1. Plasma Research Lab, Australian National University, Canberra, A.C.T. 2601, Australia
2. National Institute for Fusion Science, 322-6 Oroshi-cho, Toki 509-5292, Japan
3. Budker Institute of Nuclear Physics SB RAS, 630090 Novosibirsk, Russian Federation
4. Novosibirsk State University, 630090 Novosibirsk, Russian Federation