Theory of the cathode sheath in a vacuum arc

A previous theory of the plasma sheath transition starting from the charge exchange model for ion collisions is extended to account for ionization and recombination. It is applied to the quasi-neutral boundary layer (presheath) in front of the cathode sheath of a vacuum arc. An essential potential and density difference between the sheath edge and cathodic plasma ball is found. This difference is accounted for in a unified theory of the arc cathode based on G. Ecker's (1971) existence diagram method, which indicates possible areas of arc operation in the T/sub c/j plane, where T/sub c/ is the spot temperature and j is the current density. A numerical evaluation for Cu gives the results which are qualitatively similar to Ecker's theory. The existence areas are quantitatively enlarged and shifted to lower current densities.<
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