SINGLE-MODE OPERATION OF A BRAGG FREE-ELECTRON MASER OSCILLATOR

Detailed studies of the spectral characteristics and spatial mode stru cture of a single-mode, high-power Raman free-electron maser (FEM) osc illator operating with a Bragg resonator are reported. The FEM oscilla tor generated approximately 1 MW of microwave power in a single axial mode at 27.47 GHz, with an electron beam energy of 320 keV and a trans mitted current of 30 A, yielding an efficiency of 10.3%, in good agree ment with nonlinear simulations. These results indicate that a Raman f ree-electron maser can operate at high power and efficiency with stabl e single-mode output in the long pulse (equilibrium) regime.