1. Department of Physics, York Plasma Institute, University of York, Heslington, York YO10 5DD, United Kingdom
2. Plasma Physics Group, Blackett Laboratory, Imperial College, London SW7 2BW, United Kingdom
3. Lawrence Livermore National Laboratory, 7000 East Ave., Livermore, California 94550-9234, USA
4. Max-Planck-Institute for Plasma Physics, Boltzmannstr. 2, 85748 Garching, Germany
5. Department of Physics, Chalmers University of Technology, SE-412 96 Gothenburg, Sweden
6. Science Technology and Facilities Council, Rutherford Appleton Laboratory, Harwell Campus, Didcot OX11 0QX, United Kingdom