Stability of a transverse electromagnetic wave in electrons streaming parallel to an external electric field

The stability of a circularly polarized electromagnetic wave convected by a dense electron beam in an external longitudinal electrostatic field is studied. It is shown that when the electron density in the stream is high enough the amplitude a of the wave is an S-shaped function of the potential U of the longitudinal field (in the quasistatic approximation). An approximate solution is found for the self-consistent problem. This is compared with the results of numerical simulation and the linear perturbation theory, which makes it possible to demonstrate and describe the instability of the quasistatic stream-wave system when the function a(U) is decreasing. The instability occurs regardless of the direction of the longitudinal field, associated with the negative sign of the wave energy, and can be interpreted as open-quotes slippingclose quotes of the fields inside the beam relative to the electron flow. The nature of the quasiequilibrium electron states when the function a(U) is decreasing is also discussed. 5 refs., 2 figs