Amplitude locking in a gyroTWT amplifier with a delayed feedback

Summary form only given, as follows. Enhanced pulsed output is observed in a delayed-feedback gyroTWT amplifier. The gyroTWT consists of a rectangular WR90 waveguide divided to three stages of amplification. The first and third stages are loss-less, in order to enhance electron-bunching and output power, respectively, while the second stage has distribution wall losses in order to prevent backward-wave instabilities. A low-voltage low-current electron-beam (18 kV, 0.3 A) interacts with the EM wave. An external 60 ns delay line operating as a feedback couples the output power to the RF input port, through a set of isolators, attenuators, and a fast RF switch. The closed-loop gain is slightly above unity. The switch is modulated externally at a frequency rate inversely proportional to the feedback loop delay time. The experimental observations are supported by a time-dependent numerical computations.