Design and Fabrication of 200-GHz Oversized Surface-Wave Oscillator

A surface-wave oscillator (SWO) is one of the promising terahertz-wave sources based on excitation of a surface wave using an electron beam. The surface wave is formed by a metal periodic structure, and the frequency is determined by the size parameter of the structure and the parameters of the electron beam. In this article, we design and fabricate a 200-GHz cylindrical corrugated waveguide which has the periodic structure on the inner wall. The field intensity of the surface wave rapidly decreases to zero from the structured wall. Due to a manufacturing error of the corrugated waveguide, the frequency of the surface wave in the fabricated structure decreases to 189 GHz at π-point in comparison with the frequency of 204 GHz in the designed one. The effect of the error is evaluated by calculating the intensity distribution of the electric field of the surface wave and its growth rate due to the beam interaction. We also conduct the SWO experiment using the fabricated waveguide. Intense radiation with a total power is roughly estimated to 0.2 kW with a 45-keV and 60-A electron beam.