1. Institute for Materials Research, Tohoku University, Sendai, Japan
2. Department of Quantum Science and Energy Engineering, Tohoku University, Sendai, Japan
3. Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN
4. Hydrogen Isotope Research Center, University of Toyama, Toyama, Japan
5. Department of Helical Plasma Research, National Institute for Fusion Science, Toki, Japan
6. Institute of Advanced Energy, Kyoto University, Kyoto, Japan