INSULATOR SIZE EFFECT ON ELECTRON-IRRADIATED QUARTZ

A time-resolved current experiment measuring separately the surface an d bulk currents flowing through an insulating sample under electron be am irradiation employing a scanning electron microscope is performed t o investigate charging and flashover phenomena. A set of metallic aper tures of various values of radius are used to vary the area of the ins ulator. It is observed that the bulk current decreases monotonically w ith time until reaching a constant value, while the surface current ex hibits two different trends: decreasing monotonically with time, and d ecreasing with time at first and then increasing. Such observations ar e related to the establishment of a dynamic equilibrium between electr on trapping and detrapping, as well as the flashover behavior, and dep ends on the insulator size and the experimental conditions.