1 Nevada Terawatt Facility, Physics Department, MS-220, University of Nevada, Reno, Nevada 89557, USA
2 Laboratoire pour l'Utilisation des Lasers Intenses, UMR 7605 CNRS-CEA-Ecole Polytechnique-Universite Paris VI, 91128 Palaiseau, France
3 Centre de Physique Thdorique, UMR 7644 CNRS-Ecole Polytechnique, 91128 Palaiseau, France
4 Heinrich Heine Universitat Dusseldorf, D-40225 Dusseldorf, Germany
5 School of Mathematics and Physics, The Queen's University Belfast, Belfast BT7 1NN, Northern Ireland, United Kingdom
6 DPTA, CEA-DIF, Bruyeres-le-Chatel, France