1. Department of Electrical and Electronic Systems; Saitama University; Sakura-ku Saitama 338-8570 Japan
2. Plasma Research Center, University of Tsukuba; Tsukuba Ibaraki 305-8577 Japan
3. National Institute for Fusion Science; Toki 509-5292 Japan
4. Department of Mechanical Systems Engineering; Tokyo University of Agriculture and Technology; Koganei Tokyo 184-8588 Japan
5. Global Innovation Center, Kyushu University; Kasuga-shi Fukuoka 816-8580 Japan
6. Electronics Research Institute, Fukuoka Institute of Technology; Higashi Ward Fukuoka 811-0214 Japan