EXPERIMENTAL INVESTIGATION OF AN EXTERNAL FEEDBACK-SYSTEM FOR WAVELENGTH SELECTION IN A FREE-ELECTRON MASER

Results of experiments to produce high-power microwave radiation using a selective external feedback system are presented. The generator has a helical undulator and operates in the Free-Electron Maser (FEM) reg ime with an electron energy of up to 1 MeV and a total beam current of up to 1 kA. Selective feedback is achieved by reflection of radiation of given wavelength back to the FEM chamber from echelettes operating in the autocollimation regime. A growth in output signal was shown to occur in the autocollimation regime (with feedback) in two cases: wit h a small fraction of output power used as feedback and a large one wh ere the feedback and output powers were nearly equal.