Flow Collisionality Effects in Plasma Guns for Simulating Fusion Wall Response to Disruption Events

In this work, the suitability of a pulsed coaxial deflagration accelerator to simulate the interaction of edge-localized modes with plasma first wall materials is investigated. Suites of experimental diagnostics are used to characterize plume conditions in the Stanford plasma gun facility to quantify both the incident plasma heat flux and estimate the mean free path in the vicinity of stagnating surfaces. The process by which plasma jets stagnate on tungsten tokens is visualized using an ultra-high frame rate CMOS camera coupled to a Z-type laser Schlieren apparatus. Results indicate the formation of a strong extended bow shock that acts to redirect the flow away from the surface of the material. Measurements show that while sufficiently high plasma heat fluxes are achievable with gun devices (in excess of 10 GW m-2), significant differences in plasma density and temperature cause the formation of collisional fluid shocks that are not expected at similar timescales during ELM events in fusion conditions. Finally, MHD simulations are employed to quantify the shock shielding effect within the flow and how the strength of the diversion varies as the energy of impeding plasma jet changes.