TRAVELING-WAVE ANTENNA FOR FAST-WAVE HEATING AND CURRENT DRIVE IN TOKAMAKS

The traveling-wave antenna for heating and current drive in the ion cy clotron range of frequencies is shown theoretically to have loading an d wavenumber spectra that are largely independent of plasma conditions . These characteristics have been demonstrated in low-power experiment s on the DIII-D tokamak, in which a standard four-strap antenna was co nverted to a traveling-wave antenna through use of external coupling e lements. The experiments indicate that the array maintains good impeda nce matching without dynamic tuning during abrupt changes in the plasm a, such as during L- to H-mode transitions, edge-localized mode activi ty, and disruptions. An analytic model was developed that exhibits the features observed in the experiments. Guidelines for the design of tr aveling-wave antennas are derived from the validated model.