Hydrodynamics of Void Collapse

Voids are low-density regions in an otherwise homogeneous higher-density medium. The hydrodynamics of a collapsing void are important across a wide range of physics, including planetary science, astrophysics, nuclear fusion, and materials science. In the high energy density regime, instabilities generated by collapsing voids are a major challenge in the pursuit of fusion ignition. Void collapse is highly non-linear, involving shock reflection, refraction and focusing which results in the formation of plasma jets and phase transformation in the surrounding material. Experiments imaging the shock-induced collapse of voids are underway, but are constrained by spatial and temporal resolution. In this study, we use xRAGE, a Los Alamos National Laboratory radiation-hydrodynamic code, to understand the evolution of a collapsing void by revealing dynamics at timescales shorter than experimental imaging framerates. These simulations reveal separation and acceleration of the shock front as it transits the void, creating an inward pressure gradient in its wake which leads to the development of instabilities at the former void's edge.