1. Institute of Plastics Processing (IKV); RWTH Aachen University; Pontstraße 49 52062 Aachen Germany
2. Institute for Experimental Physics II; Ruhr-University Bochum; Universitätsstraße 150; 44801 Bochum Germany
3. Institute for Electrical Engineering and Plasma Technology; Ruhr-University Bochum; Universitätsstraße 150 44801 Bochum Germany