Acoustic monitoring of superconducting magnet component test and shock simulation of coils

Abstract Monitoring of critical components is becoming a more and more important task especially in complex multidisciplinary systems as e.g. the Wendelstein 7-X [L. Wegener et al., Status of Wendelstein 7-X construction, Fusion Engineering and Design, in press; M. Gasparotto et al., The Wendelstein 7-X mechanical structure support elements, Fusion Engineering and Design 74 (2005) 161]. Here especially the superconducting magnetic coil system – comprising, i.a., narrow support elements (NSEs) and bolted connections – is considered. These had been tested in a full-scale test set-up with multi axial loading in the MN range at 77 K and vacuum [B. Heinemann et al., Design of narrow support elements for non planar coils of Wendelstein 7-X, 21st IEEE/NPSS Symposium on Fusion Engineering (SOFE05), Knoxville/USA, 26–9 September 2005, paper 078; D. Hathiramani et al., Full-scale friction test on tilted sliding bearings for Wendelstein 7-X coils, Fusion Engineering and Design, in press]. A smooth sliding of coated surfaces is a major requirement, as non-smooth sliding (stick-slip) excites high mechanical shock loads, which may cause a quench of the superconductor. For an early detection of stick-slip an acoustic monitoring system has been developed and installed. Three sensor types have been compared and data analysis procedures have been developed. It has been shown that acoustic monitoring is possible under such environmental conditions at complex test set-ups and is complementary to standard sensor systems. For the development of the mechanical quench experiment, in which the actual quench sensitivityl to mechanical shock loads is investigated by impact loads, numerical simulations have been performed. For this a semi-analytical model employing a reduced modal state space model of the coil and Hertz’ian theory for the contact formulation has been set-up. Based on experimental and numerical verification it proved to be an appropriate and efficient tool for simulating complex mechanical systems under transient dynamic loading. Finally, a statistical energy based model has been set-up for simulating the propagation of stick-slip shocks within the complex coil system. Concluding, with the developed acoustic monitoring as well as the numerical simulation models two valuable tools for the W7-X development-test projects have been developed.