Test of Blanc's law for negative ion mobility in mixtures of SF6 with N2,O2 and air

We have measured the mobility of negative ion species drifting in mixtures of SF6 with N-2, O-2 and air. The pulsed Townsend experiment was used for this purpose. The conditions of the experiment, high pressures and low values of the reduced electric field, E/N, ensured that the majority species drifting in the gap was SF6-, to which the present mobilities are ascribed. The extrapolated, zero field mobilities for several mixture compositions were used to test them successfully with Blanc's law. Moreover, the measured zero field SF6- mobilities in air could also be explained in terms of the measured mobilities for this ionic species in N-2 and O-2.