Mapping changes in helium sensitivity and peak shape for varying parameters of a Nier-type noble gas ion source

Abstract

Tuning a Nier-type ion source involves adjusting many different parameters which affect the resulting signal in complicated ways. We have mapped the sensitivity of 4He and the peak shape while varying the total extraction voltage, the half-plate bias, the repeller voltage, and the electron energy. With the particular source settings that we used, we see an asymmetric rise and fall in the sensitivity as the extraction is raised, but a symmetric rise and fall as the half-plate bias voltage is varied. The best peak shape is found generally at the same extraction value of the maximum sensitivity, but at a distinctly different half-plate bias than the maximum sensitivity; thus it is necessary to monitor the peak shape while tuning the half-plate bias. The extraction and the repeller values of the maximum sensitivity and the best peak shape are strongly correlated, and therefore these two parameters must be tuned together. And finally, we see a double-peak in the sensitivity as the electron voltage is increased, so it may be worthwhile to check a wide range of electron voltages when tuning.