Cherenkov interaction of a hollow relativistic electron beam with RF fields of a disc-loaded rod antenna in a circular waveguide

The instability of an electron beam propagating within the slow-wave supporting structure comprising an inner disc-loaded conducting rod and an outer circular waveguide is considered. The linear theory is developed in the one-wave approximation, i.e., not taking the space harmonics into account. The complex solutions of the derived dispersion relation are investigated numerically for the fundamental mode of the system, the quasi-TEM mode. The results are compared with the case of an inner dielectric rod, for which the fundamental mode is the non-axisymmetric HE₁₁ mode. The possibility of using the disc-loaded rod antenna in a hybrid antenna-amplifier device is discussed. For the disc-loaded conducting rod, spatial growth rates are higher due to stronger beam-wave coupling at given beam-rod distances, and amplification bands are wider due to weaker dispersion of the quasi-TEM mode; however, for the dielectric rod, the issues of the microwave drive signal input are significantly easier.