Non Steady Cathode Spot Operation at a Microprotrusion in a Vacuum Arc

A physical model and non steady system of equations was suggested in order to describe the cathode spot evolution at the single protrusion. The model considers the self-consistent phenomena including the protrusion heating, kinetics of cathode vaporization, plasma generation and current continuity. The time dependencies of spot current, current density, plasma parameters and protrusion geometry were calculated. It was shown that the spot life-time is restricted by the protrusion disappearance due to cathode erosion. Furthermore, spot operation in the cathode body (after protrusion disappearing) cannot continue due to the sharp energy growth by the body heat conduction, which cannot be supported in the low voltage vacuum arc mode. It was found that 1-5 micrometer protrusions reduce their size to zero with time 0.5-10 microseconds respectively