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Theory and modelling of arc cathodes

Understanding of cathode phenomena in arc discharges has considerably improved in recent years due to the progress both in experiment and in theory. A review of the present understanding of cathode phenomena in high-pressure arc discharges is given. The effect of processes in the arc column on the cathode part of the discharge in most cases is weak, which is a consequence of the fact that the energy flux coming to the cathode is formed in a thin near-cathode plasma region. A theoretical model of the near-cathode region is described. The model can be used both by itself or as a part of a code modelling the whole system of arc electrodes. In particular, the model results in a simple estimate of the upper limit of the cathode temperature and of the lower limit of the temperature inside a cathode spot. A simple asymptotic solution to the thermal conduction equation in the cathode body, describing a steady-state cathode spot, may be obtained making use of the fact that the energy flux from the plasma to the cathode surface is localized in a narrow temperature range. Approaches to a self-consistent modelling of diffuse and spot modes of current transfer to the cathode are discussed.