1. Laboratory of Plasma Physics and Engineering, Hokkaido University, Kita-13, Nishi-8, Kita-ku, Sapporo 060-8628, Japan
2. Hydrogen Isotope Research Center, University of Toyama, Gofuku 3190, Toyama 930-8555, Japan
3. Japan Atomic Energy Agency, 801-1 Mukouyama, Naka-shi, Ibaraki, 311-0193 Japan