Composition of a surface flashover plasma

Summary form only given, as follows. The composition of the plasma 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 composed of alumina primarily. The inner and outer conductors are made of tungsten and carbon steel, respectively. Plasma drift velocity components of 2 to 15 cm/μs were measured using two Faraday cup probes. A small portion of the plasma was analyzed by accelerating the ions with a -3000-V, 100-ns square pulse into a 1.9-m drift section with an electron multiplier at its end. Ions that are present on a regular basis are H⁺, O⁺ to O⁶⁺ Al⁺ to Al⁶⁺, and C⁺. Observed occasionally are Fe⁴⁺ and Fe⁵⁺. Detectable levels of tungsten are recorded very rarely. The more highly ionized species are present early in the plasma pulse, and a progressive shift toward the lower ionization states is observed in the later portions of the plasma