[1] UKAEA Euratom Fus Assoc, Culham Sci Ctr, Abingdon OX14 3DB, Oxon, England
[2] Univ Sussex, Dept Engn & Design, Brighton, E Sussex, England
[3] VTT Proc, EURATOM Assoc, Espoo 02044, Finland
[4] Max Planck Inst Plasma Phys, EURATOM Assoc, TEKES, D-85748 Garching, Germany
[5] Ecole Polytech Fed Lausanne, CRPP, CH-1015 Lausanne, Switzerland
[6] Royal Inst Technol, EURATOM Assoc, VR, S-10044 Stockholm, Sweden
[7] Princeton Univ, Plasma Phys Lab, Princeton, NJ 08543 USA