Ejecta Production from Second Shock: Numerical Simulations and Experiments

From detailed numerical simulations and comparison with recent experiments, we explore ejecta production at an interface that is impulsively accelerated by two successive shock waves. The perturbed material interface demarcates the boundary between a metal and vacuum resulting in the formation of ejecta driven by the Richtmyer–Meshkov instability. The numerical simulations were performed with the astrophysical FLASH code, in which the shocked metallic response is conceptually modeled using continuum hydrodynamics. The experimental data were obtained from a two-shockwave, high-explosive tool at Los Alamos National Laboratory capable of generating ejecta from a shocked Sn surface in to a vacuum. In both the simulations and the experiment, linear growth is observed following the first shock event, while the second shock strikes a finite-amplitude interface leading to nonlinear growth. The timing of the second incident shock was varied systematically in our simulations to realize a finite-amplitude re-initialization of the RM instability driving the ejecta. We take advantage of the nonlinear growth following the second shock, to evaluate a recently proposed model for sourcing of mass in ejecta formation that accounts for shape effects through an effective wavelength. In particular, we find the agreement between simulations, experiments and the mass model is improved when such shape effects associated with the interface at the instance of second shock are incorporated. The approach outlined here of combining continuum simulations with validated nonlinear models can aid in the design of future experimental campaigns.