Simulation of 0.34THz Backward Wave Oscillator with Cylindrical Beam and Sheet Beam

The nonlinear RF performances of a planarstructured 0.34 THz BWO with the cylindrical electron beam, as well as with the equivalent sheet electron beam, were successfully analyzed using in-house developed one-dimensional large-signal model (SUNRAY-1D). The cylindrical beam and the equivalent sheet beam were chosen for the same beam voltage, the same beam current, and the same cross-sectional area. The variation of the BWO output power and the BWO oscillating frequency with varying beam voltage were simulated. It was found that the simulated output power of the BWO with the sheet beam is at least twice that of the BWO with the equivalent cylindrical beam over the full tuning range. This was due to relatively higher values of the interaction impedance and a relatively lower space charge field for the sheet beam compared to that for the equivalent cylindrical beam. The simulated output power and the tuning range of the 0.34 THz BWO using the SUNRAY model were found to be comparable with the published RF performance of the BWO as simulated by the CST-3D particle-in-cell 3d e.m. simulation code for different input beam voltages. The major advantage of the SUNRAY code is that it takes much less than a minute to simulate BWO output power at one frequency, and can therefore be used interactively for the initial design of a BWO.