Combined Resonances in Cyclotron Masers With Periodic Slow-Wave Structures

It is shown that electrons moving along helical trajectories in an external uniform magnetic field and propagating in periodic slow-wave circuits can simultaneously interact with several space harmonics of such waves. The linear theory describing combined resonances in such systems is developed. Our treatment is limited by consideration of four resonances: 1) two cyclotron resonances at the fundamental and second cyclotron harmonics; 2) the Cherenkov resonance at the zero space and zero cyclotron harmonics; and 3) the cyclotron resonance under the anomalous Doppler effect condition at the minus first cyclotron harmonic. It is shown that the growth rate and the bandwidth in the cases of such a combined resonance, in which the dominant role is, as a rule, played by the cyclotron resonance at the fundamental and the Cherenkov resonance, can be much larger than in the case of single resonances.