Excitation of microwave by a thin annular relativistic electron beam in a plasma-filled dielectric-loaded coaxial cylindrical waveguide

A new type of slow-wave structure, i.e., plasma-filled dielectric-loaded coaxial cylindrical waveguide with a dielectric ring tightly enclosing the inner conductor, is developed. The collision between electrons and ions in the background plasma is taken into account. The microwave generation based on the Cherenkov effect excited by a thin annular relativistic electron beam in the new slow-wave structure is examined by use of the self-consistent linear field theory, considering the effect from this kind of collision via the collision frequency n_e,i term. The dispersion equation of the beam-wave interaction with a complex value of angular frequency is derived. The effects of the plasma angular frequency and collision frequency on the dispersion characteristics, i.e., the output frequency and the wave growth rate of the microwave radiation, are calculated and discussed. It is clearly shown that the microwave radiation excited by the beam-wave interaction results from the coupling between the slow TM modes propagated along the slow-wave structure and the negative-energy space-charge wave propagated along the relativistic electron beam.