Analysis of a rectangular grating Cerenkov maser

Summary form only given. Electron sheet beam propagation over a rectangular deep groove grating in a rectangular waveguide is considered. The lowest-order mode in the grating rectangular waveguide is the hybrid TE/sub x10/ mode. A complex dispersion relation for the hybrid modes an electron sheet beam interaction has been derived and analyzed. A finite axial energy spread in the beam is included in the dispersion relation. The growth rates for TE/sub x10/ and TE/sub x11/ hybrid modes are obtained. It is found that the growth rate of the TE/sub x11/ mode can be suppressed by allowing a small axial energy spread to the beam and a small increase in the beam-grading separation distance. With a 20 kV, 0.25 A, 3% axial spread electron beam and a 1 mm beam to grating separation distance, the growth rate of the TE/sub x10/ mode is 1 dB/cm. The absolute and convective nature of the interaction has been analyzed utilizing Briggs' criteria. It is found that the instability is always convective in the forward mode regime.