FEL´s with Bragg reflection resonators: Cyclotron autoresonance masers versus ubitrons

FEL´s based on the stimulated undulator radiation (ubitrons) are compared with those based on the stimulated cyclotron radiation [cyclotron autoresonance masers (CARM´s)]. If the high-current accelerators are used as electron injectors, then from the viewpoint of simplicity of oscillatory electron energy pumping, criticality with respect to electron velocity dispersion, and efficiency, CARM´s seem to be more effective than ubitrons at mm and sbmm waves. For such HF generators, resonators based on selective Bragg reflection of electromagnetic waves in corrugated metallic tubes are most atractive. CARM´s of this type yield 6 MW at a 4 mm wavelength and 10 MW at a 2 mm wavelength in the single-mode regime.