Arcing on aluminum anodized plates immersed in low-density plasmas

A number of experiments have been done to study characteristics of the plas ma contamination and electromagnetic radiation generated by arcing on anodi zed aluminum plates immersed in low-density plasma. The low-Earth-orbit pla sma environment was simulated in a plasma vacuum chamber, where the paramet ers could be controlled precisely. Diagnostic equipment included two antenn as, a mass spectrometer, a spherical langmuir probe, a wire probe, and a ve ry sensitive current probe to measure are current. All data except for mass spectrometry were obtained in digital form with a sampling interval of 2.5 ns that allowed us to study the radiation spectrum at frequencies up to 20 0 MHz, We found that the level of interference considerably exceeds the lim itations on the level of electromagnetic noise set by technical requirement s on Space Shuttle operation, Experiments with two independently biased pla tes have shown that the arcing onset on one plate generates a pulse of curr ent on the second plate and that the secondary current pulse has a signific ant amplitude. The sampling interval for mass spectrometry was 250 ms. This allow ed us to obtain the rate of plasma contamination due to arcing. A si gnificant degradation of the coating layer was determined by measurement of the resistance of the plate, which had experienced a few hundred arcs.