Electron energy distribution and transport coefficients of electron swarms in SF6 and nitrogen mixtures

Electron swarm behaviour in SF6 and nitrogen mixtures is analysed over the E/N range from 141 to 707 Td by a three-term Boltzmann equation method. A set of electron collision cross sections, which was determined consistently with measurements for the respective pure gases by the authors ((SF6, Itoh et al., 1988); N2(Ohmori et al., 1988)), is used. The calculation is carried out for the steady-state Townsend (SST), pulsed Townsend (PT) and time-of-flight (TOF) experiments. In particular the TOF parameters of these mixtures are deduced for the first time as far as the authors are aware. It is found that the calculated values of the effective ionisation coefficient alpha shows a monotonic variation with percentage of SF6 at a fixed E/N, the same as previous measurements. The E/N value at which alpha =0, i.e. the limiting E/N, is also deduced and in close agreement with measurements. The variations of the electron energy distribution and other transport coefficients with the partial SF6 pressure are calculated and discussed in detail.