1. National Fusion Research Institute, Daejeon 305-333, South Korea
2. Southwest Research Institute, Texas 78238, USA
3. Institute for Physical Science and Technology, University of Maryland, College Park, Maryland 20742, USA
4. School of Space Research, Kyung Hee University, Yongin, South Korea
5. Korea Astronomy and Space Science Institute, Daejeon, South Korea
6. Department of Astronomy and Space Science, College of Natural Sciences and Institute for Basic Science Research, Chungbuk National University, Cheongju 28644, South Korea