Mass spectrometry of a fast plasma jet

Abstract

The composition of the plasma jet used as an electron source for the Plasma Edge Cathode experiment has been determined. A time of flight spectrometer was constructed for this purpose. The plasma is produced by the surface flashover of a coaxially arranged dielectric. The plasma drift velocity was measured by the use of Faraday cup probes. A small portion of the plasma is analyzed by accelerating the ions with a pulsed electric field into a drift section with an electron multiplier at its end. The time delay between the creation of the plasma and the accelerating pulse is adjustable, allowing analysis of the entire plasma pulse. Oxygen, aluminum, iron, carbon, tungsten and hydrogen have all been detected in the plasma jet. The most abundant of these elements is oxygen, followed by aluminum. Both were present in every sample analyzed. Iron and carbon, on the other hand, are only found in certain portions of the plasma; iron in the earlier part of the jet and carbon in the very late part. Tungsten was present only one time in sufficient quantity to be detected. Hydrogen ions appear in the very early portion of the plasma, and their abundance increases with the time between discharges. The more highly ionized species are present in the fast part of the plasma jet, and a shift toward the lower ionization states is observed in the slower portions of the plasma.