Electron transport and effective ionization coefficients in C2F6, C2F6–Ar and C2F6–N2 mixtures

Abstract

The electron drift velocity, the longitudinal diffusion coefficient and the effective ionization coefficients in C2F6 and its mixtures with Ar and N2 have been studied in a pulsed Townsend experiment. The density-reduced electric field strength E/N, was varied widely in the range 0.1–500 Td (1 Td = 10−17 V cm2). In all cases, negative differential conductivity (NDC) regions were found in the plots of the electron drift velocity as a function of E/N. Our drift velocity values were found to be in good agreement with previous work on C2F6 and its mixtures. In some cases, the E/N range was increased. The longitudinal diffusion coefficient also displays the NDC effects; these are more pronounced as the C2F6 content in the mixture decreases. The effective ionization coefficient for C2F6 was measured over a wider range of E/N than that covered by previous studies. Our effective ionization coefficients for C2F6 and those derived previously disagree strongly. We are not aware of any previously published data on effective ionization coefficients for the mixtures herein studied. The limiting field strength for C2F6–N2 turned out to be nearly a factor of two higher than that for C2F6–Ar, for C2F6 concentrations being less than 10% in both mixtures.