1. National Institute for Fusion Science, Toki 509-5292, Japan
2. Department of Quantum Science and Energy Engineering, Tohoku University, Sendai 980-8579, Japan
3. Interdisciplinary Graduate School of Engineering Science, Kyushu University, Kasuga 816-8580, Japan
4. Department of Electrical Engineering and Computer Science, Nagoya University, Nagoya 464-8603, Japan