Measurement of ionization and attachment coefficients in SF6 and SF6+N2

Prebreakdown ionization currents have been measured in SF6, N2, and SF6+N2 mixtures by the Townsend method over the E/p range 100–450 V cm−1 Torr−1. A digital computer analysis is used for evaluation of the ionization and attachment coefficients. The variation of (α−η)/p in SF6 and N2 mixtures is found to be nonlinear with the percentage mixture ratio. Sparkover voltage measurements are carried out for SF6, N2, and SF6+N2 mixtures in the pd interval of 3.5≤pd≤25 Torr cm. Furthermore, the apparent secondary ionization coefficients have been deduced in SF6+N2 mixtures. They decrease significantly with increasing partial pressure of SF6. The reduction observed in this coefficient is attributed to the increased photon absorption coefficient.