Excitation of Electromagnetic Waves Above the Upper-Hybrid Frequency by Internal Gyrating Electron Beam in a Coaxial Waveguide

The possibility to generate electromagnetic waves in the frequency range above the upper-hybrid frequency is demonstrated. In this frequency range, a plasma is a nontransparent medium for bulk electromagnetic waves. Effective interaction of an electron beam and extraordinarily polarized electromagnetic waves of surface type is provided by application of a gyrating beam of electrons, which move along large Larmor orbits in the gap between a cylindrical plasma layer and the inner conductor of a coaxial waveguide. These waves are composed of azimuthal and radial components of the electric field and an axial component of the magnetic field. The presence of the azimuthal electric field that is parallel to the electron velocity encourages their effective interaction. The beam excitation is most efficient in the case when the waves propagate in a coaxial waveguide whose parameters correspond to the right limit of the effective wavenumber range. Introduction of the inner metal conductor instead of the internal part of the beam-plasma system does not prevent wave excitation and allows installing there a source for the electron beam production.