Coronal Physics Modeling in Wetted-Foam Targets Proposed for Neutron Sources at the National Ignition Facility

The potential application of wetted-foam, direct-drive deuterium–tritium (DT)-filled targets for producing large neutron yields at the National Ignition Facility[1] has stimulated recent multi-laboratory interest in the development of these targets. The DT-wetted foam, ideally the primary ablator, is, however, surrounded by a CH layer that can be the dominant absorption medium for much of the laser pulse. This work used the hydrodynamics code SAGE to model two near-term wetted-foam designs and the design of Ref. 1 in polar-direct-drive geometry, looking at the transition between CH and D₂/DT in the absorption region. It is found that this transition does not occur in an abrupt manner but is spread over a significant time interval—this behavior being understood to result from the absorption being spread over a large range of densities. This understanding is supported by a comparison between observed and simulated time-dependent scattered light in a related experiment (N230131-002)[2] that used a 3-mm-diam, 18-µm-thick CH shell filled with liquid D₂. This material is based upon work supported by the Department of Energy [National Nuclear Security Administration] University of Rochester “National Inertial Confinement Fusion Program” under Award Number DE-NA0004144.

[1] R. E. Olson et al., Phys. Plasmas 28 (2021).

[2] G. E. Kemp et al., “Exploration of Polar Direct Drive Wetted Foam Concepts for Neutron Sources on the National Ignition Facility Laser,” to be submitted to Physics of Plasmas.