1. Fusion Simulation Center, State Key Laboratory of Nuclear Physics and Technology, School of Physics, Peking University, Beijing 100871, China
2. Department of Physics and Astronomy, University of California, Irvine, California 92697, USA
3. Institute for Fusion Theory and Simulation, Zhejiang University, Hangzhou 310027, China
4. General Atomics, P.O. Box 85608, San Diego, California 92186-5608, USA