1. Institute of Plasma Physics, Chinese Academy of Sciences, P.O. Box 1126, Hefei 230031, People’s Republic of China
2. University of Science and Technology of China, Hefei 230026, People’s Republic of China
3. Forschungszentrum Jülich GmbH, Institut für Energie-und Klimaforschung–Plasmaphysik, Partner of the Trilateral Cluster (TEC), 52425 Jülich, Germany
4. Max-Planck-Institut für Plasmaphysik Teilinstitut Greifswald, Wendelsteinstr. 1, 17491 Greifswald, Germany