Arcing on aluminum anodized plates immersed in low-density plasmas

A number of experiments have been done to study characteristics of the plasma contamination and electromagnetic radiation generated by arcing on anodized aluminum plates immersed in low-density plasma. The low-Earth-orbit plasma environment was simulated in a plasma vacuum chamber, where the parameters could be controlled precisely. Diagnostic equipment included two antennas, a mass spectrometer, a spherical langmuir probe, a wire probe, and a very 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 200 MHz, We found that the level of interference considerably exceeds the limitations on the level of electromagnetic noise set by technical requirements on Space Shuttle operation, Experiments with two independently biased plates have shown that the arcing onset on one plate generates a pulse of current on the second plate and that the secondary current pulse has a significant 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 significant degradation of the coating layer was determined by measurement of the resistance of the plate, which had experienced a few hundred arcs.