Measurements of Gain for Slow Cyclotron Waves on an Annular Electron Beam

Gain was measured for fast and slow waves propagating in a dielectric-loaded T${\mathrm{E}}_{01}$ axi-symmetric waveguide penetrated by an annular electron beam. This measurement is the first reported in the slow-wave regime, where axial velocity modulation dominates the azimuthal bunching. Small-signal gain at 6.0 GHz of over 30 dB, instantaneous bandwidth of 3.7%, and tuning bandwidth of over 11% are reported. In a feedback-amplifier configuration gain of 53 dB, power output of 20 kW, and 10% electronic efficiency are also reported.