Mechanisms of charging of insulators under irradiation with medium-energy electron beams

The electron emission and charge characteristics of a large number of massive insulators are investigated qualitatively and quantitatively. It is demonstrated that irradiation of insulators with a medium-energy continuous electron beam leads to a decrease in the equilibrium energy of incident electrons (the second critical energy) as compared to the theoretical value. The equilibrium state of charging to saturation is attained for times from several seconds to several hundred seconds depending on the irradiation current density, the electron energy, and the insulator material. The mechanisms of charging are explained in the framework of the model according to which irradiation is accompanied by the formation of a charged double layer that consists of a positively charged layer (with the thickness equal to the escape depth of secondary electrons) and a negatively charged layer (with the thickness equal to the penetration depth of primary electrons).