1. Nagoya University, Department of Energy Engineering and Science, Furo-cho, Nagoya 464-8603, Japan
2. National Institute for Fusion Science, Toki-shi, Gifu 509-5292, Japan
3. Kyoto University Institute of Advanced Energy, Uji-shi, Kyoto 611-0011, Japan
4. University of Tokyo Graduate School of Frontier Sciences and Graduate School Science Kashiwa-shi, Chiba 277-8561, Japan
5. General Atomics, San Diego, California 92186-5608
6. Ibaraki University, Hitachi-shi, Ibaraki 316-8511, Japan
7. Institute of Plasma Physics, Academia Sinica, Hofei 230031, China