1 Centre de Mathematiques et de Leurs Applications, ENS Cachan and CNRS, 61 Av. du President Wilson, Cachan Cedex, France
2 CEA, DIF, Arpajon Cedex, France
3 AWE plc, Aldermaston, Reading, Berkshire, United Kingdom
4 ETSI Aeronauticos, Universidad Politecnica de Madrid, Madrid, Spain
5 ELI-Beamlines, Institute of Physics, Academy of Sciences of the Czech Republic, Prague, Czech Republic