Two-Dimensional Observation of Single Cathode Spot Copper Vapor in Vacuum Arcs by Laser-Induced Fluorescence

Abstract

Vacuum arc cathode spots are centers of metal vapor evaporation, electron emission and plasma production. Arc properties are dominated by the behavior of the cathode spots. A systematic investigation on the density of copper metal vapor emitted from a single cathode spot is benefit for understanding the mechanism of vacuum arc discharge. The objective of this paper is to get the spatial density distribution of copper neutral atoms emitted from a single cathode spot in ~55A vacuum arc by planar Laser Induced Fluorescence (LIF) method. The experiments are conducted with CuCr10 (Cr weight of 10%) butt contacts in a demountable vacuum chamber. 2D distribution of copper metal vapor density is photographed by an intensified CCD cameral (i-CCD) with an exposure time of 50 ns. The uniform constant Axial Magnetic Field (AMF) within the inter-contacts region is supplied by Helmholtz coils. 2D copper vapor density distribution between two electrodes as well as the influence of external AMF on vapor density distribution are investigated. When the arc current is ~55 A, a typical cathode spot or two spots are observed in the experiments. Copper vapor density reaches the maximum value 6×1019 m-3 in the center of cathode spot.