1. College of Science, Donghua University, 201620 Shanghai, People's Republic of China
2. Max-Planck-Institut für Extraterrestrische Physik, 85741 Garching, Germany
3. Institut für Theoretische Physik II: Weiche Materie, Heinrich-Heine-Universität Düsseldorf, 40225 Düsseldorf, Germany
4. Member of Magnetic Confinement Fusion Research Centre, Ministry of Education, 201620 Shanghai, People's Republic of China