Influence of transverse stress exerted at room temperature on the superconducting properties of Nb3Sn wires

Abstract

Results on the irreversible degradation of Rutherford cables caused by transverse stress applied at room temperature have been recently published in the frame of the Future Circular Collider study for the 16 T dipole development programme. In order to investigate the degradation process of Nb3Sn composite superconductors, experiments based on wires of the same type as used in the cable have been launched. Nb3Sn wires produced by the Restacked-Rod Process were exposed to transverse stress at room temperature and the degradation of their properties was measured. Transport current measurements near the critical temperature at self-field and magnetisation measurements with a SQUID magnetometer were performed to determine changes in performance. In addition, metallographic preparations in combination with scanning electron microscopy were carried out to reveal cracks in sub-elements. In order to determine the stress distribution within the wire, especially the stress on the sub-elements, a finite element method analysis based on results from x-ray tomography was performed. The influence of transverse stress exerted at room temperature on the critical current density and intrinsic properties is analysed and compared with the microscopic observations.