1. School of Nuclear Science and Technology, Lanzhou University, Lanzhou 730000, China
2. Department of Electrical and Electronic Engineering, Faculty of Engineering, Utsunomiya University, Yoto 7-1-2, Utsunomiya, Tochigi 321-8585, Japan
3. Center for Optical Research and Education (CORE), Utsunomiya University, Yoto 7-1-2, Utsunomiya, Tochigi 321-8585, Japan
4. Graduate School of Science and Engineering for Research, University of Toyama, Toyama, Toyama 930-8555, Japan
5. Department of Electrical Engineering, Nagaoka University of Technology, Kami-tomiokamachi 1603-1, Nagaoka, Niigata 940-2188, Japan
6. Institute of Applied Physics, University of Tsukuba, Tsukuba, Ibaraki 305-8573, Japan
7. National Institute for Fusion Science (NIFS), Toki, Gifu 509-5292, Japan
8. Department of Fusion Science, SOKENDAI (The Graduate University of Advanced Studies), Toki, Gifu 509-5292, Japan
9. School of Physics, University College Dublin, Belfield, Dublin 4, Ireland