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

本文研究了用加强带绕制的Bi 2212包银带线圈在Hoop或压应力状态下的超导性能。此外，针对低温冷却超导磁体的应用，还研究了测试线圈的热稳定特性。本文重点研究了高温超导体的磁通流动状态，并探讨了这种稳定的磁通流动电阻率作为一种新的磁体技术的可能性。作为克服高温超导体大环向应力的一种新的尝试，通过对Hastelloy合金带材进行拉伸缠绕，增加了Bi 2212带材的残余压应变。这导致了用Hastelloy合金带材增强的Ag护套Bi 2212带材承受270 MPa的大应力。此外，在横向压缩应变状态下的临界电流特性进行了测量的Ag护套Bi 2212测试线圈与哈氏合金加强带。在超导材料高场实验室的无致冷剂超导磁体中安装了一套测量临界电流下横向压应变效应的装置。取决于增强方法的传输电流特性进行了比较彼此，variing施加的磁场高达10 T。有人发现，在10 MPa的横向压应力下发生的Ag-护套Bi 2212磁带线圈没有增强的40%的IC退化，和相同的退化对应于在40 MPa的增强Bi 2212磁带线圈。对Bi 2212银包层带材的热稳定性进行了实验研究，结果表明：Bi 2212带材在低温冷却条件下的热稳定性与冷却功率密切相关，通过保持冷却平衡，可以使带材在Ic以上的发热状态得到足够的稳定。

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.