Suppression of the critical current degradation under the compressive stress on the internal reinforcement bronze processed Nb3Sn wire using Cu-Sn-In ternary bronze alloy matrix

Abstract

Typical large current capacity conductors for fusion magnet are often manufactured by the Cable-In-Conduit (CIC) method. The CIC conductor is fabricated by twisting multiple Nb3Sn strands and pure Cu wires, and huge local stress/strain concentration alike the point contact was observed in each twisted Nb3Sn strand applied to transverse compressive load based on the electromagnetic force. These concentrations caused to the Nb3Sn filament breakage and it was also a major factor of the current sharing temperature (Tcs) and critical current density (Jc) degradation on CIC conductor. Mechanical strength improvement of the Nb3Sn strand is required to realize superconducting magnet under higher electromagnetic force for a future DEMO. Recently, we succeeded to fabricate the internal matrix reinforcement bronze processed Nb3Sn multifilamentary wire using a Cu-Sn system ternary alloy matrix containing Indium (In) element.In this study, critical current (Ic) property with the in-situ compressive stress on the internal matrix reinforcement Nb3Sn wire was evaluated. The compressive stress obtained to the Ic deterioration of 5% on the internal matrix reinforcement Nb3Sn wire was confirmed at 150 MPa, and this stress was 3 times higher than Nb3Sn wire without reinforcement. We found that the internal matrix reinforcement was one of the great advantage methods to suppress the Ic degradation by the compressive stress.