Model of surface flashover of insulator in vacuum

Model of surface flashover based on the assumption that discharge develops in a layer of gas desorbed from the insulator surface is proposed. The conditions of avalanche-type increasing of current and of gas density near the insulator surface are analyzed. The surface charge, which appears when the insulator is subjected to high voltages, is taken into consideration. According to the model, surface flashover occurs when the ionization multiplication coefficient, determined by electrons emitted from a cathode junction, exceeds critical size. A necessary condition of flashover is the appearance of a powerful electron emission source at the cathode-insulator junction. The proposed model allows calculation of the flashover voltage and other flashover characteristics of insulators which have considerable value of electron emission yield (e.g. Al₂O₃ ceramic)