Novel schemes of powerful FEM-oscillators and amplifiers for potential applications

The paper describes recent results of theoretical and experimental studies of novel schemes of FEM-oscillator and amplifiers carried out in collaboration between JINR (Dunba) and IAP RAS (N. Novgorod) based on induction linac LIU-3000 0.8 MeV / 200 A / 200 ns and aimed on topical applications, including accelerating and bio-medical applications, etc. At the present stage, efficient operation of the JINR-IAP FEM-oscillator has been demonstrated at 20 MW / 30 GHz and 5 MW / 60 GHz powers. Experimental studies of a multimegawatt power 90 GHz FEM are currently in progress. The key components of these FEMs are a short period tapered wiggler responsible for high-quality helical electron beam formation, and an advanced Bragg resonator based on coupling of propagating and quasi-cutoff waves, which improves selectivity and allows advance of the FEM into short wavelengths. To achieve a broad amplification band in the FEM-amplifier we utilized the so-called grazing incident regime, in which about of 20 MW of output power was simulated in the frequency band of 30 ± 2 GHz. During the first stage of the experiments, the designed power level and fast frequency tuning in the band 30 ± 0.5 GHz (limited by utilized input signal) have been demonstrated. According to the simulations, the use of the regime of non-resonant trapping in tapered wiggler would allow an enhance in the output power up to 35–40 MW with simultaneous widening of the amplification band. Experimental realization of this novel FEM-amplifier scheme is also currently in progress.