High-current vacuum arc column motion on rail electrodes

Experimental observations were made of the motion of the arc column sustained between Cu electrodes in a vacuum ambient when driven with currents of 1.5-35 kA. Arc-column velocities in the positive Amperian direction of (0.1-3.5) ×10³ m/s were observed in a self-magnetic-field of approximately 50 G/kA with currents of 2-8 kA. The arc motion was observed to be erratic when a dc uniform external field of 450 G was superimposed on the self-field. When the arc was trapped between the self-field and an external nonuniform dc field, the arc located itself such that the net magnetic force upon it was zero. When the self-field exceeded the maximum external field, a transition from a constricted to a diffuse discharge was observed.