1. Forschungszentrum Jülich GmbH, Institute for Advanced Simulation, Jülich Supercomputing Centre D-52425 Jülich, Germany
2. Max Born Institute, Max Born Str. 2a, D-12489 Berlin, Germany
3. Centre for Mathematical Plasma Astrophysics, Department of Mathematics, KU Leuven, Celestijnenlaan 200B, 3001 Heverlee, Belgium