Evaluation for characteristics of Bi-system high temperature superconducting wires under large electro-magnetic stress

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Superconducting properties under the large electro-magnetic stress state of Hoop or compressive stress were examined for a Ag-sheathed Bi2212 tape coil cowound with reinforcing tape. Further, the thermal stability characteristics for the test coil were also studied, aming to an application for a cryocooled superconducting magnet. Especially, we focused on the flux flow state of high temperature superconductors, and investigated the possibility whether such a stable flux flow resistivity without quenching could be applied as a new magnet technology or not.As a new attempt to overcome the large Hoop stress, the residual compressive strain for Bi2212 tape was added by tension-winding of Hastelloy alloy tape. This results in standing with the large stress of 270 MPa for Ag-sheathed Bi 2212 tape reinforeced with Hastelloy alloy tape. Moreover, the critical current characteristics in a transverse compressive strain state were measured for the Ag-sheathed Bi2212 test coil with Hastelloy reinforcing tape. An apparatus for measuring the transverse compressive strain effect in the critical current was installed into a cryogenfree superconducting magnet at the High Field Laboratory for Superconducting Materials. The transport current properties depending upon the reinforcement method were compared with each other, varing the applied magnetic fields up to 10 T.It was found that the Ic degradation of 40 % was occurred at the transverse compressive stress of 10 MPa for the Ag-sheathed Bi2212 tape coil without reinforcement, and that the same degradation corresponded to the reinforcing Bi2212 tape coil at 40 MPa. From the experimental results on the thermal stability for the Ag-sheathed Bi2212 tape, we can understand that the thermal stability in the cryocooling condition is closely related with the cryocooling power, and that the heating state above Ic is stabilized enough by keeping the cooling balance.