1. Key Laboratory of Materials Modification by Beams of the Ministry of Education, School of Physics, Dalian University of Technology, Dalian 116024, People's Republic of China
2. National Fusion Research Institute, Daejeon 169-148, South Korea
3. Department of Nuclear Engineering, Seoul National University, Seoul 151-742, South Korea
4. Southwestern Institute of Physics, Chengdu 610041, People's Republic of China
5. Institute for Fusion Theory and Simulation, Zhejiang University, Hangzhou 310027, People's Republic of China