Secondary electron emission and surface charging from alumina at high temperature

Electrical breakdown is one of the most serious problems for developing compact and/or higher-voltage insulation in a vacuum. High secondary electron emission (SEE) yields result in the multipactor effect (electron multiplication on the dielectric surface). Multipactor induces not only discharging, but also excess surface heating, leading to localized surface melting. Thus, SEE at high temperature is important for understanding the actual breakdown process. The SEE yields of sapphire were measured at high temperature by a single-pulsed beam method with a scanning electron microscope (SEM) so as to avoid surface charging. In general, the effective SEE decreases by multipactor due to surface charging. Since the electrical conductivity becomes higher at a high temperature, effective SEE can be larger due to less surface charging. In order to estimate the surface charging, multi-pulse beams were injected to sapphire disks at room and high temperature.