Flashover Voltage over Ceramics in High Vacuum

Changes of flashover voltage over various ceramics were investigated in high vacuum with repeatedly applied DC and impulse voltages. It was found that the flashover voltage vs the number of repeated stressing curve showed a peak. The increase in the flashover voltage might be attributed to degassing of the surface of the ceramics, and the decrease might be due to the deterioration of the surface. This tendency was observed in most ceramics, but was particularly noticable in Al2O3 and TiO2.