1. Max-Planck-Institut für Plasmaphysik EURATOM Association, D-17491 Greifswald, Germany
2. National Institute for Fusion Science Toki-shi, Gifu-ken 509-5292, Japan
3. Oak Ridge National Laboratory, P.O. Box 2008, M.S. 6169, Oak Ridge, Tennessee 37831
4. Kyoto University, Institute of Advanced Energy, Gakasho, Uji, Japan