1. Faculty of Engineering, Tottori University, Minami 4-101, Koyama-cho, Tottori-shi, Tottori 680-8552, Japan
2. Physics Department and Institute for Fusion Studies, University of Texas at Austin, Austin, Texas 78712, USA
3. National Institute for Fusion Science, 322-6 Oroshi-cho, Toki 509-5292, Japan
4. SOKENDAI, The Graduate University for Advanced Studies, Toki 509-5292, Japan