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

The first indirectly driven, liquid DT-filled double shell ICF implosions have recently been successfully performed on the National Ignition Facility. Double shell implosions are of interest, as they provide an alternate approach to ignition, enable the study of different physics, and present new challenges as compared to the more well studied case of single shell implosions. Double shells operate in volume ignition mode, due to the increased radiation trapping inside the high-Z inner shell, as opposed to central hot spot ignition, which is used in single shell implosions. Double shells are challenging to fabricate, field, and model as they involve multiple concentric shells (Al ablator, low-density CH intra-shell foam, CH tamper, Mo inner shell) surrounding a central liquid DT fuel volume. Several engineering features are necessary on these capsules beginning with a fill-tube penetrating all shells to allow for DT filling. In addition, the outer Al ablator is fabricated in two halves and is assembled with a carefully designed and very narrow (few µm) step joint. Due to the higher density materials involved, high Atwood number instability and mix is also important at many of the material interfaces. In this talk, numerical simulations of double shell implosions using the LANL multi-physics radiation hydrodynamics code xRAGE will be discussed. An extensive effort has been underway for several years to develop the code capabilities for ICF simulations in a Common Modeling Format (CMF) to allow ease of simulation setup and standardization of the computational methodology. This talk will present a wide range of simulation results capturing, quantifying, and comparing the impact of all these degradation mechanisms on implosion performance. Comparisons with recent experimental results and suggestions for future improvements will be discussed as well.