Southwestern Institute of Physics;
Chengdu 610041;
China;
Laboratory of Plasma Physics and Engineering;
Hokkaido University;
Kita-13;
Nishi-8;
Kita-ku;
Sapporo 060-8628;
Japan;
National Institute for Fusion Science;
Toki-shi;
Gifu-ken 509-5202;
Japan;