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 μs. These results can be explained by a model based on vapor expansion from cathode spot craters.