Analysis of Field Variation in Low Magnetic Field Regime among RBWOs

Over the past few decades, operating backward wave oscillators (BWOs) at low magnetic field has gained priority because of many benefits and difficulties encountered during the operation. Key challenges included cyclotron resonances and poor beam quality, manifested as larger Larmour radius leading to secondary emission. This paper examines the impact of varying the guiding magnetic field up to the cyclotron resonance value on essential BWO parameters, including output power, frequency, and beam current. Three variants of BWO based on slow wave structure (SWS) geometry, having different interaction impedance at beam position, have been designed and simulated under the aforementioned condition. Also, the simulated parameters are compared with the estimated design parameters. The simulation has been performed using CST Microwave studio and efficiency was observed for different magnetic fields. Additionally, the phase space plots corresponding to those magnetic fields where the output power is maximum and minimum, are shown in this paper to understand the beam modulation near cyclotron resonance field.