Dust and atmospheric influence on plasma properties observed in light gas gun hypervelocity impact experiments

Abstract

Plasma and associated radio frequency (RF) emission produced by hypervelocity impacts of dust and meteoroids are a source of scientific information on stellar dust populations and a potential hazard to spacecraft electrical systems. A previously unexplored aspect of these impacts is the influence that non-vaporized ejecta, or dust, can have on both the plasma and RF emission. Although initially neutral, this dust can gain a charge through collisions with the plasma potentially forming a dusty plasma. Characterizing dust-producing impacts allows for assessing the threat they pose to spacecraft. This paper investigates the influence that a 0.5 Torr background pressure and dust had on the plume evolution of ground-based hypervelocity impact experiments. The effects of material and target charge on dust production and dynamics were explored. Faraday cup plasma sensors were designed and built specifically for these experiments to capture the distribution of charge in the plume and record highly transient charged dust detections. We found that the background gas had a significant effect on the propagation and evolution of the impact plume, slowing the plume from its jetting velocity of 16 km/s down to 10 km/s leading to a Rayleigh-Taylor instability. Charged dust was confirmed by the Faraday cup measurements. Based on high-speed imagery, we observed that plasma was dragged along the trajectory of the expanding dust curtain. The measured signal from this dragged plasma lasted for 10 times longer than plasma that did not contain dust. Plasma with dust was highly negative with current densities measured by the plasma sensors of up to 0.1 A/m2 — 10 to 1000 times more dense than measured on sensors at other elevations — putting spacecraft electronics at greater risk of RF interference and electrical discharges.