Time-resolved study on negative ion motion in SF₆ at high pressures

摘要

We have used a pulsed Townsend technique to measure the drift velocity of two negative ion species in SF₆ at low values of the density-normalized electric field intensity E/N, from 2.3 to 100 Td (1 Townsend = 10-17 V cm2), and very high pressures in the range 50-720 torr. Within experimental uncertainties of between 2-3%, we could group the observed mass-unidentified ionic reduced mobilities near the value of 0.48 cm2 V-1 s-1 and 0.42 cm2 V-1 s-1. This finding is consistent with the mobility ascribed to the clusters SF₆-SF₆ and SF₆-(SF₆)₂, respectively. These ions are assumed to be formed by ion-molecule reactions between SF₆- and the gas neutrals. Our findings may be of relevance for the modelling of high pressure SF₆ discharges, like those taking place in circuit breakers.