The role of initiatory electrons in highly nonuniform field breakdown

The effect of initiatory electrons in SF/sub 6/ and mixtures of SF/sub 6/ with N/sub 2/ and SF/sub 6/ with air has been studied by varying the population of free negative ions. It has been found for all gases studied that the dielectric strength of the gas is a decreasing function of the ion population although it appears that there is something of a saturation effect in that as the ion population is increased, the breakdown strength becomes progressively less sensitive to further increase in the ion density.