Diffusion and drift of electrons in SF6

Measurements have been made of the drift velocities and the ratios of the diffusion coefficient to mobility ( D /μ) of electrons in SF 6 over the range 115< E/p <210 V cm −1 Torr −1 normalized to 20°C with gas pressures in the range 0·6 to 2 Torr and for diffusion gap distances of 3, 5 and 7 cm. In the derivation of the D /μ values, Townsend's primary ionization and electron attachment coefficients reported by Bhalla and Craggs (for the range 110 < E/p <160) and Moruzzi (for the range 160 < E/p <210) were used. The close agreement obtained between the D /μ values at various pressures and gap lengths supports the data of these workers. Anomalous diffusion of electrons was observed particularly at high pressures for E/p <130.