A coaxial waveguide partially filled with a dielectric as the slow-wav
e structure of a dielectric Cherenkov maser is investigated. The dispe
rsion of the fundamental made of this waveguide is very weak at phase
velocities close to the velocity of light, and for this reason a very
wide gain bandwidth is possible under conditions of an interaction wit
h a relativistic electron beam. The dispersion equation for an infinit
ely thin tubular beam in a coaxial waveguide with a dielectric liner a
djoining either the outer or inner conducting surface is derived. The
gain bandwidth as a function of the parameters of the electron beam an
d the slow-wave system are investigated on the basis of numerical solu
tion of the dispersion equation, and a comparison with similar depende
nces for the conventional configuration of a dielectric Cherenkov mase
r is made. The structural features of the coaxial configuration which
enable novel approaches to the problems of matching the microwave sign
al at the entrance and exit of the system are discussed. (C) 1997 Amer
ican Institute of Physics. [S1063-7842(97)01504-3].