Boltzmann-equation analysis of electron transport properties in CCl2F2/SF6/N2 gas mixtures

Abstract

A Boltzmann-equation analysis has been used to study electron swarm phenomena in ternary gas mixtures of N2, SF6 and CCl2F2. Electron energy distribution functions, collision frequencies and transport coefficients have been calculated for a number of cases with percentage mixture ratios ranging from 0 to 100%, for either of the electronegative components and, from 0 to 66.7%, for N2. The distribution function is presented for selected compositions with 0 or 50% N2 content and several percentage mixture ratios of SF6 and CCl2F2; its variation with partial contents of the gas components is discussed in terms of collisional cross sections. Ionisation ( alpha ) and attachment ( eta ) coefficients, drift velocity (V) and the diffusion coefficient to mobility ratio (D/ mu ) are shown as a function of the reduced electric field E/p20 for the particular percentage mixture ratios 40:10:50(%), 10:40:50(%) and 16.7:16.7:66.6(%) of CCl2F2, SF6 and N2, respectively. The theoretical limit-field values, defined by the condition alpha = eta , range from 75 to 122.5 V cm-1 Torr-1 and are found to agree well with breakdown-potential measurements reported in the literature.