Organic free montmorillonite-based flexible insulating sheaths for Nb3Sn superconductor magnets

Nb3Sn is a superconductor that exhibits higher performances than NbTi alloy currently used in superconducting magnets, regarding both the critical magnetic field and critical current. However, Nb3Sn is an intermetallic compound prepared by thermal treatment, which loses ductility and plasticity once reacted. Since organic materials cannot be used as insulating sheaths and applied before the thermal treatment required for the synthesis of Nb3Sn, a clay mineral-based organic-free sheath was prepared, which can be applied to Nb3Sn magnetic coils prepared by the wind & react method, before the thermal process. This process allows for facile shaping of the superconductor precursor, before reaction, along with the application of the insulating coating, the sintering of this coating being achieved by the thermal treatment required for the synthesis of Nb3Sn. This process has been designed for industrial developments and facile scale-up. The final material is an organic-free ceramic ribbon that can be stored before further use as an insulating sheath of Nb3Sn wires, and electrical and magnetic tests on both the material and a specific demonstrator made with a 20 m superconducting reel, demonstrate that this material can be used as an insulating sheath, with no side-effect on superconductor properties.