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Study on the vacuum surface flashover chararteristic of polyimide at cryogenic temperature

Insulation system is a critical part of large superconducting equipment, and for the particular operating environment the insulating materials utilized under cryogenic temperature need to be studied. In this study, vacuum flashover characteristics of polyimide film under temperature form 25K to 300K was studied by using the self-developed cryogenic temperature dielectric test system. The results show that the surface flashover voltage rises as the flashover times increasing and approach to a stationary value under any conditions. However, the initial flashover voltage and the stable flashover voltage decrease by 2–3 kV when weak light exits which may be affected by photons. On weak light and dark conditions, temperature has little influence on the initial flashover voltage, and for the stable flashover voltage, it remains stable under 25–200 K, and drops slightly with temperature increasing from 225K to 250K, and then rises modestly under higher temperatures, but still lower than that of 25–200K, which may results from the temperature change and the absorbed gas on the surface of polyimide film.