1. Institute of Fusion Science, School of Physical Science and Technology, Southwest Jiaotong University, Chengdu 610031, Sichuan, People's Republic of China
2. Laboratoire de Physique des Plasmas-Laboratorium voor Plasmafysica, Ecole Royale Militaire-Koninklijke Militaire School, Trilateral Euregio Cluster, B-1000 Brussels, Belgium
3. Institute of Energy and Climate Research-Plasma Physics, Forschungszentrum Jülich GmbH, Association EURATOM-FZJ, Trilateral Euregio Cluster, D-52425 Jülich, Germany