Excitation of the Azimuthal Surface Waves in Electron Cyclotron Frequency Range by Rotating Electron Beam in a Coaxial Waveguide

The initial stage of interaction between gyrating beam of electrons, which move along Larmor orbits in a narrow gap between a cylindrical plasma layer and an external screen of a metal coaxial waveguide, and electromagnetic eigenwaves is studied theoretically. These waves are extraordinary polarized; they propagate along the azimuthal angle across an axial external steady magnetic field in the electron cyclotron frequency range. The numerical analysis shows that existence of internal metal conductor affects the magnitude of the growth rate weakly. It narrows the range of effective wavenumbers within which effective wave excitation takes place when compared with the case of absence of this conductor. Excitation of these modes is found to be impossible for resonators with relatively small external radii and low plasma densities when compared with a similar structure completely filled with plasma.