NONLINEAR COUPLING OF A SUPERLUMINAL ELECTROMAGNETIC-WAVE TO A RELATIVISTIC ELECTRON-BEAM

The nonlinear propagation of a superluminal, linearly polarized electr omagnetic wave in the presence of a relativistic cold electron beam is investigated. At large amplitudes the wave couples to the electron-be am plasma mode owing to two important nonlinear effects, namely the re lativistic variation of the electron mass and the excitation of longit udinal space charge fields by strong vxB forces. The nonlinear propaga tion equations for the coupled electromagnetic and longitudinal waves are derived within the context of a relativistic cold-fluid model. Non linear travelling-wave solutions are sought to describe the saturated state of the coupled system. Using Hamiltonian techniques, a wide vari ety of solutions are obtained and their characteristics discussed.