1. Plasma Science and Fusion Center MIT, Cambridge, Massachusetts 02139, USA
2. École Polytechnique Fédérale de Lausanne (EPFL), Swiss Plasma Center (SPC), CH-1015 Lausanne, Switzerland
3. York Plasma Institute, University of York, York, United Kingdom
4. Culham Centre for Fusion Energy, Culham Science Centre, Culham OX14 3DB, United Kingdom