1. GREMI, University of Orliéans, 45067 Orléans cedex 2, France
2. Kurchatov Institute, 123182 Moscow, Russia
3. Institute of Plasma Physics, 182 11 Prague, Czech Republic
4. Jagiellonian University, Reymonta 4, 30-059 Cracow, Poland
5. Technical University, 616 69 Brno, Czech Republic