Institute of Plasma Physics;
Chinese Academy of Sciences;
Hefei 230031;
China;
Science Island Branch of Graduate School;
University of Science and Technology of China;
Hefei 230031;
China;
Department of Modern Physics;
University of Science and Technology of China;
Hefei 230026;
China;
Center for Magnetic Fusion Theory;
Chinese Academy of Sciences;
Hefei 230031;
China;
Plasma Physics Laboratory;
Princeton University;
Princeton;
NJ 08543;
USA;