Cyclotron-Cherenkov instability in dielectric-loaded circular waveguides

When a linear electron beam is injected into a dielectric-loaded waveguide immersed in an axial magnetic field, Cherenkov and cyclotron-Cherenkov instabilities appear. We report computational results on linear growth rates of both instabilities for three types of waveguides. For the first type which consists of a metallic cylinder with dielectric liner on the inner surface, the growth rate of Cherenkov instability is larger than that of cyclotron-Cherenkov instability. For the second type which consists of a dielectric core and an outer metallic cylinder, both growth rates are comparable. For the third type which consists of a metallic core with dielectric liner on the surface and an outer metallic cylinder, the growth rates of the latter instability is higher than that of the former. The case of the third type is investigated at some length. Effects of thermal spread of the beam are included.