1. School of Physics, Peking University 1 , Beijing 100871, China
2. Institute of Plasma Physics, Chinese Academy of Sciences 2 , Hefei 230031, China
3. Lawrence Livermore National Laboratory 3 , Livermore, California 94550, USA
4. Institute of Physics, Chinese Academy of Sciences 4 , Beijing 100190, China
5. General Atomics 5 , San Diego, California 92121, USA