[1] Univ Calif Irvine, Irvine, CA 92697 USA
[2] Southwestern Inst Phys, POB 432, Chengdu 610041, Peoples R China
[3] Dalian Univ Technol, Sch Phys & Optoelect Technol, Key Lab Mat Modificat Beams, Minist Educ, Dalian 116024, Peoples R China
[4] Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England