Influence of XLPS Roughness on Surface Flashover Characteristics in Vacuum Under Nanosecond Pulses

Surface flashover in vacuum is a critical factor restricting the stable operation of the high-power pulsed generators. Cross-linked polystyrene (XLPS) is always used to manufacture typical insulators for power pulsed generators, so it is important to study the surface insulation performance of the XLPS in a vacuum to improve the normal operation performance of the device. Based on the vacuum surface flashover test platform consisting of a solid-state gigawatt-level pulse generator and a test cavity, XLPS samples with a thickness of 13 mm were used to investigate the influence of roughness on the surface flashover characteristics. Samples with roughness of 1.3, 1.7, 2.2, and $2.7~\mu $ m were tested under both single and 10 Hz modes. It is found that the surface insulation performance of samples increases first and then decreases with the increase of roughness under both modes. Scanning electron microscope (SEM) was used to observe the micromorphology of the sample surface before and after the surface flashover events, enabling analysis of the effect of micromorphology on electron motion. Comparative analysis of the experimental results reveals that the first vacuum surface flashover voltage under both modes primarily depends on the surface roughness. Meanwhile, under 10 Hz mode, the first 50% flashover voltage, the conditioned flashover voltage, and the hold-on voltage are higher than those obtained in single mode, which indicates that the loading condition of the repetition rate pulse has a good aging effect on the sample.