On the Theory of the Diffusing Electron Stream in a Gas

A theoretical discussion is presented of the structure of a stream of electrons moving through a gas under the action of a uniform electric field. The treatment incorporates the phenomenon of longitudinal diffusion in which the coefficient DL can be different from the isotropic coefficient of diffusion D. The treatment also is not restricted to the case in which the aperture through which the stream enters the diffusion chamber is small. The solution satisfies the boundary condition n = 0 at the surface of the anode and everywhere on the cathode except over the plane of the source aperture. The theory therefore provides criteria for the validity of simplified solutions employed hitherto.