Measurements of freely-expanding plasma from hypervelocity impacts

This paper details initial results from a study of electrical effects resulting from hypervelocity impacts at a Van de Graaff dust accelerator. Iron particles between 10−15 g and 10−10 g in mass were impacted on several different metallic targets at speeds of 1 km/s to 50 km/s. The goal of this study is to characterize the impact-generated plasma and associated RF emission. Results are presented from data collected using retarding potential analyzers. The rate of signal detection was found to have a dependence both on material and on target bias. From a single analyzer, some signal waveforms exhibited oscillatory behavior which is significant in determining the effect of impacts on spacecraft. Using two analyzers at different distances from the target, the expansion speed of the impact plasma was measured to be between 10 km/s and 30 km/s.