1. Department of Quantum Science and Energy Engineering, Tohoku University, Sendai 980-8579, Japan
2. Research Institute for Applied Mechanics Kyushu University, 6-1 Kasuga-kouen, Kasuga, Fukuoka 816-8580, Japan
3. Akita Prefectural University, Honjyo, Akita 015-0055, Japan
4. National Institute for Fusion Science, 322-6 Oroshi-cho, Toki 509-5292, Japan