A Polarization-Converted Coupler for the Fast-Wave Current Drive

This paper proposes a new type of waveguide coupler for the fast-wave current drive in large tokamaks. The coupler has a narrow width to be arrayed in the toroidal direction for the phasing, and radiates the electric field perpendicular to the main toroidal magnetic field through the Faraday shield. The coupler consists of tuned posts or ridges in the cutoff cavity and triangle-shaped waveguides inside the rectangular waveguide. Model experiments verify its basic characteristics, and theoretical estimates indicate that the polarization-converted coupler has the power capability in the range of megawatts.