Formation mechanisms of radial electron fluxes in a positive column

The main physical formation mechanisms of differential radial electron fluxes (i.e., of the fluxes which correspond to different parts of the distribution function) in a dc positive column are discussed. It is shown that the magnitude and even sign of these fluxes depend crucially on whether the electron distribution is local or nonlocal and on electron energy. In the case of a nonlocal electron distribution the flux of slow electrons in the body of the distribution function is directed outward (to the wall), and for the fast electrons both directions are possible. The flux directed outward results from escape of the electrons to the tube wall, and the flux directed inward is caused by inelastic collision with large energy losses. In the local case the flux of the fast electrons, with the exception of a small wall vicinity, is directed inward, and the fluxes of the electrons in the distribution body are directed both inward and outward depending on the energy relaxation law.