Observation of tungsten particles in vacuum arcs by laser induced fluorescence

The authors have clarified the relation between the decay of tungsten ion density in the vicinity of current zero and vacuum arc mode by using LIF method and a high speed video camera in tungsten vacuum arc of 60 Hz sinusoidal current with the peak value of 3.3, 6.7 and 9.8 kA. The tungsten ion density before current zero decreased as the current decreased. In the case of 6.7 kA, the transition to the anode spot mode occurred and an arc column was observed. The density near the anode before current zero was higher than near the cathode and the density near the anode was about 10 times as high as the case of 3.3 kA which was diffuse mode. In the case of 9.8 kA, the density near the anode was not significantly different from 6.7 kA. But the density near the cathode was higher than near the anode and the eruption from the cathode was observed by a high speed video camera. They concluded the arc at 9.8 kA was the intense arc mode. And the density at current zero was higher than the other case and tungsten ion was observed until about 30 μs after current zero