1. Institute of Plasma Physics, Chinese Academy of Science, Hefei, Anhui 230031, China
2. General Atomics, P. O. Box 85608, San Diego, California 92186-5608, USA
3. Lawrence Livermore National Laboratory, Livermore, California 94551, USA
4. Department of Engineering Physics, University of Wisconsin-Madison, 1500 Engineering Drive, Madison, Wisconsin 53706-1609, USA
5. Princeton Plasma Physics Laboratory, PO Box 451, Princeton, New Jersey 08543-0451, USA
6. Center for Energy Research, University of California San Diego, 9500 Gilman Dr., La Jolla, CA 92093-0417, USA