Radiation Enhancement of a Relativistic Backward-Wave Oscillator Driven by Two Annular Electron Beams

The radiation enhancement of a relativistic backward-wave oscillator (RBWO) driven by two annular electron beams is demonstrated in this paper. The slow-wave structure of RBWO is composed of a cylindrical grating with rectangular corrugation. The concentric electron beams are maintained with a velocity difference to initiate two-stream instability (TSI). The dispersion equations of the RBWO are derived and solved numerically for the growth rate of microwave signal. Compared with the single beam device, an enhancement in the growth rate is observed for the two beam case and that is attributed by the TSI. This theoretical observation is verified by 2-D particle in cell simulation and experiment. The experimental results show that the output power of 150 MW for a signal-beam device is enhanced to 200 MW for the two beam case and duration of microwave pulse is also enlarged from 10.6 to 16.8 ns. The efficiency of the devices is ~ 6%.