The influence of the photosheath on the very low energy electrons during active potential control

Abstract

A low and actively controlled electrostatic potential on the outer surface of a scientific spacecraft is very important for the accurate measurement of the cold plasma electrons and ions. A small potential barrier <2 eV may emerge in the photoelectron sheath during the active potential control operation using energetic (some keV) ion beams. Although the measurement conditions are improved considerably, some very low energy electrons of the ambient plasma cannot overcome the potential barrier and return to the plasma. It is designated as the screen effect of the photosheath. In this paper, the relationship between the “hidden” low energy electron population and the parameters of the photosheath potential barrier, such as the height (<2 eV) and position of the potential barrier, is analysed. The domains of the “hidden” and “detectable” ambient plasma electrons in the velocity space are presented.