1. SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA
2. University of Michigan, Ann Arbor, Michigan 48109, USA
3. European XFEL GmbH, Holzkoppel 4, D-22869 Schenefeld, Germany
4. Helmholtz-Zentrum Dresden-Rossendorf, 01328 Dresden, Germany
5. Lawrence Livermore National Laboratory, Livermore, California 94550, USA