1. State Key Laboratory of Nuclear Physics and Technology, School of Physics, Peking University, Beijing 100871, China
2. Dipartimento di Fisica “G. Occhialini,” Università degli Studi di Milano-Bicocca, Milano 20126, Italy
3. Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031, Anhui, China
4. Institute for Plasma Science and Technology, National Research Council, Milan 20125, Italy