1. Center for Magnetic Fusion Theory, CAS, Hefei, Anhui 230026, China
2. Department of Modern Physics, University of Science and Technology of China, Hefei, Anhui 230026, China
3. School of Science, Sichuan University of Science and Engineering, Zigong, Sichuan 643000, China
4. Institute for Fusion Studies, University of Texas at Austin, Austin, Texas 78712, USA