MoS2-Schmierung für hochbelastete Stützelemente zwischen supraleitenden Magnetspulen

The magnetic plasma confinement system of the nuclear fusion experiment Wendelstein 7-X, which is currently under construction, consists of 20 planar and 50 non-planar superconducting coils. The casings of these coils have contact through Narrow Support Elements (NSEs), consisting of Al-bronze pads with convex surfaces and flat stainless-steel counter-faces. When the magnetic field is ramped up, forces up to 1500 kN and tangential sliding motion of some mm occur. Because mechanical disturbances may cause quenching of the superconducting magnets, only low friction without any stick-slip behaviour is tolerable. The NSEs are operated in high vacuum at a temperature of about 4 K. Thusg only dry sliding tribosystems are applicable. In pre-tests a PVD-MoS 2 -coating had proven to be the optimum solution. This coating was tested on downsized samples, in reciprocating motion, in liquid nitrogen (T = 77 K) and liquid helium (T = 4.2 K). The counter-bodies were coated by a spray-deposited MoS 2 -film. In long-term tests with up to 14900 friction cycles in liquid nitrogen, this combination showed stable stick-slip free sliding behaviour without coating failure. However, tests in liquid helium showed a distinct stick-slip effect, whose origin has not been clarified so far.