1. National Institute for Natural Sciences, National Institute for Fusion Science, 322-6 Oroshi, Toki 509-5292, Japan
2. The Graduate University for Advanced Studies, Department of Fusion Science, (SOKENDAI), 322-6 Oroshi Toki 509-5292, Japan
3. Princeton Plasma Physics Laboratory, P.O. Box 451, Princeton, New Jersey 08543
4. University of Wisconsin-Madison, Department of Engineering Physics, Madison, Wisconsin 53706