Theoretical and experimental studies on internal charging/discharging phenomena occurring spacecraft material

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In order to simulate the space radiation environment, the high vacuum chamber (2002) and the electron gun (2003) were installed. Electron irradiation tests on several dielectric materials such as Kapton and Teflon were carried out and the charge distributions inside the materials were obtained using the measurement technique previously developed by the present research group. Tests on glass material used for the cover glass on solar panels were also carried out. The results indicate that there exists a peak of charge density inside the dielectric material and high electric field and electric potential are induced due to the electron irradiation. The penetration depth of the charge becomes deeper as the incident electron energy increases. The charge density profiles inside glass materials vary according to the composition, but clear relationship between the profile and the component has not been revealed. The internal charging database is going to be organized using the data obtained. As for theoretical point of view, the physical model for collision between incoming electrons and atoms consisting the dielectric material was constructed based on consideration of the quantum theory. Numerical simulations based on the model were carried out using the Monte-Carlo methodology. Each electron injected onto the material surface is tracked based on the statistical estimations, and the trapped electrons are counted to construct charge density distribution. A PC-based parallel computer was installed in 2002 to execute this calculation because this type of simulation requires huge memories and high CPU performance. The simulation results show the electron accumulation process, but quantitative agreement of charge profile compared to that obtained by the experiments were not obtained. The detailed investigation clarified that the excessive ionization occurred among the collision processes and thus the positive charge near the irradiated surface were observed.