Investigations of Fast Insulator Surface Flashover in Vacuum

Electrooptical measurements of the electric fields along insulator surfaces have been made, utilizing the Kerr and Pockels effects, to determine the mechanisms associated with fast insulator flashover in vacuum. Data are presented that show the temporal and spatial variations of the surface fields prior to and at flashover for insulator surfaces oriented at 0° and 45° with respect to the applied field. It is found that the surface field near the cathode is enhanced and the field near the anode is reduced during the excitation. The results further show a temporal reduction in the field nonuniformity as flashover is approached. The field collapse associated with flashover occurs very rapidly for 0° surfaces. The field collapse for 45° surfaces begins at the anode and propagates at 0.83 cm/ns towards the cathode. Mechanisms consistent with these experimental measurements are postulated.