1. Science Institute, University of Iceland, Dunhaga 3, IS-107 Reykjavik, Iceland
2. Laboratoire de Physique des Gaz et Plasmas—LPGP, UMR 8578 CNRS, Université Paris-Sud, Université Paris Saclay, 91405 Orsay CEDEX, France
3. Institute of Physics v. v. i., Academy of Sciences of the Czech Republic, Na Slovance 2, 182 21 Prague 8, Czech Republic
4. Department of Space and Plasma Physics, School of Electrical Engineering and Computer Science, KTH Royal Institute of Technology, SE-100 44 Stockholm, Sweden
5. Plasma and Coatings Physics Division, IFM-Materials Physics, Linköping University, SE-581 83 Linköping, Sweden