1. State Key Laboratory of Nuclear Physics and Technology, Peking University, Beijing 100871, China
2. Dipartimento di Fisica, Università di Milano-Bicocca, Milano 20126, Italy
3. China Academy of Engineering Physics, Mianyang 621900, China
4. China Institute of Atomic Energy, Beijing 102413, China
5. National Institute of Metrology, Beijing 100029, China
6. Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031, China