1. School of Engineering, University of Liverpool , Liverpool L69 3BX, UK
2. Dalton Nuclear Institute, University of Manchester , 176 Oxford Rd, Manchester M13 9PL, UK
3. Nuclear Science and Technology Development Center, National Tsing Hua University , No. 101, Section 2, Guangfu Rd, East District, Hsinchu City 300, Taiwan
4. Spherical Tokamak for Energy Production (STEP), UKAEA Culham Science Centre , Abingdon OX14 3DB, Oxfordshire, UK