The electron swarm behaviour in SF6 gas is studied for E/N values from 141 to 707 Td by a three-term Boltzmann equation method, in which the effect of generation and loss of electrons due to ionisation and attachment is considered properly. A consistent set of electron collision cross sections, which gives the swarm parameter values in agreement with previous measurements, is determined considering the latest cross section data. The calculation is performed mainly for the steady-state Townsend condition. The validity of the results obtained has been confirmed by a Monte Carlo simulation carried out parallel to the analysis. The present results are also compared with those of the usual two-term Boltzmann analysis. It is found that the two-term approximation is fully valid for deduction of the swarm parameters for E/N values as considered despite the fact that SF6 is a strongly electronegative gas.
Generally, in Townsend discharges, the behaviours of metastable molecules are treated by solving the diffusion equation. The boundary condition for the diffusion equation has previously been assumed to be that the density at the boundary is zero. Such an assumption is found to be unsatisfactory in determining effective lifetimes from the experimental data. The authors solve the diffusion equation using boundary conditions of the third kind. By adopting the two-stream approximation, the reflection coefficient of the metastables is introduced naturally into the theory. An expression which depends implicitly on the reflection coefficient is derived for the effective lifetime of the metastables as a function of pressure. By fitting the calculated curves to the experimental data, the authors succeed in determining the various physical parameters, including the newly introduced reflection coefficient.
The emission of repetitive streamer corona was observed by a photon counting method with a high time resolution. The half-width of the main pulse of the primary wave corresponding to the emission from the 0.014 mm length part in the direction of the electrode axis is found to be only 0.8 ns. This primary wave emission has the nature of transient developing glow discharge which has the cathode glow, cathode dark space and negative glow. The faint but steady build-up of emission which continues from the cathode toward the cathode glow, suggests a considerable secondary electron emission from the cathode during the period of the primary wave propagation.
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