[1] Univ Nevada, Dept Phys, Reno, NV 89557 USA
[2] Univ Oxford, Dept Phys, Parks Rd, Oxford OX1 3PU, England
[3] SLAC Natl Accelerator Lab, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA
[4] Queens Univ Belfast, Sch Math & Phys, Univ Rd, Belfast BT7 1NN, North Ireland
[5] STFC Rutherford Appleton Lab, Cent Laser Facil, Chilton OX11 0QX, England
[6] European XFEL, Holzkoppel 4, D-22869 Schenefeld, Germany
[7] Extreme Light Infrastruct ERIC, ELI Beamlines Facil, Radnici 835, CZ-25241 Dolni Brezany, Czech Republic
[8] Univ Alberta, Dept Elect & Comp Engn, Edmonton, AB T6G 1H9, Canada
[9] Univ Padua, Dipartimento Fis & Astron Galileo Galilei, Via F Marzolo 8, I-35131 Padua, Italy
[10] Friedrich Alexander Univ Erlangen Nurnberg, Erlangen Ctr Astroparticle Phys, Nikolaus Fiebiger Str 2, D-91058 Erlangen, Germany
[11] AWE, Reading RG7 4PR, Berks, England
[12] Univ Warwick, Ctr Fus Space & Astrophys, Dept Phys, Coventry CV4 7AL, England