Design considerations for an overmoded MW-class terahertz surface-wave oscillator

Results of theoretical and numerical simulation studies of a large cross section (overmoded), surface wave oscillator (SWO) with a cylindrical slow wave structure (SWS) are presented. The dispersion relation of the overmoded SWS, which express the phenomenon of mode competition, is calculated, and the distribution of electrical fields in the device is also determined. A novel particle in cell simulation tool is developed, aiming at the design of vacuum electron tubes in the terahertz regime. It is found that the steady-state, single-mode operation in this overmoded situation could be realized by the performance of surface wave at “π” point. Under the condition of 550kV beam voltage and 1kA beam current, 2.5D PIC simulation predicted that the proposed SWO could deliver an output power above 40 MW at the frequency of about 0.144THz with perfect time plot and fine spectrum characteristic.