Gyro-Traveling Wave Amplifier

The theory, design and experimental results of a wideband 140 GHz, 1 kW pulsed gyro-traveling wave amplifier are presented. The gyro-TWA operates in the HE(0,6) mode of an overmoded quasi-optical waveguide using a gyrating electron beam. The electromagnetic theory, interaction theory, design processes and experimental procedures are described in detail. At 37.7 kV and 2.7 A beam current, the experiment has produced over 820 W peak power with a -3 dB bandwidth of 0.8 GHz, and a linear gain of 34 dB at 34.7 kV. In addition, the amplifier produced a -3 dB bandwidth of over 1.5 GHz (1.1%) with a peak power of 570 W from a 38.5 kV, 2.5 A electron beam. The electron beam is estimated to have a pitch factor of 0.55 to 0.6, radius of 1.9 mm and calculated perpendicular momentum spread of approximately 9%. The gyro-amplifier was nominally operated at a pulse length of 2 microseconds, but was tested to amplify pulses as short as 4 nanoseconds with no noticeable pulse broadening. Internal reflections in the amplifier were identified using these short pulses by time-domain reflectometry. The demonstrated performance of this amplifier shows that it can be applied to Dynamic Nuclear Polarization (DNP) and Electron Paramagnetic Resonance (EPR) spectroscopy. Index Terms gyro-amplifier, gyro-twt, confocal.