1. Oden Institute for Computational Engineering and Sciences, The University of Texas at Austin, Austin, Texas 78712, USA
2. Ecole Polytechnique Fédérale de Lausanne (EPFL), Swiss Plasma Center (SPC), CH-1015 Lausanne, Switzerland
3. Institute for Fusion Studies, The University of Texas at Austin, Austin, Texas 78712, USA
4. Max-Planck-Institut für Plasmaphysik, Boltzmannstr. 2, D-85748 Garching, Germany