A model for the cathode mechanism in low-current metal vapour arcs

Abstract

An analytical model is proposed for the cathode spot of a metal vapour arc. A number of physical parameters at the cathode surface and at the boundary of the cathodic plasma such as macroscopic velocity, temperatures, fluxes, particle densities and electric field can be determined from equations for conservation of electric charge, mass, momentum and energy, the equation for ion current to the cathode, bipolar space charge equation, Saha equation, electron emission equation, and evaporation equation. The cathode drop voltage and the current density serve as independent variables. The multiply charged ions are taken into account, and the jumps of some quantities over the first mean free path-due to non-equilibrium evaporation-are incorporated into the model. Numerical calculations are carried out for low-current copper vacuum arcs. The results are compared with experimental data.