1. Karlsruhe Institute of Technology, Institute for Pulsed Power and Microwave Technology, Karlsruhe, Germany
2. Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
3. National Technical University of Athens, School of Electrical and Computer Engineering, Association EURATOM-Hellenic Republic, Athens
157 73, Greece
4. Faculty of Physics, National and Kapodistrian University of Athens, University Campus, Zografou 157 84,
Greece