Investigation of Space Charge Accumulation Behavior by Repeated Proton Irradiation

There are many high-energy charged particles in space, and when spacecraft surface insulating materials are exposed to this environment, they become charged inside the insulating materials, causing electrical discharges. In fact, since ESD (electrostatic discharge) caused by charged particle irradiation accounts for most spacecraft operational anomalies, it is important to understand the charging characteristics of insulating materials from the perspective of stable spacecraft operation. Currently, surface potential measurement is generally used to evaluate the charged properties of insulating materials by charged particle irradiation. However, when insulating materials are irradiated with high-energy charged particles, they penetrate and are charged inside the insulating materials, so internal charging measurement is essential to understand the charging mechanism. While previous studies on the charged properties of insulating materials have focused on the effects of electron irradiation, there are still few studies on the insulating properties of spacecraft surface materials irradiated by proton beams. In view of the above, it is very important to understand the charging and discharging phenomena caused by proton irradiation of insulating materials. In this study, fluorine-based insulating material (FEP) used in Optical Solar Reflector (OSR) of spacecraft was taken up to investigate the charge accumulation characteristics by proton irradiation. Using an irradiation-type PEA apparatus based on the Pulsed Electro-Acoustic (PEA) method, which is a proven space charge measurement method, we measured the space charge accumulation characteristics of samples under proton beam irradiation. In the previous study, as an investigation of space charge accumulation behavior by irradiation flux, the irradiation fluence was unified, and the space charge distribution inside the insulating material was measured for proton irradiation at each irradiation flux and irradiation time. The problem was that the time required to irradiate a sample at one time was limited due to the machine time of the accelerator. Therefore, repeated irradiation was investigated as a method to extend the irradiation time. The charge accumulation behavior of insulating materials that have been irradiated with protons and then re-irradiated with protons was investigated by spatial charge distribution measurements. The irradiation conditions were 2 MeV acceleration energy and 60 nA/cm
²
irradiation flux. One hour after 15 minutes of irradiation, the same irradiation conditions were applied again for 15 minutes. Measurements were taken at 5-second intervals for a total of 30 minutes, 15 minutes during irradiation and 15 minutes after irradiation. As a result, continuity was observed in the charge accumulation behavior at the end of the first irradiation and at the time of the second irradiation. This suggests that the irradiation effect of the first irradiation may have remained at the second stage of irradiation, this suggests that the irradiation effect of the first irradiation may have remained at the second stage of irradiation, and it is suggested that repeated irradiation may enable us to obtain the charge accumulation behavior of longer irradiation time.