New results on a point-to-plane DC plasma reactor in low-pressure dried air

Electrical and mass-spectrometric studies of a glow discharge produced by a direct current positive voltage applied to a point-to-plane gap in low-pressure dry air have provided many useful results, which help to clarify the interaction of the underlying physical mechanisms. Systematic studies of this discharge show that electrical parameters and gas pressure influence drastically the cold plasma behaviour. A discharge state similar to that of Townsend is obtained for a restricted region of operation while, outside this region, similarity rules seem not to be fulfilled. The main ions detected during the Townsend-like discharge are O 2 + and NO + while, after breakdown, dissociation products such as O + and N + as well as N 2 + ions are detected. It has been found that ion detection depends strongly upon cathode dark space structure.