抄録
Surface flashover on the alumina ceramics is one of the most serious problems for developing the dielectric insulation. The flashover takes place by (1) multipactor, electron multiplication on the surface and/or (2) discharge of the accumulated charges (due to multipactor). Since the multipactor sometimes induces localized surface melting, surface charging is evaluated not only at room but also at high temperature. The alumina ceramics with higher purity show lower surface chargings at room temperature and non-chargings at 650°C. A sapphire (single crystal alumina) disk shows high surface charging even at 650°C. Considering the poor performance of the sapphire for the rf window usage, less charging materials at high temperature is indicated to be the promising candidates for the dielectric insulation.
