[1] UKAEA United Kingdom Atom Energy Author, Culham Sci Ctr, Abingdon OX14 3DB, Oxon, England
[2] Swansea Univ, Coll Engn, Bay Campus, Swansea SA1 8EN, W Glam, Wales
[3] Rutherford Appleton Lab, STFC, ISIS Facil, Harwell OX11 0QX, Berks, England
[4] Max Planck Inst Plasma Phys, Boltzmann Str 2, D-85748 Garching, Germany