High-power broadband 30-GHz FEM amplifier operated in the grazing incident regime

A high-power broadband free electron maser (FEM) amplifier has been realized in collaboration between JINR (Dubna) and IAP RAS (Nizhny Novgorod) based on the linac LIU-3000 (0.8 MeV/200 A/250 ns). To achieve a wide frequency amplification band, the regime characterized by grazing of the dispersion curves of the beam electrons to the operating wave (the so-called grazing regime) was studied in the FEM. According to the simulations, such an operating regime allows an instant amplification band of up to 5%–7% with output power at the level ∼20 MW and a gain of about 30–35 dB to be obtained in the Ka band. The proof-of-principle experiments examined this scheme in the 30-GHz frequency range and confirmed the simulations. As a result, the predicted power level with design parameters has been achieved, and fast frequency tuning within the feeding magnetron band ±0.5 GHz has been demonstrated.