The critical reduced electric fields in SF6 at high gas temperatures

Abstract

In this paper, the critical reduced electric fields (E/N)cr in SF6 are determined over a temperature range 298–2300 K. These fields are derived from the quasi-stationary burning voltages of a self-sustained volume discharge in SF6 irradiated by a CO2-laser through a slit diaphragm. Visualization of the shock-wave disturbances generated by the temperature jump at the boundary between the laser-heated and cold gas and measurements of the discontinuity surface propagation velocities are performed. A purpose-developed VSh method allowing determination of the gas temperature T by the shock wave propagation velocity has been proposed to evaluate the temperatures exceeding 1500 K. The (E/N)cr-values obtained at T > 2000 K are compared with those measured under the conditions of the complete thermodynamic equilibrium. The difference found is treated in terms of the authors' concept of the dielectric strength of strongly heated electronegative polyatomic gases. A number of fundamentally new physical effects are shown to arise at the discontinuity surfaces in a shock-wave-disturbed SF6 after voltage application. Some aspects of relevance to these effects are qualitatively discussed. Special attention is given to the dynamic barrier effect.