Hiroyuki Sasao

Investigation of ion behavior associated with anode-spot mode transition in vacuum arcs

The ion behavior phenomenon associated with transitions of the anode discharge mode to the anode-spot mode is studied by measuring the wall ion current and by spectroscopic observation in vacuum arcs. The anode mode transfers when the wall ion current attains a certain magnitude that is independent of the cathode, but dependent on the anode. The ion-current function to the arc current increases when the arc current increases in the diffuse arc. Spectral-line intensity of Cu III emitted from the plasma in the anode region increases with an instantaneous arc current of a 5-kA peak (kAp) sinusoidal half-wave. These findings suggest an idea for the mode transition, that an ion generation region appears, and that an increase in the ion density produces a positive potential hump near the anode, which results in the negative anode voltage drop triggering the mode transition. After the mode transition, an arc current is found to reduce the ion current near the crest of a sinusoidal current in a copper arc. This appears to be significant for the arc on a small anode. The decrease in the ion current is attributed to the recombination of ions decelerated by anode vapor with electrons emitted from the hot spot on the anode. >

Self-extraction of negatively charged carriers from anodic vacuum arcs

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