Radiation and Heat Transport in Divergent Shock-Bubble Interactions*

Shock-bubble interactions (SBI) are important across a wide range of physical systems. At high energy densities, interactions between laser-driven shocks and micro-voids in ICF ablators generate instabilities that are a major obstacle in achieving ignition. Experiments imaging the collapse of such voids are constrained by spatial and temporal resolution. In this study, we use the hydrodynamic code xRAGE to understand the evolution of a collapsing mesoscale void by revealing dynamics at timescales shorter than experimental imaging framerates. We examine the role of radiation and thermal transport in the evolution of the SBI and benchmark several transport models and parameters against experimental results. We find that a gray radiation diffusion model is sufficient to reproduce empirical shock pressures within experimental error, and that radiation lowers shock pressures by providing an additional energy sink in the ablation region and in the shock front. Employing a flux-limited Spitzer model for heat conduction, we find that flux limiters between 0.03 and 0.10 produce agreement with experimental pressures. This insensitivity suggests that the system is well-within the Spitzer regime. Higher heat conduction is found to lower temperatures in the ablated plasma, resulting in lower pressures at late times. Finally, we confirm that the instabilities observed are baroclinically driven.