Structural changes of surfaces of spacecraft solar array protective glasses being irradiated by 20-keV electrons

When irradiating K-208 and CMG glasses by 20-keV electrons with flux densities of 1010<φe<2×1011cm−2s−1 in vacuum 10−4Pa, electrostatic discharges accompanied by plasma emission and destruction of glass surfaces were observed. Examination of glasses by atomic force microscopy (AFM) showed significant difference in structural changes of surfaces of K-208 and CMG samples irradiated by equal flux densities within the range from 2.0×1010 to 9.0×1010cm−2s−1 that can be explained by different mechanisms of removal of charge accumulated in glasses. Surface discharges generating channels on surfaces of K-208 and CMG glasses appear when φ⩾7.4×1010cm−2s−1 and φ⩾8.7×1010cm−2s−1 respectively. In average, if radiation conditions are the same and φ⩾1.4×1011cm−2s−1, the channels are 1.5 times deeper in K-208 than in CMG.