Experimental determination of first Townsend ionization coefficient in mixtures of He and N2

Abstract

Abstract First Townsend ionization coefficient α in gas mixture of He with N2 is relevant for modeling of the development and chemical activity of atmospheric pressure plasma jets. This study determined α from measurements of current versus electrode separation in a steady-state non-self-sustaining Townsend discharge set-up. The measurements were carried out in absolute pressure range of 10–800 Torr and reduced electric field E/N range of 20–1000 Td. The effect of the N2 concentration in the gas mixture on the density normalized ionization coefficient α/N depended on the reduced electric field strength E/N. At E/N values below 200 Td, increased N2 content reduced the α/N while at E/N values above 200 Td, increased N2 content increased the plateau value of α/N. Reasonably good coincidence was observed between calculation performed with Bolsig+ and measured α/N. The discrepancy between experimental results and calculations at N2 percentage in the mixture below 5% and E/N values below 200 Td can be attributed to the Penning effect.