1. Alfvén Laboratory, Royal Institute of Technology, Association EURATOM-VR, 100 44 Stockholm, Sweden
2. Culham Science Centre, EURATOM / UKAEA Fusion Association, Abingdon, Oxon OX14 3DB, U K
3. School of Mathematical and Physical Sciences, Accelerator Laboratory, University of Sussex, BN1 9QH Brighton, UK
4. VTT Processes, Association EURATOM-TEKES, P.O. Box 1608, 02044 VTT, Finland