Effect of air admixture in helium on the rate of the breakdown current rise

The influence of dry air admixtures on the breakdown mechanism of helium in small gap separations was investigated using plane parallel stainless-steel electrodes enclosed within a Pyrex chamber. The experiments, carried out using different admixtures of air, shown that the time constant of the rate of breakdown current rise is a linear function of the product of the overvoltage across the gap and the partial pressure of the admixture. An empirical formula is derived to express this linear relationship. The rate of the breakdown current rise is calculated, using a quantitative model of the breakdown process; although these values somewhat exceed the experimental ones, the theoretical and experimental values are found to converge when measurements are performed at a slightly elevated relative partial air pressure of 3×10^-4