Theory of the Townsend Method of Measuring Electron Diffusion and Mobility

Abstract

The Lorentz method is applied to the combined drift and diffusion of the electron stream in the Townsend experiment. The zeroth-order approximation is found to lead to the equation found by Townsend. It is shown how the next approximation is obtained. The same method is then applied to the drift of electrons in crossed electric and magnetic fields. It is found that the magnetic field changes the energy distribution as well as the direction of drift. The latter is found in close agreement with Townsend, but not with Huxley.