Electron impact ionization and attachment, drift velocities and longitudinal diffusion in CF₃I and CF₃I–N₂mixtures

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.