A treatment which improves surface withstand voltage in vacuum

A treatment which significantly increases the pulsed surface flashover potential of some insulator materials in vacuum is described. The flashover potential is measured by placing a short cylindrical sample between brass electrodes in a vacuum chamber at a pressure of 10^-4 Pa and applying a high-voltage (HV) double exponential pulse with 1.5/135- mu s time constants. The treatment consists of exposing a sample to 80000 sparks from a spark plug in vacuum. For each material, an untreated and a treated sample are measured under identical conditions, and the results compared. Results on Lexan show an increase in flashover potential from 100 to 170 kV. On the machinable ceramic Macor, the results were 60 kV untreated and 140 kV treated. Surface analysis using electron spectroscopy for chemical analysis shows that the treatment alters the surface composition of the material. Also, the secondary electron emission coefficient (SEEC) has been measured for treated and untreated samples over a range of incident electron energies. The SEEC changes dramatically after treatment.