Second harmonic X-mode electron cyclotron current drive (ECCD) experiments have been made in Heliotron J by using an upgraded EC launching system. A focused Gaussian beam is injected with the parallel refractive index, N||, ranging from -0.05 to 0.6. According to ray tracing calculations, the focused Gaussian beam makes the EC power absorption localized, ?p<0.2, modifying the rotational transform profile. The experimental results show that the EC driven current can be controlled by N||, and it depends on the local magnetic field structure where the EC power is deposited. A large increase in ECE signals has been observed when the EC current was driven, indicating important role of high-energy electrons on the ECCD.
Institute of Advanced Energy, Kyoto University, Gokasho, Uji, Kyoto 611, Japan Graduate School of Energy Science, Kyoto Univ., Uji, Kyoto 611-0011, Japan Kyoto Univ.Pioneering Res.Unit for Next Generation, Uji, Kyoto 611-0011, Japan National Institute for Fusion Science, Toki, Gifu 509-5292, Japan Laboratorio Nacional de Fusion, EURATOM-CIEMAT,Madrid, Spain Plasma Research Laboratory, Australian National Univ., Canberra, Australia