Excitation of Azimuthal Surface Waves Above the Upper-Hybrid Frequency by External Relativistic Flows of Electrons in Coaxial Plasma-Vacuum Waveguide

Excitation of extraordinarily polarized azimuthal surface eigenwaves is shown to be possible in the frequency range above the upper-hybrid resonance in coaxial waveguides with metal walls, which are partially filled by cold magnetoactive plasmas. Interaction of these waves with the flow of electrons, which rotate around the plasma column in the gap separating the plasma from the waveguide wall, is studied. By employing the numerical methods, it is shown that the conditions of resonant interaction of the electron beam with these high-frequency azimuthal surface waves can be achieved in the case of sufficiently strong external magnetic fields without passing into the regime of the ultrarelativistic velocities of the beam electrons.