ABSTRACT
Electron bombardment ion sources are mainly used in areas where a well-defined electron energy is requested and a moderate ion current is sufficient. The design of an electron bombardment ion source can be simple and cheap. Energy of the ionizing electrons is uniform and the energy spread of the ions small. This is called the forced electron beam-induced arc discharge mode. With increasing electron energy, higher charge states may also be created by single or multiple impacts. The latter is more likely at higher ion densities in the discharge mode. Electron bombardment ion sources have been investigated by many people starting with Dempster in 1916. Various designs have been published; the most important for application are the Nier, Bernas, and Nielsen types. The Bernas source contains a single-turn helical filament at one side of the arc chamber and a reflector at the other side.
