High voltage research (breakdown strengths of gaseous and liquid insulators). Semiannual report, April 1--September 30, 1978

The work on gas dielectric mixtures continued to focus on carefully chosen combinations of electron attaching and electron slowing-down gases. Experimental evidence relating the electron attachment cross section to the dielectric strength is discussed. Conclusions are reached as to the relation of molecular structure to the electron attaching properties of dielectric gases. A variety of mixtures of SF/sub 6/, Ar, Ne, and N/sub 2/ have been studied to determine the relative importance of electron impact ionization and electron scattering on the breakdown voltage, V/sub s/. Electron scattering (especially in the subexcitation energy range) was found to influence V/sub s/ much more critically than electron impact ionization. Preliminary studies involving mixtures of the polar molecules (1,1,1-CH/sub 3/CF/sub 3/, CHF/sub 3/, and CH/sub 2/F/sub 2/ with SF/sub 6/ and N/sub 2/ showed that electron-dipole scattering does not significantly affect V/sub s/. Field-induced electron detachment from negative ions--which has often been cited as a possible cause of a host of phenomena in gas breakdown studies--has been investigated, and the results of this investigation are reported.