1. Institute of Plasma Physics and Laser Microfusion, Hery 23, 01-497 Warsaw, Poland
2. Institute of Electronic Systems, Warsaw University of Technology, Nowowiejska 15/19, 00-665 Warsaw, Poland
3. Max Planck Institute for Plasma Physics, Boltzmannstr. 2, 85748 Garching, Germany
4. CEA, IRFM, F-13108 Saint-Paul-lez-Durance, France