Pulsed Townsend measurement of electron transport and ionization in SF6–N2 mixtures

Abstract

The pulsed Townsend (Td) technique was used to measure the electron drift velocity, the longitudinal diffusion coefficient and the effective ionization coefficient in the SF6–N2 mixture for SF6 concentrations of 0.02%, 1%, 10%, 20% and 30% SF6, over a wide range of the reduced electric field strength E/N, from 50 to 360 Td (1 Td = 10−17 V cm2). In the overlap ranges, these swarm parameters were found to be in good agreement with values previously measured by Aschwanden, who used the same technique. However, some of the present data do not match recent calculations. At the limiting value of E/N for these mixtures, the measurements of Aschwanden for the ratio of the longitudinal diffusion coefficient to the electron mobility agree very well with ours, which were measured over a wide E/N range. A well-defined trend of the longitudinal diffusion coefficients with the SF6 content in the mixture was found to be in excellent agreement with a previous three-term Boltzmann calculation. To our knowledge, no previous experimental values of these coefficients have been published in the literature.