LINEAR-ANALYSIS OF CYCLOTRON-CHERENKOV AND CHERENKOV INSTABILITIES INDIELECTRIC-LOADED COAXIAL WAVE-GUIDES

We present, based on the cold fluid theory, linear analysis of the Che renkov and cyclotron-Cherenkov instabilities which are driven when a l inear electron beam is injected into a dielectric-loaded waveguide imm ersed in an axial magnetic field. In the analysis we consider azimutha lly symmetric TM(On) modes. We derive dispersion relations for three t ypes of waveguide, and compare computationally obtained linear growth rates of both instabilities. For the type A, which consists of a metal lic cylinder with dielectric liner on its inner surface, the growth ra te of the Cherenkov instability is larger than that of the cyclotron-C herenkov instability. For the type B, which consists of a dielectric c ore and an outer metallic cylinder, both growth rates are comparable. And for the type C, which consists of a metallic core with dielectric liner on its surface and an outer metallic cylinder, the growth rate o f the latter instability is higher than that of the former instability . Finally, for the type C, obtained are dependences of the oscillation frequency and the growth rates of both instabilities on the following parameters: the beam energy, the beam current, the axial magnetic fie ld, the dielectric constant, and the thickness of the dielectric.