1. National Fusion Research Institute, 169-148, Gwahak-ro, Yuseong-gu, Daejeon 34133, South Korea
2. Department of Physics, KAIST, 291 Daehak-ro, Yuseong-gu, Daejeon 34141, South Korea
3. National Institute of Fusion Science, 322-6 Oroshi-cho, Toki City, Gifu 509-5292, Japan