1. National Institutes of Natural Sciences, National Institute for Fusion Science, Toki 509-5292, Japan
2. SOKENDAI (The Graduate University for Advanced Study), 322-6 Oroshi, Toki-city 509-5292, Japan
3. Research Institute for Applied Mechanics, Kyushu University, Kasuga 816-8580, Japan
4. Department of Energy Engineering and Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8601, Japan
5. Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa 277-8561, Japan
6. Research Center for Development of Far-Infrared Region, University of Fukui, Bunkyo 3-9-1, Fukui 910-8507, Japan