1. General Atomics, P.O. Box 85608, San Diego,
California 92186-5608, USA
2. École Polytechnique Fédérale de Lausanne (EPFL), Swiss Plasma Center, CH-1015 Lausanne, Switzerland
3. Massachusetts Institute of Technology, 77
Massachusetts Avenue, Cambridge, Massachusetts 02139, USA
4. Princeton Plasma Physics Laboratory, Princeton,
New Jersey 08540, USA