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The three stages of anode surface area evolution in an industrial CO2 laser owing to the formation of oxide films have been recognized. The increase of the current at which the glow-to-arc transition occurs by transition to the final (homogeneous) stage has been established. The disappearance of the anode current spot under presence of the homogeneous low-conducting coating on the anode surface has been shown using 2D simulation. The performed studies enable one to highlight the dominant role of the surface state in anode spot formation in an elevated pressure glow discharge.

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 0 :and NO+ while, after breakdown, dissociation products such as O+ and N+ as well as N : ions are detected. It has been found that ion detection depends strongly upon cathode dark space structure.

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