1. Princeton Plasma Physics Laboratory, Princeton, New Jersey 08540, USA
2. Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
3. Consorzio RFX, Associazione Euratom-ENEA sulla fusione, C.so Stati Uniti 4, I-3512 Padova, Italy
4. Max Planck Institute for Plasma Physics, EURATOM Association, D-17491 Greifswald, Germany
5. Lodestar Research Corporation, 2400 Central Ave., Boulder, Colorado 80301, USA
6. General Atomics, P.O. Box 85608, San Diego, California 92186-5608, USA