Ceramic secondary electron emission and surface charge measurements

The secondary electron emission (SEE) coefficient is strongly dependent on material type due to the fact that secondary electrons come primarily from inelastic electron collisions and intrinsic lattice losses. Other macroscopic factors affecting the emission process are related to surface finish, surface coatings, ion implantation, and surface preparation and cleaning procedures. SEE plays a key role in most proposed models for insulator surface flashover development. We have measured total surface electron yield from a number of materials as well as from similar materials with different surface treatments. The experiments were performed using both a continuous wave and a pulsed electron gun with a hemispherical electron energy spectrometer at vacuum levels in the range of 10^-8 torr. Electron spectroscopy reveals substantial difference in total electron yield due to minor changes in surface finish. The results of SEE measurements and the secondary electron energy distribution, using both continuous wave and pulsed electron beams, are presented. Quasimetalized surfaces show distinct SEE reduction over nontreated samples. Another measurement taken, characterized insulator surface charge as a function of pulse length, number of pulses, and total electron beam current. Material surface charge characteristics using electron pulses from 100 μs and up to 1 ms are presented. Results indicate radically different surface charge behavior between single pulse, repetitive pulse, and continuous wave experiments.