Design of an overmoded MW-class terahertz backward wave oscillator

Results of the theoretical and numerical simulation studies of a mega watt, large diameter terahertz backward wave oscillator are presented in this paper. The device consists of a large cross-section (overmoded), slow wave structure (SWS) with a unique profile of wall radius specifically designed to support surface wave and to provide a strong beam-wave coupling at moderate voltage. The Particle-in-cell simulation method is used to study the effects of device parameters which are critical to the optimization of output power in a prototype 0.14 THz backward wave oscillator. Numerical results demonstrate that both the total length of SWS and length of back drift tube affect the output power remarkably, while the slot width is responsible for mode transformation. It is also found that the steady-state, single-frequency operation in this overmoded situation could be realized by the characteristic of surface wave near upper cutoff point.