1. Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031, People's Republic of China
2. Forschungszentrum Jülich GmbH, Institut für Energie- und Klimaforschung – Plasmaphysik, Partner of the Trilateral Euregio Cluster (TEC), 52425 Jülich, Germany
3. State Key Laboratory of Advanced Electromagnetic Engineering and Technology, Huazhong University of Science and Technology, Wuhan, Hubei 430074, People's Republic of China
4. Max-Planck-Institute for Plasma Physics, 17491 Greifswald, Germany