Dielectric characteristic evaluation of proton beam irradiated polyimide films

We evaluate the dielectric characteristic of polymeric materials for MLI (Multi Layer Insulator, a kind of thermal insulation material) for spacecraft under high energy proton irradiation using results of space charge distribution. Spacecrafts have a serious damage due to the electro-static discharge accident. The electric charges are accumulated in the polymeric materials due to radioactive rays, especially electrons and protons. The charge accumulation is the origin of aging and discharging phenomena, furthermore those become trigger for spacecraft operation anomaly. Therefore, we need to obtain the space charge distribution in the bulks. In this study, we especially focused polyimide films for MLI irradiated by high energy proton. We measured the space charge distribution in the bulks during and after proton beam irradiation. From the results, it is found that positive charges accumulate in the bulk at the position of proton penetration depth. Furthermore, the characteristics of space charge accumulation are difference between the current and energy of irradiated proton. In case of comparison between high and low dose rate irradiation under same total dose condition of both irradiation, the mobility of accumulated charges increase with rate increment. We also obtained same tendency from the results of conductivity measurement treated by ASTM method. From the above our descriptions, we discuss and estimate the aging of dielectric properties on the polyimide films irradiated by proton in this paper.