Charge transport and yield variations in electron-beam irradiated insulators

In this paper the space-time evolution of free and trapped charge densities and the variations of the secondary electron yield in electron-beam irradiated insulators are investigated with the help of a self-consistent drift-diffusion-reaction model. It is shown that focused high-current low-energy beams create quasi-stationary shock-type distributions of trapped charges leading to characteristic charging patterns around the injection point. Simulations also reproduce and clarify the origins of such phenomena as the drop/increase of the secondary electron yield to unity and the electrostatic mirroring effect. Analysis shows that the quality and proximity of the ground contact, the recombination velocity of the sample surface, and the transient nature of the yield may help to explain the apparent differences in the shapes of yield curves observed in various experiments.