1. Research Institute for Applied Mechanics, Kyushu University, Kasuga, Fukuoka 816-8580
2. Interdisciplinary Graduate School of Engineering Science, Kyushu University, Kasuga, Fukuoka 816-8580
3. Uji, Kyoto 611-001
4. National Institute for Fusion Science, Toki, Gifu 509-5292
5. Center for Energy Research, University of California, San Diego, La Jolla, CA 92093-0417, U.S.A.
6. Center for Astrophysics and Space Sciences, University of California, San Diego, La Jolla, CA 92093-0424, U.S.A.
7. Graduate School of Frontier Science, University of Tokyo, Kashiwa, Chiba 509-5292