Relativistic gyrotrons with highly selective resonators for transverse magnetic modes

The efficiency of relativistic gyrotrons with transverse-magnetic-mode echelette resonators is experimentally demonstrated. It is shown that it is possible to devise a resonator with a single high-Q mode with azimuthal index m = 1 and longitudinal index q = 1 by choosing appropriate dimensions and diameters of the recesses in the echelette resonator. It is concluded that high radiation powers were achieved in the spectral region of 2.8-4.0 mm; at a current of 2 kA, for example, the maximum radiation power was 20-30 MW, and at a current of 6-7 kA a power of 20-30 MW and efficiency of up to 1 percent were attained.