Space-Charge Lens for Focusing Negative Ion Beams by Means of an Additional Electron Ionizer

A space-charge lens created at the Institute of Physics, National Academy of Sciences of Ukraine, to focus negative ion beams using an additional electron ionizer is investigated. In the previous version of the lens, in which the gas was ionized by the ion beam itself, the focal power was quite high (the focal length was f ≤ 20 cm) but the gas pressure was too great (P ∼ 10-3 torr), which resulted in significant charge-exchange losses of the beam ions. The experimental and theoretical study reported here shows that the use of a 100-eV electron beam as an auxiliary ionizer allows the working pressure in the lens to be significantly reduced. As a result, a simple, inexpensive, and efficient lens has been developed that can be used in systems for transportation of negative ion beams