Effective co-generation of opposite and forward waves in cyclotron-resonance masers

A novel type of the frequency-tunable oscillator based on simultaneous gene ration of the forward and opposite waves at the same frequency, but at diff erent cyclotron harmonics, is proposed. A spatially periodic helical electr on beam allows for strong coupling of the waves. The opposite wave provides the broadband feedback and electron bunching, whereas the forward wave amp lifies the arising signal and withdraws the rf power from the interaction r egion. A 15% efficiency and 5% frequency bandwidth have been achieved in th e first experiment.