Efficient microwave generation in a beam-waveguide system with an annular plasma sheet

A linear theory is presented to describe microwave generation in a system, composed of a smooth, cylindrical waveguide with an annular plasma sheet and a pencil beam, in the presence of a strong, axial magnetic field. The plasma sheet is assumed to be a very thin shell, with a radius larger thin the radius of the beam to avoid mode competition. The exact dispersion relation for the fundamental mode is derived, and analytic expressions for the frequency, wavenumber and the growth rate are obtained in terms of the system parameters, for the short wavelength limit. Good agreement with the recent Soviet experiments is found. >