1. State Key Laboratory of Tribology, Department of Mechanical Engineering, Tsinghua University, Beijing, China
2. Institute of Plasma Physics, Chinese Academy of Sciences, Hefei, China
3. Beijing Eastforce Superconducting Technol Company Ltd, Beijing, China
4. Department of Mechinical Engineering, Adavanced Manufacturing Institute, Texas Center for Superconductivity, University of Houston, Houston, TX, USA
5. Institute of Energy, Hefei Comprehensive National Science Center and the Institute of Plasma Physics, Chinese Academy of Sciences, Hefei, China