1. Department of Physics, University of Warwick, Coventry CV4 7AL, United Kingdom
2. Department of Physics, York Plasma Institute, University of York, York YO10 5DQ, United Kingdom
3. Central Laser Facility, STFC, Rutherford Appleton Laboratory, Harwell, Oxford OX11 0QX, United Kingdom
4. Laboratory for Laser Energetics, University of Rochester, Rochester, New York 14623-1299, USA
5. Lawrence Livermore National Laboratory, Livermore, California 94550, USA