High-Brightness Gaseous Field ION Source for Light ION Species

Abstract

We have reported on the very high brightness gaseous field ion source that has been developed at Cornell to produce high angular current density H2+ ion beams with low energy widths. Axially oriented H2+ ion beams from single emission sites with angular currents dl/dΩ= 10-20 μa/sr are obtained routinely. The energy width (FWHM) has been measured to be Δe=1.0 ev. H2+ beams with angular currents as high as 70 μa/sr. have been observed, but these higher current beams have a tail spread on their energy distribution curve.We have now extented this source to produce ion species of He+ with angular current densities, dl/dΩ, in the 10-15 μa/sr range and ions beams of Ne+, A+, N2+ and O+ ions with angular currents dl/dΩ of 3-7 μa/sr.Ion beams with these characteristics have have been achieved by operating the gaseous field ion source under the following conditions:1. In an ultrahigh vacuum system at cryogenic temperatures cooled with LHe and heated to obtain an optimum balance of gas concentration at the emitter tip with physisorption on the tip at temperatures that allow good surface transport from a large area near the apex of the tip to the emission site.