First Magnetized Hohlraum-Driven Implosions on the NIF

Magnetizing an ICF hotspot to reduce electron-thermal and fusion-alpha losses is an old idea to improve performance and reach ignition. A campaign is underway on NIF to study how an imposed axial magnetic field affects hohlraum-driven "symcap" (gas-filled) implosions. The goal is to demonstrate field compression in the implosion, and quantify its effect on the temperature and density of the hotspot, as measured by nuclear and x-ray output. Facility limitations require these shots to be room-temperature (not cryogenic) and use <~ 1 MJ of laser energy. Four shots have taken place as of June 2021. The two shots with no imposed field unfortunately had no capsule gas fill due to fielding issues, and thus no data on hotspot conditions. The other two shots had an imposed 26 T field at capsule center. They varied the hotspot self-emission shape from extremely prolate ("sausaged") to roughly round, by varying the ratio of powers on the NIF inner and outer beams. This standard method for tuning implosion shape on unmagnetized targets also works in magnetized ones. We hope to have an unmagnetized comparison shot before the APS meeting. I will review the results of these experiments, and radiation-magneto-hydrodynamic modeling of them with the LASNEX code.