Erosion rate and voltage distribution in contracted (with cathode spot) and diffuse (spotless) low-current vacuum arcs

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Abstract
The influence of ambient gas pressure and emission current on the potential distribution in a diffuse arc has been studied. The conditions determining the formation of the potential 'hump' near the cathode have been determined. The erosion rate Upsilon approximately=10-3 g C-1 for an individual crater (local erosion rate) has been measured for a contracted vacuum arc. In both types of arc the local erosion rate is well in excess of the erosion rate measured by the weighing method. The conclusion is drawn that most of the evaporated atoms ( approximately= 90%) have to return to the cathode. The diffuse and the contracted vacuum arcs reveal common properties despite a great difference in the current density. The idea of the potential hump can unite both types of arc and explain their characteristics.