Search

We have clarified the relation between the decay of tungsten ion density in the vicinity of current zero and vacuum arc mode in high current period by using a laser induced fluorescence method in tungsten vacuum arcs of 60 Hz sinusoidal current with the peak value of 3.3, 6.7, and 9.8 kA. In the case of 6.7 kA, the arc mode was the anode spot mode. Because of the generation of the anode spot, the tungsten ion density near the anode was higher than near the cathode and the density near the anode was about ten times as high as the case of 3.3 kA which was the diffuse mode. In the case of 9.8 kA, which was the intense arc mode, the density near the anode was not significantly different from the case of 6.7 kA. But the density near the cathode was higher than near the anode. And tungsten ions were observed till about 30 [[micro]seconds] after current zero while they disappeared at current zero in the other cases.

The density distribution and the velocity of copper neutral atoms emitted from a single cathode spot in 40 A vacuum arc were measured by the two-dimensional (2-D) laser-induced fluorescence method. The density was calibrated from the two-dimensional fluorescence image observed by a CCD camera. The gap space was almost filled with the copper atoms, and the density reached 5 x [10.sup.19]/[m.sup.3]. We varied the wavelength of the laser light and measured the velocity of the copper atoms emitted from the cathode spot using the effect of Doppler shift. The velocity of the copper atoms was about 10 km/s. Index Terms - Cathode spot, laser-induced flourescence, vacuum arcs.

Measurement and magnetic analysis of self-extracted negatively charged carriers (NCC) from anodic vacuum arcs are presented. They flowed to charge collectors made of stainless-steel which were electrically connected to a cathode. When a 60 Hz sinusoidal arc current of 40 kA was burned on 20 mm dia. copper electrodes spaced 4 mm apart, a negative current of approximately 900 A (which corresponds to the NCC's flow of 1.8 C) flowed to a cylindrical collector surrounding the arc. The floating collector potential relative to the cathode was measured, and the mean energy of NCC was estimated to be greater than 40 eV. It was difficult for the NCC to flow from anodic vacuum arcs when an anode was made of zinc or cadmium, of which atoms have electron affinities of less than 0 eV. A magnetic filter of about 500 G, which was placed between the arc and a 30 mm dia. circular collector, does not effect the NCC's flow from a 4 kA arc burned on copper electrodes. It was possible to extract a large amount of negative copper ions from the anodic copper vacuum arcs.