Is CF3I a good gaseous dielectric? A comparative swarm study of CF3I and SF6

Abstract

This paper deals with the measurement of the electron drift velocity, the longitudinal diffusion coefficient and the effective ionisation coefficient in pure CF3I and CF3I mixtures. 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 the electron drift velocity and of the effective ionisation coefficient were found to increase steadily with E/N. The E/N value at which ionisation equals attachment, commonly referred to as the limiting field strength, was found to be E/Nlim=437 Td, which is higher than that of SF6 (360 Td), a widely used insulating gas. Moreover, the curve for the mixture of 70% CF3I with N2 is very similar to that of SF6 in the neighbourhood of E/Nlim. Thus, from the point of view of these coefficients, CF3I would seem to be superior in dielectric behaviour to SF6. Besides, CF3I is an environmentally friendly gas as opposed to SF6. Certainly, many more tests should be performed to regard CF3I as a good dielectric and possible substitute to SF 6. © 2007 IOP Publishing Ltd.