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

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 (T_cs) and critical current density (J_c) 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 (I_c) property with the in-situ compressive stress on the internal matrix reinforcement Nb₃Sn wire was evaluated. The compressive stress obtained to the I_c 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 I_c degradation by the compressive stress.