On the role of the electron impact ionisation and electron scattering cross-section in the breakdown strength of dielectric gases

Abstract

Discusses the role of the electron impact ionisation cross-section sigma _i( epsilon ) and the electron scattering cross-section sigma _sc( epsilon ) as a function of electron energy epsilon in the breakdown strength of gases/mixtures. Four gases (Ne, Ar, N₂ and SF₆) were chosen for which sigma _i( epsilon ) and sigma _sc( epsilon ) at low energies are known. Direct-current breakdown strength measurements on Ne, Ar, (Ne+SF₆), (Ar+SF₆), (N₂+Ne+SF₆) and (N₂+Ar+SF₆) were made and are reported, using sphere-on-sphere to sphere and square-rod to plane electrode geometries. On the basis of these measurements and the data on sigma _sc( epsilon ) and sigma _i( epsilon ) it was concluded that the magnitude of sigma _sc( epsilon ) at subionisation ( epsilon i( epsilon ). The effect of perfluorination and static polarisability on sigma _i( epsilon ) is also discussed.