The time interval from voltage application to the arc occurrence in the impulse discharge process of a positive point to plane configuration having a protrusion on the plane was measured in air at low pressure. The time was compared with one in the configuration without protrusion under the same conditions. Simultaneously with the measurements of the time, the luminous phenomena of the discharge processes were examined by an image converter camera and a still camera.
Furthermore, before and after the frequent discharges, the surface condition of the protrusion exposed to the impulse discharges was observed by an electron probe microanalyser, and the binding energy of Cu-2p3/2 at the protrusion surface was investigated by means of a x-ray photoelectron spectroscope.
The main results are as follows: (1) The time till arc occurrence in the configuration with protrusion as compared with one in the configuration without protrusion is larger for low applied voltages and smaller for high applied voltages. (2) As the number of times of the discharge is increased, the time till arc occurrence is later and finally both of the time and the length of the discharge channel become roughly constant. (3) The surfaces of protrusion and plane are oxidized by frequent impulse discharges. Consequently, the change of cathode spot position occurs.
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