Irreversible degradation of Nb₃Sn Rutherford cables due to transverse compressive stress at room temperature

Summary

In the framework of the Future Circular Collider design study for a 100 TeV circular collider, 16 T superconducting bending magnets based on Nb$_3$Sn technology are being developed. A pre-stress on the conductor during magnet assembly at room temperature (RT) is needed to counteract the Lorentz forces during operation. The superconducting properties of the brittle Nb$_3$Sn superconductor are strain sensitive and excessive pre-stress leads to an irreversible degradation of the superconductor. In order to determine the level of acceptable pre-stress during the magnet assembly process, reacted and impregnated Nb$_3$Sn cables were exposed to increasing transverse compressive stress up to a maximum stress level of 200 MPa at RT. After each stress cycle, the critical current of the cable specime