1. Institut für Kernphysik, Fachbereich Physik, Technische Universität Darmstadt, D-64289 Darmstadt, Germany
2. York Plasma Institute, Department of Physics, University of York, York YO10 5DD, United Kingdom
3. Department of Physics, Scottish Universities Physics Alliance, University of Strathclyde, Glasgow G4 0NG, United Kingdom
4. Central Laser Facility, Science and Technology Facilities Council, Didcot OX11 0QX, United Kingdom