Non-axisymmetric slowed structure and plasma modes in a waveguide with a dielectric rod and magnetized plasma

Electrodynamics of a circular waveguide with a dielectric rod and plasma layer adjoining the rod surface is considered. The dispersion relation has been derived in the general case of non-axisymmetric perturbations, and its numerical solutions corresponding to slowed structure and plasma modes have been studied, mostly for hybrid waves combining properties of structure and plasma modes. For the structure fundamental HE11 mode, plasma parameters have been identified that prevent a Cherenkov interaction of this mode with a relativistic electron beam at a given frequency. For both structure and plasma modes, coupling impedances and percentages of RF power transmitted through the dielectric, plasma, and vacuum regions were calculated depending on plasma density. Mutual transformation of the field structure in hybrid waves has been shown. Results of the phase velocity and coupling impedance calculations are analyzed from the standpoint of operation of an antenna-amplifier device, a relativistic traveling wave tube in the HE11 mode of a dielectric rod: the concept realizability with plasma presence is proved and the role of non-axisymmetric and symmetric plasma modes is discussed.