Electrical breakdown of anodized coatings in low-density plasmas

Abstract

A comprehensive set of investigations has been performed involving arcing on a negatively biased anodized aluminum plate immersed in a low-density argon plasma at low pressures (Po w 7.5X 10~ torr). These arcing experiments were designed to simulate electrical breakdown of anodized coatings in a low-Earth orbital environment. When electrical breakdown of an anodized layer occurs, an arc strikes, and there is a sudden flux of electrons accelerated into the ambient plasma. This event is directly followed by ejection of a quasineutral plasma cloud consisting of ejected material blown out of the anodized layer. Statistical analysis of plasma cloud expansion velocities has yielded a mean propagation velocity, v 19.4 ± 3.5 km/s. As the plasma cloud expands into the ambient plasma, energy in the form of electrical noise is generated. The radiated electromagnetic noise is detected by means of an insulated antenna immersed in the ambient plasma. The purpose of the investigations is 1) to observe and record the electromagnetic radiation spectrum resulting from the arcing process, 2) to make estimates of the travel time of the quasineutral plasma cloud based on fluctuations to several Langmuir probes mounted in the ambient plasma, and 3) to study induced arcing between two anodized aluminum structures in close proximity.