1. Max Planck Institute for Solar System Research, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany
2. Max Planck/Princeton Center for Plasma Physics, Boltzmannstraβe 2, 85748 Garching, Germany
3. Max Planck Institute for Plasma Physics, Wendelsteinstr. 1, 17491 Greifswald, Germany