Design and Theoretical Modeling of a Two-Section X-Band BWO With Intermediate Drift Space for Efficient Low Magnetic Field Operation

A two-section X-band backward wave oscillator (BWO) employing a trapezoidal slow wave structure (SWS), segmented by an analytically modeled intermediate drift space, is proposed for efficient low magnetic field operation. The drift space, introduced between the two SWS sections, is theoretically optimized to enhance phase correlation between the electron beam and RF wave, reaching the second SWS (SWS2). This enables a more effective beam–wave interaction in the second section, contributing toward improved energy conversion. The sectioning of the SWS allows clear separation between the beam modulation region and the energy exchange region, while the drift space provides a feedback mechanism that reinforces stronger velocity modulation at the first SWS (SWS1). The drift length is estimated analytically and validated through a full 3-D particle-in-cell (PIC) simulation. A more compact beam bunching is observed in phase space, resulting in a simulated microwave conversion efficiency of 50% at 410 kV, 4.72 kA, with a guiding magnetic field of 0.5 T. The electronic efficiency, observed from the power lost in the collector, corroborates the simulated power conversion efficiency.