1. Czech Technical University in Prague, Faculty of Electrical Engineering, 16627 Prague 6, Czech Republic
2. Plasma Physics Division, U.S. Naval Research Laboratory, Washington, District of Columbia 20375, USA
3. Institute of High Current Electronics SB RAS, Tomsk, 634055, Russia
4. National Research Tomsk Polytechnic University, Tomsk, 634050, Russia
5. Institute of Physics, Academy of Sciences of Czech Republic, 18221 Prague 8, Czech Republic
6. Nuclear Physics Institute, Academy of Sciences of Czech Republic, 18086 Prague, Czech Republic