Charge accumulation phenomena in PI film irradiated by a proton

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 the results of space charge distribution and current measurement. Spacecraft have a serious damage due to the electrostatic discharge accident. The electric charges are accumulated in the polymeric materials due to radioactive rays, especially electrons and protons. Those charges become the origin of aging and discharging phenomena. Furthermore, those charging and discharging phenomena becomes a trigger for spacecraft operation anomaly. Therefore, we need to obtain the electric property. From the above reason, we have studied space charge accumulation phenomena in the dielectric bulks using PEA method. In this study, we especially focused polyimide (PI) films for MLI irradiated by high energy proton. While many researchers have studied to discuss the charging phenomena in several dielectric materials irradiated by e-beam with several energies, the charging characteristic in those materials irradiated by proton was not treated. Therefore, we especially focused on an internal charging phenomena in polymeric materials irradiated by a proton. From the results, it is found that positive charges accumulate in the bulk at the position of proton penetration depth. We also have tendency that accumulated charges decreased during the irradiation depended on irradiation current density. We thought that the origin of the phenomenon is produced by RIC. Concerning the confirmation of our prediction based on PEA measurement, we also obtained the conductivity in the PI bulks irradiated by proton using ASTM method. From the above our results, we discuss and estimate the dielectric properties of the PI films irradiated by proton in this paper.