[1] Oak Ridge Natl Lab, Oak Ridge, TN 37831 USA
[2] Gen Atom, San Diego, CA 92186 USA
[3] CEA, IRFM, F-13108 St Paul Les Durance, France
[4] DIFFER Dutch Inst Fundamental Energy Res, De Zaale 20, NL-5612 AJ Eindhoven, Netherlands
[5] Eindhoven Univ Technol, Sci & Technol Nucl Fus Grp, Eindhoven, Netherlands