Forced scattering of electromagnetic waves on electron beam in periodically inhomogeneous plasma

Parametric processes of excitation of short-wave electromagnetic radiation in periodically inhomogeneous plasma waveguide were investigated. Parametric processes were considered both under conditions of the absence of plasma-beam instability and under the conditions of its development. It is shown that in the first case more complex two-cascade processes (when the beam excites LF+pumping wave on one hand, and scattering on the beam of this wave leads to excitation of HF-radiation - on the other hand) are possible along with parametric Cherenkov mechanism of HF-radiation excitation. Initial stage of these processes was investigated. Excitation of HF-radiation developes most rapidly under conditions of plasma-beam instability. In this case the unstable plasma wave is in parametric resonance with back plasma wave which represents a pumping wave. 17 refs