1. SuperOx Japan LLC 1 , Tokyo 252-0243, Japan
2. ISIS, STFC, Rutherford Appleton Laboratory, Harwell Science and Innovation Campus 2 , Didcot, OX11 0QX, United Kingdom
3. Department of Physics, The University of Warwick 3 , Gibbet Hill Road, Coventry, CV4 7AL, United Kingdom
4. UKAEA CCFE, Culham Science Centre 4 , Abingdon OX14 3DB, United Kingdom