Controlled amplification in a relativistic resonant TWT by varying the guide magnetic field

We demonstrate how the zone of cyclotron suppression of generation in a resonant TWT can be exploited to amplify an external signal. The appearance of a stop-band, when a resonant interaction of a fast cyclotron wave of the electron beam with a counter-propagating electromagnetic wave takes place, determines the absorption of the reflected electromagnetic wave from the output end of the interaction space. As one adjusts the value of the guide magnetic field from its resonant value to the boundaries of the zone of cyclotron absorption, which represent the threshold of self-excitation, we observe an increase in the amplitude of the reflected wave, which is responsible for positive feedback, on the input end of the interaction space. The result is in increased regenerative amplification.