Abstract
We have directly measured, for the first time, the Nb3Sn and Cu loading strains and stresses in 11 T dipole coil segments upon compressive loading using neutron diffraction. For this purpose a load frame that enables rotation of the sample load axis with respect to the neutron scattering geometry was installed in the Stress-Spec beamline at the Heinz Maier-Leibnitz FRM II neutron source. The neutron diffraction data suggests that the magnet coil wound of Rutherford type cables can be considered as a fibre reinforced composite material. In the axial load direction the load is mainly carried by the Nb3Sn filaments and the composite stiffness can be estimated by the rule of mixtures assuming iso-strain conditions in all composite constituents. Under transverse compression the fully annealed Cu provides an isotropic pressure around the Nb3Sn filaments. The transverse load stresses in the Cu and Nb3Sn are similar, indicating iso-stress behaviour of the coil constituents under transverse compression. The broadening of the Nb3Sn diffraction peaks above critical stress values indicates reversible and irreversible Nb3Sn loading stress effects.
Highlights
The mechanical stress exerted on the coils of superconducting magnets affects their ultimate performance limits
The neutron diffraction data suggests that the magnet coil wound of Rutherford type cables can be considered as a fibre reinforced composite material
In the axial load direction the load is mainly carried by the Nb3Sn filaments and the composite stiffness can be estimated by the rule of mixtures assuming iso-strain conditions in all composite constituents
Summary
The mechanical stress exerted on the coils of superconducting magnets affects their ultimate performance limits. When the externally applied load exceeds a critical value, crack formation in the Nb3Sn filaments causes an irreversible Ic degradation [4]. It is well known that transverse compressive stress can cause a strong degradation of the Nb3Sn superconducting properties [13]. The Nb3Sn strain and stress state evolution in magnet coils during application of an external load is not well known, and the stress–strain behaviour of conductor blocks has often been modelled using estimated average isotropic material properties [15]. In this article we report, for the first time, on a direct measurement of the effect of externally applied transverse and axial compressive stress on the internal strain and stress state in the different composite coil constituents
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
