Effect of Material Parameters on the Charging Characteristics of Irradiated Dielectrics

In order to accurately predict the charging characteristics of dielectric materials used on spacecraft surfaces, a knowledge of material parameters determined under irradiation conditions is required. The relative importance of these parameters can then be determined by comparison with numerical models. This paper reports the measurements of the charging characteristics and material parameters of Teflon, Kapton and fused silica samples irradiated by a monoenergetic electron beam and the comparison of these measurements with the predictions of a numerical model. The experimental system is configured to closely approximate the one dimensional geometry of the numerical model. Time dependent surface potentials are inferred from the measurement of the energy spectra of secondary electrons emitted during irradiation. Bulk conductivities are inferred from equilibrium surface potentials and equilibrium substrate currents. The measured secondary electron emission coefficients for Teflon and Kapton are in agreement with values in the literature as is the bulk conductivity of Teflon. The conductivity of Kapton is observed to be larger than values reported in the literature and has an energy flux dependence. Comparisons with the numerical model predictions indicate that secondary electron emission is the controlling material characteristic for Teflon and fused silica whereas the secondary emission and bulk conductivity are the controlling factors for Kapton.