On modes of arc cathode operation

A review is given of the different modes of arc cathode operation. Arcs in a pressure range from UHV up to ⩾10⁷ Pa and in a current range from 0.1 A up to 10⁵ A are considered. Glow discharges are briefly mentioned for comparison. Typical conditions, parameters, and a phenomenological description of the different arc cathode modes are presented. Emphasis is put on the main electron emission mechanism. Two groups are distinguished: nonstationary modes that are governed by thermofield emission coupled with explosive processes, and stationary modes that are governed by thermionic emission. It is pointed out that the current density and the erosion rate cover a range of at least nine orders of magnitude, depending on the mode established. In the framework of this classification, it was shown that phenomena that appear to be different, such as the thermionic spot mode at low pressure and the thermionic vapor mode, represent in principle the same mode; only the discharge medium is different. It is either a gas or the electrode vapor, respectively