1. Department of Physics, University of Oxford, Parks Road, Oxford OX1 3PU, UK.
2. Centre for Fusion, Space and Astrophysics, Department of Physics, University of Warwick, Coventry CV4 7AL, UK.
3. AWE, Aldermaston, Reading, Berkshire RG7 4PR, UK.
4. LULI–CNRS, Ecole Polytechnique, CEA, Université Paris-Saclay, F-91128 Palaiseau Cedex, France.
5. Department of Physics, University of Nevada, Reno, NV 89557, USA.