Surface and Internal Charge Measurement in Fluorinated Polymer Irradiated by Electron using Non-contact Type PEA Method

抄録

Spacecraft are exposed by radioactive rays, such as highly energetic electrons, protons, and plasma. The surface insulating materials of spacecraft are charged because of being exposed by such high energy charged particles. This charging phenomenon is one of the origins of an electrostatic discharge and may lead to a fatal error during those operations of spacecraft. For the improvement of the reliability of spacecraft operation, we should understand charge accumulation phenomena based on the actual surface conditions. Therefore, our group and other researchers have tried to develop systems to measure the surface and bulk charges of some seat specimens modeling surface insulators. As the results, we developed new space charge measurement equipment based on the pulsed electroacoustic (PEA) method. That system can apply the pulsed electric filed to the sample through the vacuum gap using a grid electrode located 125 µm above the sample. Electrons through the grid electrode to the sample. Therefore, this electrode can be applied to measurement of the surface and internal charge accumulation in the bulk of sheet specimens. While our past study had described only internal charge accumulation by the conventional PEA method, this paper presents a seamless charge profile from the surface to internal of the sample by such newly developed method. In this paper, we measured space charge distributions caused by electron irradiations to fluorinated materials were studied by using above developed method. The negative charge accumulation distributed the surface and penetrated the bulk up to approximately 32 µm depth from the surface. The amount of irradiated electrons accumulation was more than 30 times as much as the results obtained by a conventional measurement system. From those results, the space charge distribution can be measured under vacuum conditions close to actual situations.