SINGLE-MODE AND MULTIMODE OPERATION CONDITIONS IN JINR-IAP MILLIMETER-WAVE FEL-OSCILLATOR

The influence of the Q-factor of a two-mirror Bragg resonator on the e fficiency and spectrum of radiation was studied both theoretically and experimentally for the JINR-IAP millimeter-wave free-electron laser ( FEL)-oscillator driven by a linear induction accelerator (1 MeV/200 A/ 200 ns), In accordance with theoretical predictions, single-frequency operation in a low (optimal) Q-factor resonator and multifrequency ope ration in a high Q-factor resonator were observed. For an optimal reso nator configuration at the frequency 31 GHz, single-mode generation wi th power of approximately 35 MW and efficiency of 26% was obtained. A significant drop in FEL efficiency was observed for multifrequency gen eration.