1. Rudolf Peierls Centre for Theoretical Physics, University of Oxford, Oxford OX1 3NP, United Kingdom
2. Massachusetts Institute of Technology (MIT), Cambridge, Massachusetts 02139, USA
3. Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543, USA
4. General Atomics, P.O. Box 85608, San Diego, California 92186, USA
5. University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
6. Center for Energy Research, University of California-San Diego (UCSD), La Jolla, California 92093-0417, USA
7. University of California at Davis, Davis, California 95616, USA