Design of ridged waveguides for fusion energy applications

Ridged waveguides have the advantage of allowing propagation at wavelengths much longer than would otherwise be possible with a rectangular guide of the same outside dimensions. In addition, larger effective operating bandwidths are achievable. Its disadvantages are (1) larger attenuation/unit length of guide, (2) reduced power handling capabilities due to breakdown near the ridge edges, (3) more complicated field structure which does not lend itself to easy analytic formulation and (4) a hybrid TE/TM mode structure which can excite unwanted plasma modes. This paper covers design formulae for calculating waveguide cutoff, attenuation, impedance and power handling capabilities. In addition, the effect of dielectrically loading the ridged waveguide on the power handling capability and bandwidth is discussed. Specific examples are chosen from the fast wave current drive coupler requirements for PLT