Charge Accumulation Characteristics in Proton Beam Irradiated Polymers

The purpose of our research work is to measure the space charge distribution in proton beam irradiated dielectric materials used for spacecraft. Spacecrafts sometimes have a serious damage due to the electro-static discharge accident. It is said that the charge accumulation in dielectric materials irradiated by high energy particles in space environment causes the discharge accident. Therefore, we need to measure the charge distribution in the bulk of dielectric materials. We have been developing a system for measuring internal charge distribution in dielectric materials using pulsed electro-acoustic (PEA) method. Using the system, we tried to measure the charge distribution after proton beam irradiated polyimide (PI) and Tetrafluoroethylene hexafluoropropylene copolymer, Fluorinated ethylene propylene copolymer (FEP) films which have been used as a thermal control layers or an optical solar reflector of the spacecraft. From the result, it is found that positive charges accumulate in bulk of PI and FEP films after irradiation of the proton beams. However, the amounts of accumulated positive charge in PI increase with increase of irradiation time, while those in FEP not increase. Therefore, it is found that the charge accumulation properties strongly depend on the kinds of irradiation materials.