The negative glow(NG) in a low pressure He and a He–Cd glow discharge was investigated by a spectroscopic method. Atomic line intensities and their excitation cross-sections were utilized to estimate the electron energy and density in the NG. In the NG, some electrons have the energies more than 100 eV and the density of low energy (30–34 eV) electrons is larger than in the positive column (PC) by two orders of magnitude. Using a plane parallel type hollow-cathode, the line distribution and intensities can be controlled by changing the inter-cathode distance. In the case of He–Cd discharge, the main component of emission spectra can be controlled between the ionic lines of Cd and the atomic lines of He by changing only the intercathode distance. The most significant property of the NG for applications regardless of the gas composition is the presence of high energy electrons.
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Kan-ichi Fujii (1977) studied this question.