Cathode spot motion in high current vacuum arcs on copper electrodes

Abstract

The motion of vacuum arc cathode spots under the influence of the self-generated magnetic field has been investigated for copper electrodes at currents up to 6.9 kA. The spots were photographed with a high-speed framing camera. The magnetic flux density was measured. Surface contamination caused large changes in spot velocity. For velocities up to 15 ms -1 and corresponding flux densities up to 2*10 -2 T the velocity is proportional to the flux density. Above 20 ms -1 and 4*10 -2 T the velocity increases relatively slowly with increasing flux density. Velocities of more than 30 ms -1 were not observed.