[1] Chinese Acad Sci, Inst Plasma Phys, HFIPS, Hefei 230031, Peoples R China
[2] Univ Sci & Technol China, Hefei 230026, Peoples R China
[3] MIT, Plasma Sci & Fus Ctr, 77 Massachusetts Ave, Cambridge, MA 02139 USA
[4] Chongqing Univ Posts & Telecommun, Chongqing 400065, Peoples R China