Electron impact ionization and attachment, drift velocities and longitudinal diffusion in CF3I and CF3I–N2 mixtures

Abstract

This paper reports the measurement of the electron drift velocity ve, the longitudinal diffusion coefficient NDL and the density-normalized effective ionization coefficient (α − η)/N in pure CF3I and in the CF3I–N2 mixtures, where α and η are the electron impact ionization and attachment coefficients, respectively, and N is the gas density. The E/N range covered was 100–850 Td (1 Td = 10−17 V cm2). The present results were derived from a pulsed Townsend experiment. For pure CF3I, the values of ve and (α − η)/N were found to increase linearly with E/N. Moreover, the E/N value at which ionization equals attachment, commonly referred to as the limiting field strength, was found to be E/Nlim = 437 Td, which is greater than that of SF6 (360 Td), a widely used insulating gas. For the CF3I–N2 mixture with 70% CF3I, this E/Nlim value was found to be essentially the same as that for pure SF6.