Kerr electro-optic field mapping measurements in electron-beam irradiated polymethylmethacrylate

To understand electron-caused discharges along insulating solid surfaces on spacecraft as well as in solids, Kerr electro-optic field mapping measurements have been performed in electron-beam-irradiated polymethylmethacrylate. The accumulated trapped charge results in large self-electric fields of the order of 1 to 3.5 MV/cm. Measurements were done at electron-beam energies up to 2.6 MeV at low (20 nA/cm/sup 2/) and high (300 nA/cm/sup 2/) current densities and for sample thickness of 0.635, 0.95, 1.27 and 2.54 cm. It was found that volume breakdown through the electron charged region may occur spontaneously when accumulated charge levels are high. Typically at breakdown the net charge density magnitude exceeded 1 mu C/cm/sup 2/ and internal fields exceeded 1.8 MV/cm. Charge dynamics during electron-beam irradiation was also analyzed on the basis of a simple model consisting of the continuity and Poisson's equations including charge generation and radiation-induced conductivity.<
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