Prebreakdown Processes Associated with Surface Flashover of Solid Insulators in Vacuum

A computer simulation of the insulator surface charging in vacuum under the application of a high voltage, is presented for alumina (A1203) insulator and for alumina insulators coated with cuprous oxide (Cu2O) and chromium oxide (Cr2O3). It is shown that the mode of surface charge distribution is dependent on the secondary emission yield of the insulator surface. Mleasurements of insulator- electrode junction fields, using an electronic microforce balance, show the effect of surface coatings on the cathode and anode junction fields. High speed streak photography showing the time development of an arc in the case of coated insulators is presented. The experimental results support the insulator surface charging model which is simulated on a digital computer.