Ion extraction from the cathode-fall region of Ar, N2 and O2 discharges

Abstract A relatively simple experimental apparatus has been developed to extract ions from several d.c. plasmas, involving a symmetrical three-element einzel lens and mass spectrometric detection. The measured ion energy distributions obtained for Ar d.c. plasmas are in good agreement with the classical results of Davis and Vanderslice and conform to their model except that there must be at least one other type of ion which contributes to the observed energy distributions in addition to those which experienced charge exchange during their last collision in the cathode-fall region. This additional group of ions has been tentatively identified. The distributions from N 2 d.c. plasmas show larger deviations from the Davis and Vanderslice model; two consecutive processes may be at work which also have been specified. The O 2 + and O + results obtained were non-reproducible, presumably because of changes of the internal surfaces which affected the electrical fields in the ion optics.