Anomalous secondary electron emission of metallic surfaces exposed to a Glow Discharge plasma

Abstract

Secondary electron emission (SEE) yields, γ, of Li, stainless steel (SS) and W surfaces immersed in a He Direct Current Glow Discharge (dc-GD) Plasma have been calculated from the experimental I–V curves as a function of electron mean energy. The data obtained showed that γLi > γSS > γW. Line emission ratios 728/706 of excited He and Langmuir probe measurements provide a clear evidence of the presence of a suprathermal electron tail responsible for the observed SEE. The results show that SEE is well correlated with the anomalous extra current component found in the I–V curves. The resulting value of γLi is significantly higher than its theoretical value suggesting a possible synergetic effect of the ion bombardment in the SEE of lithium. The effect of Li surface oxidation has also been addressed, leading to a substantial decrease of both, sputtering yield and SEE yield of Li with higher oxygen content.