1. International Joint Research Laboratory of Magnetic Confinement Fusion and Plasma Physics, State Key Laboratory of Advanced Electromagnetic Engineering and Technology, School of Electrical and Electronic Engineering, Huazhong University of Science and Technology, Wuhan 430074, China
2. University of California, Davis, California 95616, USA
3. Department of Modern Physics, School of Physical Sciences, University of Science and Technology of China, Hefei, Anhui 230026, China