WAVE-DISPERSION AND GROWTH ANALYSIS OF LOW-VOLTAGE GRATING CERENKOV AMPLIFIERS

A theoretical and computational investigation of an electron sheet bea m propagating over a grating structure in a rectangular waveguide is c arried out. Regimes for low voltage Cerenkov amplifier operation are s ought by examining the complex dispersion relation for hybrid waveguid e modes in the slow wave structure, which includes sheet beam space-ch arge effects. A computer code is developed to examine the complex disp ersion relation and growth rates for the wave modes. Mode competition is considered and methods to reduce it are presented. Briggs' criteria is utilized to examine absolute and convective wave growth for the fo rward wave, backward wave, and transition mode regimes of operation as a function of the beam, hybrid mode, and slow wave grating characteri stics. An examination of the effects of beam spread on absolute and co nvective wave growth-to determine regimes for amplifier operation is c arried out. A modest Maxwellian beam spread is found to yield a regime of effective backward convective amplification, in addition to the pu rely convective growth characteristics for the forward wave mode case.