Hydrodynamic description of electron flow to an absorbing anode

A theory is presented of the nonequilibrium space-time development of a stream of electrons moving through a background medium under the influence of a strong electric field. Nonequilibrium processes are treated by supplementing the usual continuity moment equation with equations describing the velocity and energy moments of the electron distribution. It is shown that the theory is able to reproduce many of the important nonequilibrium effects occurring as an electron stream approaches an absorbing anode, although comparison with detailed solutions of the Boltzmann equation does reveal certain limitations apparently inherent in theories based on moment equations.