Measurement of electron drift, diffusion, and effective ionization coefficients in the SF6–CHF3 and SF6–CF4 gas mixtures

Abstract

The electron drift velocity, the longitudinal diffusion coefficient, the effective ionization coefficient and the limiting field strength for mixtures of SF6 with CHF3 and CF4 have been measured with a pulsed Townsend technique. The overall density-reduced electric field strength, E/N, could be varied between 60 and 520 Td (1 Td = 10−17 V cm2), while the SF6 content in the gas mixtures was varied over the range 1–50%. We have found that the electron drift velocity and the density-normalized longitudinal diffusion coefficient vary weakly with the amount of SF6 in the mixture. In contrast, the effective ionization coefficient shows a strong dependence with the SF6 content, becoming more electronegative as the amount of SF6 is increased. The measured limiting field strength for these two mixtures is lower than those for SF6–N2. To our knowledge, no previous ionization or electron transport data for these mixtures have been published.