A large-signal beam-wave interaction code for folded-waveguide traveling-wave tubes is presented. Formulation in frequency domain yields fast results of the steady state. The slow-wave structure is described by an equivalent circuit, while the electrons of the beam are modeled by means of a particle-in-cell approach. The latter exploits the periodicity of the electromagnetic fields in the beam tunnel region, thus allowing to work with a relatively low number of injected particles compared to conventional implementations. Physically consistent solutions are then obtained iteratively by incorporating the well-established Broyden's method. Further improvement in terms of computation time is achieved by initializing the iterative algorithm with results from previous simulations. The approach is verified by a comparison with published interaction simulation results. Single-frequency responses are obtained within a few minutes, which compares favorably with other specialized simulation packages and enables device optimization with acceptable effort.
