Single hot spot discharge in SF 6 gas and in the mixture SF 6 /C 2 H 6

Abstract

Dynamics of development of single hot spot discharge in SF<SUB>6</SUB> gas and in the mixture SF<SUB>6</SUB>/C<SUB>2</SUB>H<SUB>6</SUB> and of its contraction has been studied experimentally. Visualization of discharge development has been performed by a fast shutter CCD camera. Discharge properties have been studied in a wide range of current densities and input energies. It has been found that a single hot spot discharge has a cup- like structure. The diameter of the cathode hot spot is 0.04 cm, while the diameter of the plasma near the anode reach a value of about 3 cm. An increase of the discharge current causes an enlargement of the discharge cross section. The hypothesis of discharge widening is presented and discussed. It has been shown that discharges in the mixture are more homogeneous and stable. Single hot spot allows to realize a discharge current of 2 - 3 kA at input energies of about 1 - 3 J without distortion of discharge homogeneity. When the discharge with three hot spots separated by 5 mm has been investigated, the formation of inhomogeneity from one hot spot occurs at 700 A. Development of a channel with enhanced conductivity from single hot spot in SF<SUB>6</SUB> gas has been also obtained experimentally in case with advanced preionization.