1. Southwestern Institute of Physics, P.O. Box 432, Chengdu 610041, China
2. Culham Centre for Fusion Energy, Culham Science Centre, Abingdon OX14 3DB, United Kingdom
3. Institute of Plasma Physics, Chinese Academic of Sciences, P.O. Box 1126, Hefei 230031, China
4. School of Mathematics and Statistics Science, Ludong University, Yantai 264025, China