1. Institute of Plasma Physics, NSC KIPT, Kharkov 61108, Ukraine
2. Laboratory for Plasma Physics - ERM/KMS, Brussels, Belgium
3. Laboratorio Nacional de Fusión Asociación Euratom/Ciemat, 28040 Madrid, Spain
4. Max-Planck-Institut für Plasmaphysik, EURATOM Assoziation, TI, D-17491, Greifswald, Germany