Laser measurement of copper vapor density after a high-current vacuum arc discharge in an axial magnetic field

The copper vapor density after the occurrence of a magnetically stabilized high-current vacuum arc was measured by the laser absorption method. Measurements were performed in a vacuum triggered gap with oxygen-free, axial magnetic field (AMF) Cu electrodes (40-mm-diameter cathode and 60-mm-diameter anode), separated by a gap of 30 mm. The arc current was a sinusoidal wave having a half-period of approximately 10 ms and a peak value ranging from 3 to 10 kA. The arc was stabilized by a magnetic field produced by the AMF electrodes. The copper vapor density at current zero increased with peak arc current and did not depend on the current zero slope. After current zero, the copper vapor density decayed with a time constant of approximately 400 /spl mu/s. These results can be explained by a model based on vapor expansion from cathode spot craters.

I. Introduction

The high-current interruption of a vacuum interrupter depends on the state of the residual plasma and vapor remaining between the electrodes after the current zero. Metallic vapor in the residual plasma, for example, delays the recovery of dielectric strength, and charged particles in the residual plasma may cause reignition of the arc.