The relationship between charge decay process and current density differential on polyimide and fluoride films irradiated by electron

Spacecraft are sometimes seriously damaged by electrostatic discharge in polymeric materials. Various polymeric materials are used for the surface materials of spacecraft, such as a MultiLayer Insulator (MLI) or an Optical Solar Reflector (OSR). They are charged up by irradiation of solar particles and high-energy charged particles, particularly those such as charged particles like electrons and protons. The accumulations of the charges are the origin of discharge phenomena, and they become a trigger for some anomalies of spacecraft operation or a degradation of the materials. Therefore, it is necessary to investigate the charging effect on the dielectric properties of these materials. Since the dielectric properties like electrical conductivity have a strong correlation with the charge accumulation in the bulk, we especially focused on the space charge behavior in electron beam irradiated dielectric materials, especially in polyimide film used as MLI and fluoride films used for OSR and wire harness. To observe the space charge accumulation processes in polyimide films and fluoride films with and without electron beam irradiation, the pulsed electro-acoustic (PEA) measurement were carried out after irradiation for dozens of days. Furthermore, the conduction current in them were also measured according to the American Society for Testing and Material (ASTM) method (IEC has also same standard). On the basis of the results, we confirm that the charge decay behavior is different between polyimide film and fluoride films. The current density decreased on irradiated polyimide compared with non-irradiated film. This phenomena also was confirmed by the space charge measurement results that was large amount of accumulated charge still remained in the bulk during several hours. On the other hand, the current density of irradiated fluoride films approximately 100 times larger than non-irradiated film. From the results, it is considered that the increasing of current density on fluoride films may influence the charge accumulation in the bulk.