1. Plasma Research Center, University of Tsukuba, Tsukuba 305-8577, Japan
2. Naka Fusion Institute, National Institute for Quantum and Radiological Science and Technology, Naka 311-0193, Japan
3. Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
4. National Institute for Fusion Science, Toki 509-5202, Japan
5. Institute of Advanced Energy, Kyoto University, Uji 611-0011, Japan
6. College of Engineering, Chubu University, Kasugai 487-8501, Japan
7. DIFFER-Dutch Institute for Fundamental Energy Research, Eindhoven 5612, The Netherlands