1. Institute of Physics, Czech Academy of Sciences, Na Slovance 2, Prague 8 18221, Czech Republic
2. Institute of Plasma Physics, Czech Academy of Sciences, Za Slovankou 3, 182 00 Prague 8, Czech Republic
3. Deutsches Elektronen-Synchrotron DESY, Notkestraße 85, 22607 Hamburg, Germany
4. Center of Free-Electron Laser Science CFEL, Deutsches Elektronen-Synchrotron DESY, 22607 Hamburg, Germany
5. Institute of Nuclear Physics, Polish Academy of Sciences, Radzikowskiego 152, 31-342 Krakow, Poland