The Cherenkov instability used in slow-wave devices has been well studied in the literature. However, in previous analyses, the beam motion is restricted to the longitudinal direction assuming an infinitely strong magnetic field. For the finite strength magnetic field, the transverse beam perturbation cannot be ignored and leads to the slow cyclotron instability. Recently, a new version of self-consistent field theory considering three-dimensional perturbation has been developed based on a solid beam, in which the effect of the transverse perturbation appears as a surface charge at a fixed boundary. In the case of a thin annular beam, the boundary is modulated and is essentially different from the solid beam case. We propose a self-consistent field theory considering the moving modified boundary surface. The slow cyclotron instability due to the modulation of an infinitesimally thin annular electron beam is presented.
We report an oversized K-band backward wave oscillator (BWO) operating above 20 GHz in the weakly relativistic region less than 100 kV. It is very important to prevent microwave from going into the beam diode, since intense microwaves will harmfully affect beam generation. A weakly relativistic oversized BWO is demonstrated using a Bragg reflector at the beam entrance of slow wave structure (SWS). The effect of the Bragg reflector on the BWO operation is examined, by changing the boundary condition at the beam entrance. The Bragg reflector improves the performance of the oversized BWO.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.