1. Princeton Plasma Physics Laboratory 1 , Princeton, New Jersey 08543-0451, USA
2. General Atomics 2 , P.O. Box 85608, San Diego, California 92186-5608, USA
3. Max-Plank-Institut fur Plasmaphysik 3 , 85748 Garching, Germany
4. The University of Texas at Austin 4 , Austin, Texas 78712, USA
5. Massachusetts Institute of Technology 5 , Cambridge, Massachusetts 02139, USA
6. University of Wisconsin-Madison 6 , Madison, Wisconsin 53706, USA
7. University of California at Davis 7 , Davis, California 95616, USA