1. Department of Physics and Astronomy, University of Exeter, Stocker Road, Exeter, Devon EX4 4QL, U.K.
2. Diamond Light Source, Harwell Science and Innovation Campus, Didcot OX11 0DE, U.K.
3. Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
4. Cornell High Energy Synchrotron Source, Cornell University, Ithaca, New York 14853, United States
5. School of Physics and Astronomy, University of Southampton, Southampton SO17 1BJ, U.K.
6. Department of Physics, Clarendon Laboratory, University of Oxford, Oxford OX1 3PU, U.K.
7. College of Engineering, Mathematics and Physical Sciences, University of Exeter, Stocker Road, Exeter, Devon EX4 4QL, U.K.