Non-uniform guiding magnetic field for efficiency enhancement of RBWO

Abstract

Relativistic backward wave oscillator (RBWO) having a resonant reflector and slow wave structure (SWS) combination has been simulated for a 400 kV peak accelerating voltage and a 4.0 kA peak electron beam current. The particle in cell simulations predict an electron beam to microwave conversion efficiency of 44% at a 3.22 GHz operating frequency. Phase space plot analysis reveals that the backstreaming of electrons from the end reflector and the end part of SWS affects the device efficiency. It was demonstrated using particles in cell simulations that with non-uniform guiding magnetic field, these backstreaming electrons do not attain synchronism with the forward wave while drifting toward the anode end and eventually rebound from the anode–cathode gap. Backstreaming of electrons reduces with increasing non-uniformity in the magnetic field. These two phenomena result in a significant enhancement in the output microwave power at a 3.22 GHz frequency and device efficiency enhances to a level of 62%. With the proposed guiding magnetic field profile, RBWO retains a larger than 52% electron beam to microwave conversion efficiency with the nominal accelerating voltage anywhere in between 400 and 600 kV and an electron beam current of 3.9–7.2 kA.