Measurement of the Copper Vapor Density in a Magnetically Stabilized High-current Vacuum Arc by the Laser Absorption Method

The high-current interruption ability of the vacuum interrupter depends on the state of the residual plasma remaining between electrodes after an current zero. In this study, the copper vapor density around the current zero with a half-period of 1 ms and a peak current of 3 kA arc was measured using the laser absorption method. The copper vapor density found to be 8×1017 m-3 at current zero and was found to be independent of current zero gradients and arc current peak. After current zero, the copper vapor density decayed with a time constant of approximately 400 μs. The decay time observation by LIF signal agreed well with that of the absorption method. This decay time of the copper vapor density can be explained based on the calculation of the cooling characteristics of the cathode spot crater which supplies copper vapor.