Experimental and theoretical investigations of an electrical discharge in SF6 gas

Results of experimental and theoretical investigations of a homogeneous discharge in SF6 gas have been presented. Experiments with use of electrodes made of Al have clarified that even by small current densities (below 20 A/cm(2)) and pulse durations (50 ns) the cathode surface is covered by a number of hot spots, which influence discharge homogeneity and stability. The hot spot density of about 10 cm(-2) is found to be necessary for ignition of a homogeneous discharge. In order to achieve desirable hot spot density special kinds of cathodes with predefined hot spot number have been designed. These cathodes have provided high discharge homogeneity and stability. Self-consistent numerical model of a homogeneous discharge in SF6 gas has been developed. The model includes the system of equations for electrical circuit, time-dependent Boltzmann equation for determination of electron kinetics, the system of rate equations for different heavy particles, and, the equation for determination of the gas temperature. Theoretical investigations have been shown that stepwise ionization processes and attachment to vibrationally excited SF6 molecules strongly influence characteristics of discharge plasma. The model has been tested by means of comparison of calculated and measured discharge currents and plasma voltages in a wide parameter range.