquid DT-filled double shell inertial confinement fusion (ICF) implosions have recently been successfully performed on the National Ignition Facility (NIF). Double shells are a class of alternative designs that use a low-Z outer shell to compress a foam cushion that accelerates a high-Z inner shell to efficiently compress a liquid DT core. Double shells are challenging to fabricate, field, and model. Important engineering features enabling double shell fabrication include a fill-tube penetrating all shells and a carefully designed and very narrow (few μm) step-joint in the ablator. Due to the higher density materials involved, high Atwood number instabilities are also important at many material interfaces. In this paper, numerical simulations of double shell implosions using the Los Alamos National Laboratory multi-physics radiation-hydrodynamics code xRAGE will be discussed. An extensive effort has been under way for several years to develop the code capabilities for ICF simulations in a common modeling framework to allow ease of simulation setup and standardization of the computational methodology. This paper will present a wide range of simulation results capturing, quantifying, and comparing the impact of all these degradation mechanisms on implosion performance. Brief comparisons with recent experimental results and suggestions for future improvements will also be discussed. Our results suggest that capsule surface roughness and the step-joint gap have the largest impact on implosion performance. Initial experimental data may suggest that the sensitivity to the step-joint gap could provide the dominant explanation for DT-filled double shell experiments that have been fielded on NIF thus far.. Authors: Scott, Ryan Lauritz [Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)] (ORCID:0009000276205195); Robey III, Harry F. [Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)] (ORCID:0000000151698283); Haines, Brian Michael [Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)] (ORCID:0000000238897074); Lester, Ryan Stuart [Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)] (ORCID:0000000245883690); Sauppe, Joshua Paul [Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)] (ORCID:0000000215071595). DOE Contract: 89233218CNA000001. Subjects: 70 PLASMA PHYSICS AND FUSION TECHNOLOGY; Double Shell; NIF; National Ignition Facility; degradation mechanism; fill tube; fill-tube; step joint; step-joint; surface roughness