Eur. Phys. J. D (2012) 66: 77
https://doi.org/10.1140/epjd/e2012-20676-5

Regular Article

Measurement of electron swarm coefficients in C₂F₄-Xe and evidence of Penning ionization in C₂F₄-Ar

¹ Instituto de Ciencias Físicas, Universidad Nacional Autónoma de México, P.O. Box 48-3, 62251 Cuernavaca, Mor., México
² Departamentos de Energía y de Ciencias Básicas, Universidad Autónoma Metropolitana-Azcapotzalco, Av. San Pablo 210, 02200 México, D.F.

^a e-mail: jdu@fis.unam.mx

Received: 24 November 2011
Received in final form: 25 January 2012
Published online: 27 March 2012

Abstract

We have measured the electron drift velocity, the effective ionization coefficient, and the longitudinal diffusion coefficient of electrons in the C₂F₄-Xe mixtures with 1% and 5% amount of C₂F₄. The electron drift velocity curves show a well defined region of negative differential drift velocity, and a similar effect is found for the density-normalized longitudinal diffusion coefficients at low E/N values. Previous findings of possible Penning ionization effects on the pulse shapes in the C₂F₄-Ar mixtures were not found in C₂F₄-Xe. This effect is further explored in this paper and fully supported by the simulation of avalanche development in the C₂F₄-Ar mixtures in which, apart from electron transport and effective ionization, the formation of metastable Ar^∗ followed by ionization of C₂F₄ has been included. In most cases the comparison between simulations and measurements is very good, thereby giving further support to the original hypothesis.