Experimental Study of Ion Species Separation in Multi-Component Plasma Shocks

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Shock waves, frequently observed in air, also occur in high temperature gases where electrons have been liberated from ions, forming a plasma. This project will experimentally study shock waves by colliding plasma jets with stagnant plasma. When the plasma is composed of species of differing electric charge and mass, the rapid change in plasma properties across the shock wave can cause separation of these species, further complicating the shock structure. Understanding the physics present in these scenarios is important to furthering the understanding of astrophysical phenomena, including Type II supernova explosions, as well as the physics of implosions that occur in inertial-confinement fusion experiments. This project will collect detailed experimental data characterizing collisions between high-velocity multi-species plasma jets and stagnant plasma in an experiment where shock thickness is predicted to be large enough to be readily observable by diagnostic instruments.This project aims to experimentally identify shocks in multi-component plasmas in a parameter space where it is possible to resolve the structure of the ion shock layer. Interactions of collisional multi-species plasma jets with stagnated plasma will be studied in a regime where the mean-free-path is small enough for the jet interaction to be collisional yet large enough to attempt diagnosis of the shock structure over a few hundred mean-free-paths. The scope of the project will be to identify shocks formed during these interactions and investigate the parameter space to confirm whether the observed shocks are present in multi-ion-species plasmas. A series of multi-ion-species plasma jets will be emitted by a linear plasma-armature railgun. Shortly after the first jet stagnates against a barrier, the second jet will encounter the stagnant plasma at velocities sufficient to drive a shock in the plasma. A suite of diagnostics will be used to capture data indicating the presence of individual plasma species. The diagnostics that will be employed include (i) high spatial resolution survey spectroscopy to locate emission from ion species at the shock front and (ii) multi-chord interferometry which will be used in conjunction with spectroscopy to infer charge state and electron temperature in the shocked and unshocked regions. The experimental observations sought by this research have the potential to shed light on never-before-observed shock structures caused by collisional diffusion of ion species. This could enhance understanding of astrophysical phenomena and the physics of inertial fusion plasmas.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.