1. G.V. Kurdyumov Institute for Metal Physics, NAS of Ukraine, 36 Academician Vernadsky Blvd., UA-03680 Kyiv-142, Ukraine
2. Troitsk Institute of Innovative and Thermonuclear Research, 12 Pushkovykh Str., Troitsk, Russia
3. Lomonosov Moscow State University, 1 Leninskie Gory, 119991 Moscow, Russia