Influence of torsional strain on the Bi-2212 tapes and round wires under background field

As the only high-temperature superconductor (HTS) that can be made into round wire without anisotropy, Bi-2212 round wire holds significant potential for applications as CICC (cable in conduit conductor) for superconducting magnets in fusion reactors. However, Bi-2212 is brittle and sensitive to strain which leads to a low mechanical performance. The effort on studying the impact of strain on the transport properties is mainly focus on the axial strain. However, the conductor will be inevitably subjected to torsional strain in the CICC. The torsional strain of Bi-2212 under background magnetic field has been rarely reported. In this paper, the critical current (Ic) of Bi-2212 tape and round wire under torsion and background magnetic field is investigated and compared with each other. The measurement is performed at 77 K and 0-20 mT. The result demonstrates that the Ic of Bi-2212 tape is strongly dependent on the magnetic field angle, while magnetic field angle has little influence on round wires. Although the external magnetic field and torsional angle have impact on Bi-2212 tape and round wire, the Ic degradation of tested samples is more dependent on external magnetic field intensity than that of torsional angle.