1. Key Laboratory of Materials Modification by Laser, Ion and Electron Beams (Ministry of Education), School of Physics, Dalian University of Technology, Dalian 116024, China
2. Institute for Fusion Theory and Simulation and Department of Physics, Zhejiang University, Hangzhou, Zhejiang 310027, China
3. General Atomics, P.O. Box 85608, San Diego, California 92186-5608, USA
4. Princeton Plasma Physics Laboratory, 100 Stellarator Rd., Princeton, New Jersey 08540, USA
5. Columbia University, 2960 Broadway, New York, New York 10027-6900, USA