To generate a plasma for processing a workpiece, an electron beam is introduced into a plasma reactor chamber by radial injection using an annular electron beam source distributed around the circular periphery of the chamber to provide azimuthal uniformity. The electron beam propagation path is tilted upwardly away from the workpiece, either by tilting the electron beam source or by a magnetic field. In other embodiments, there are plural opposing electron beams from linear electron beam sources directed toward the center of the plasma reactor chamber.