WT-3における強収束型準光学電子サイクロトロン加熱·電流駆動システムを用いた電流駆動実験

An 89 GHz quasi-optical Electron Cyclotron Heating (ECH)/Current Drive (ECCD) system has been installed on the WT-3 tokamak. In order to investigate the effect of localized ECH/ECCD on the MHD instabilities, this system is designed to focus the micro-wave beam into a small focal spot with the radius about 1cm in the plasma center. This radius is smaller than the inversion radius of the sawtooth oscillation observed in WT-3. Utilizing this feature, the experiment on control of sawtooth oscillation by on-axis current drive have been performed. Stabilization of sawtooth by counter-ECCD is observed when the power deposition is localized inside the inversion radius. This result may be due to the decrease in current density near the magnetic axis. For the optimal coupling of the micro-wave to obliquely propagating waves at the plasma surface, a linear-elliptical polarization converter has been installed recently. This polarization converter may raise the effective current drive efficiency by a factor of 1.5 for the injected micro-wave power.