A Ridged Waveguide Slotted Coupler for Large Tokamaks

A new ridged waveguide slotted coupler is proposed for large tokamaks and its promising characteristics are pointed out experimentally. A short circuit attached to the end of a ridged waveguide and a series of slots to cover the mouth launch the ion-cyclotron range of frequencies (ICRF) waves into the plasma with electric field orthogonal to the main toroidal magnetic field. The simulated experiment using water instead of the plasma load showed that the voltage standing-wave ratio (VSWR) in one typical guide is 3.0 and 5.0 for the distance to water being 0.02 λ0 and 0.04 λ0, respectively. The matching section inserted into the coupler reduces its VSWR to less than one-third.