Effects of Irradiation on Surface Charge and Discharge Behaviors of PI Film Under Pulse Voltage

The superconducting magnet, as a main component of the international thermonuclear experimental reactor (ITER), is critical to the ITER's long-term stability. Polyimide (PI) not only has excellent electrical properties at cryogenic temperature, but also has strong irradiation resistance, which has become the common choice of insulating materials for the superconducting magnet. Due to the pulsed power supply used in the ITER, PI is facing the dual challenges of cryogenic temperature and pulsed voltage. The surface charge characteristics of irradiated PI film by different doses of electron beam were studied in this paper. The surface charging is completed under the pulse voltage with 40% relative humidity. The partial discharge initial voltage (PDIV) and breakdown voltage in liquid nitrogen (LN ₂ ) were measured by electrostatic voltmeter. The findings indicate that proper irradiation can help to minimize charge accumulation and decrease the trap level. At the same time, the PDIV and breakdown voltage can be increased by irradiation. However, too much irradiation can weaken this influence.