The mechanism of surface charge accumulation on alumina ceramics under impulse voltage in vacuum

Surface flashover across solid insulators in vacuum-dielectric system greatly weakens the overall performance of pulsed power equipment. It is reported that flashover is crucial in relation to surface charging behaviors on insulator surface. Therefore, it is of great significance to study mechanism of surface charge accumulation in vacuum. In this paper, surface charging behaviors on alumina ceramics insulators were experimentally investigated under negative impulse voltage. Surface potential distribution were measured by an electrostatic voltmeter with a vibrating Kelvin probe utilizing field nullifying technique. Surface charging behaviors for different amplitudes and number of negative impulse voltage were both studied, and the metal granule was introduced to research the development of surface charge accumulation. For impulse voltage, Schottky injection of homo-charges from electrode into sample surface layer has little influence on surface charging as the voltage duration is too short for charge injection and migration on surface layer. Surface charging is mainly caused by the secondary electron emission (SEE) process on sample surface due to its extremely fast establishment process. The insulator surface is merely positively charged. Surface charges gradually expand from cathode toward anode with the application of impulses, which needs ∼10 impulses to reach a saturated charged surface. A linear relationship is obtained between saturated surface potential and applied voltage.