1. Plasma Technology Research Center, National Fusion Research Institute, 814-2, Osikdo-dong, Gunsan, Jeollabuk-do 54004, South Korea
2. Department of Physics, Chungnam National University, Daejeon 34134, South Korea
3. Faculty of Physics, Astronomy and Applied Informatics, University Nicolaus Copernicus, Grudziadzka 5, 87-100 Toruń, Poland
4. Department of Physics, University of Central Florida, Orlando, Florida 32816, USA
5. Faculty of Science and Technology, Keio University (Retired), 3-14-1 Hiyoshi, Yokohama 223-8522, Japan
6. Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, United Kingdom