1. The Cockcroft Institute, Keckwick Lane, Daresbury WA4 4AD, United Kingdom
2. York Plasma Institute, Department of Physics, University of York, York YO10 5DD, United Kingdom
3. Blackett Laboratory, Imperial College London, London SW7 2AZ, United Kingdom
4. The John Adams Institute for Accelerator Science, Imperial College London, London SW7 2AZ, United Kingdom
5. Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai 400005, India
6. TIFR Center for Interdisciplinary Sciences, Hyderabad 500107, India
7. Laser Plasma Section, Raja Ramanna Centre for Advanced Technology, Indore 452013, India
8. Deutsches Elektronen-Synchrotron DESY, Notkestr. 85, 22607 Hamburg, Germany
9. Center for Ultrafast Optical Science, University of Michigan, Ann Arbor, Michigan 48109-2099, USA
10. Central Laser Facility, STFC Rutherford Appleton Laboratory, Didcot OX11 0QX, United Kingdom