Evaporation Rate Affected by Current Density and Number of Vacuum Arc Cathode Spot

Abstract

A remarkable characteristic of a vacuum arc cathode spot, which can remove an oxide layer, is that it moves across the metal surface. However, the influence of current change to the parameter of the cathode spot on the boundary layer remains unclear. This study elucidated the split process and frequency in order to know the removal process of vacuum arc cathode spot with vapor from oxide layer. Experiments were conducted using an SS400 cathode and a cylindrical copper anode. A high-speed video camera recorded the cathode spot movement with ND (Neutral Density) filter. The obtained images were then analyzed using plasma image processing. As described herein, the number of cathode spots, split frequency, evaporation rate on the surface of boundary layer were measured with changing the current. As a result, the parameter of the cathode spot was normalized by the current density and number. In addition, the cathode spot have appropriate number and area for current continuity. In the case of mean number, the current density becomes the maximum. Moreover, the evaporation rate of oxide layer depends on the current density multiplied by number of cathode spot. However, the evaporation rate does not increase because the current per a cathode spot is very small when the number of cathode spots exceeds the mean number.