1. Institute of Plasma Physics, HFIPS, Chinese Academy of Sciences, Hefei 230031, PR China
2. University of Science and Technology of China, Hefei 230026, PR China
3. Institute of Materials, China Academy of Engineering Physics, Mianyang 621907, PR China
4. School of Electrical Engineering, Southwest Jiaotong University, Chengdu 611756, China
5. School of Physical Science and Technology, Xinjiang University, Urumqi 830046, China