High energy density reshock experiments at the National Ignition Facility

A series of experiments at the National Ignition Facility studying the hydrodynamic instability of reshocked high energy density (HED) mixing regions is reviewed. Laser-driven blast waves are propagated into opposite ends of a planar target consisting of a high-density plastic adjacent to a low-density foam with a machined perturbation at the interface. The first blast wave travels from the plastic into the foam (heavy-to-light), which creates an unstable plasma interface with the machined initial condition that grows by the Richtmyer–Meshkov and Rayleigh–Taylor instabilities. Once the interface has become nonlinear, the second blast wave reshocks the interface in the opposite (light-to-heavy) direction. After reshock, the instability growth progresses at a faster rate, similar to what is seen in classical Richtmyer–Meshkov shock tube experiments using gases. The experiments suggest that reshocking a nonlinear interface accelerates the transition to turbulence and provides a way to access fully developed turbulent regimes within the short time duration of an HED experiment. The experimental design, experimental data, simulations for single-mode and multimode initial conditions, and implications for validating Reynolds-averaged turbulence models in the HED regime are discussed.