The vacuum arc cathode spot and plasma jet: Physical model and mathematical description

A physical model of the cathode processes and flow of material eroded from the cathode of a vacuum arc is formulated. The model considers the plasma jet and the plasma generation regions, and provides electrical current continuity at the metal-plasma boundary in the cathode spot. Based on an analysis of the kinetics of cathodic evaporation and plasma flow in the hydrodynamic region, a closed system of equations is obtained. Boundary conditions for the cathodic plasma expansion are formulated. The system of equations allows to compute the spot parameters (cathode potential drop, cathode material erosion rate, plasma parameters -velocity, density, temperature, e.t.c) using a self-consistent description of the plasma flow in the cathode spot and cathode jet regions. The calculations for spot currents 1 - 20 A show that the cathode potential drop increases, erosion rate decreases with spot current and spot life time decreasing.