1. Scottish Universities Physics Alliance SUPA, University of Strathclyde, 107 Rottenrow, Glasgow G4 0NG, UK
2. The Cockcroft Institute, Keckwick Ln, Daresbury, Warrington WA4 4AD, UK
3. Deutsches Elektronen-Synchrotron DESY, 22607 Hamburg, Germany
4. Laboratori Nazionali di Frascati, 00044 Frascati, Italy
5. Helmholtz-Zentrum Dresden-Rossendorf, Bautzner Landstraße 400, 01328 Dresden, Germany
6. Center for Advanced Systems Understanding CASUS, 02826 Görlitz, Germany
7. LOA, ENSTA Paris, CNRS, Ecole Polytechnique, Institut Polytechnique de Paris, 91762 Palaiseau, France
8. Faculty of Physics, Ludwig-Maximilians-Universität München, Am Coulombwall 1, 85748 Garching, Germany
9. Institute of Optics and Quantum Electronics, Friedrich-Schiller-University of Jena, Max-Wien-Platz 1, 07743 Jena, Germany
10. Helmholtz Institute Jena, Fröbelstieg 3, 07743 Jena, Germany
11. Max Planck Institut für Quantenoptik, Hans-Kopfermann-Straße 1, 85748 Garching, Germany
12. Center for Free Electron Science, CFEL, Luruper Chaussee 149, 22761 Hamburg, Germany