1. Chinese Academy of Sciences, Hefei Institutes of Physical Science, Institute of Plasma Physics, Hefei 230031, China
2. University of Chinese Academy of Sciences, Beijing 100049, China
3. ITER Organization, Route de Vinon-sur-Verdon, CS 90 046, 13067 St. Paul Lez Durance Cedex, France
4. Anhui University, Hefei 230601, China