Drift velocity of ions in lighter gases in electric and magnetic fields

Abstract

The general expression of the drift velocity (as well as the related conductivity tensor) of atomic ions in atomic gases in static electric and magnetic fields is obtained under the hypothesis that the ion mass is sufficiently greater than the neutral mass (quasi-Rayleigh gas). The starting point of the theory is an appropriate approximate (differential) form of the Boltzmann equation. The results and their limits of validity are discussed and extended to the more general case in which the ions move in gas mixtures. In the light of these results, the alternative non-rigorous “momentum-transfer theory” is analysed and its inaccuracies and drawbacks are pointed out.