[1] EURATOM, Forschungszentrum Julich GmbH, Inst Plasma Phys, Trilateral Euregio Cluster, D-52425 Julich, Germany
[2] UKAEA Euratom Fus Assoc, Culham Sci Ctr, Abingdon OX14 3DB, Oxon, England
[3] FOM, Inst Plasmafys, Nieuwegein, Netherlands
[4] Ecole Polytech Fed Lausanne, Assoc Euratom Confederat Suisse, Ctr Rech Phys Plasmas, CH-1007 Lausanne, Switzerland