Negative ion motion in the mixtures of SF6 with CF4 and CH4-Ar.

This paper deals with the measurement of the mobility of negative ions in the mixtures of SF 6 with CF 4 and the CH 4 -Ar (50:50) binary mixture with SF 6 contents up to 50%. The pulsed Townsend technique was used to observe the integrated ionic avalanches over a range of the density-reduced electric field E/N for which ionization is either negligible or absent, and attachment processes are significant, leading to the formation of mostly SF 6 -. The E/N range of measurement was from I to 70 Td ( 1 Td=10 - 1 7 V cm 2 ), over which the measured mobilities were found to be almost constant. The mobility of the negative ions was also measured for trace amounts of SF 6 in CH 4 and Ar and 1% CF 4 , thereby providing a good value of the mobility of SF 6 - in these pure gases, in order to test the measured mobilities with Blanc's law. We have found good agreement, within quoted experimental uncertainties. between calculated and measured values.