1. Southwestern Institute of Physics, Chengdu 610041, China
2. Centre for Advanced Instrumentation, Department of Physics, Durham University, Durham DH1 3LE, United Kingdom
3. Kingdom Atomic Energy Authority, Culham Centre for Fusion Energy, Culham Science Centre, Abingdon, Oxon OX14 3DB, United Kingdom
4. University of Science and Technology of China, Hefei 230026, China
5. Australian National University, Canberra, ACT 0200, Australia