1. Department of Applied Quantum Physics and Nuclear Engineering, Graduate School of Engineering, Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan
2. Naka Fusion Research Establishment, Japan Atomic Energy Research Institute 801-1 Mukouyama, Naka-machi, Naka-gun, Ibaraki, 311-0193, Japan