[1] CR Frascati, Assoc Euratom ENEA Fus, I-00044 Frascati, Italy
[2] TRINITI, Troitsk 142190, Moscow Region, Russia
[3] Phys Tech Bundesanstalt, D-38116 Braunschweig, Germany
[4] Assoc Euratom UKAEA Fus, Culham Sci Ctr, Abingdon OX14 3DB, Oxon, England
[5] Assoc Euratom ENEA Fus, Consorzio RFX, I-35127 Padua, Italy