Eur. Phys. J. D 65, 489-498 (2011)
https://doi.org/10.1140/epjd/e2011-20296-7

Regular Article

Effect of small admixtures of N₂, H₂ or O₂ on the electron drift velocity in argon: experimental measurements and calculations

¹ Comenius University, Mlynska Dolina F2, 84248 Bratislava, Slovakia
² Nuclear and Technological Institute, Estrada Nacional 10, 2686-953 Sacavém, Portugal
³ Leibniz Institute for Plasma Science and Technology, Felix-Hausdorff-Str. 2, 17489 Greifswald, Germany
⁴ Research Institute for Solid State Physics and Optics, 1525 Budapest, P.O. Box 49, Hungary

^a e-mail: stano@fmph.uniba.sk

Received: 19 May 2011
Received in final form: 26 October 2011
Published online: 1 December 2011

Abstract

The electron drift velocity in argon with admixtures of up to 2% of nitrogen, hydrogen or oxygen is measured in a pulsed Townsend system for reduced electric fields ranging from 0.1 Td to 2.5 Td. The results are compared with those obtained by Monte Carlo simulations and from the solution of the electron Boltzmann equation using two different solution techniques: a multiterm method based on Legendre polynomial expansion of the angular dependence of the velocity distribution function and the S_n method applied to a density gradient expansion representation of the distribution function. An almost perfect agreement between the results of the three numerical methods and, in general, very good agreement between the experimental and the calculated results is obtained. Measurements in Ar-O₂ mixtures were limited by electron attachment to oxygen molecules, which contributes to the measured drift velocity. As a result of this attachment contribution, the bulk drift velocity becomes larger than the flux drift velocity if attachment is more probable for electrons with energy below the mean value and smaller in the opposite case. Attachment also contributes to the negative differential conductivity observed in Ar-O₂ mixtures.