Novel composite reinforcement technique for HTS joints

Commercial high-temperature superconducting (HTS) tapes are limited in length, while large-scale applications such as high-field magnets require several kilometers of conductor. Joints between tapes are therefore unavoidable, and their electrical and mechanical reliability is a critical bottleneck. Soldered joints are attractive due to their relatively low resistance, but their mechanical strength is limited because of low adhesion between layers in the HTS tapes. In this work, a new mechanical reinforcement strategy was proposed and demonstrated. Anchor holes in joints allow the new composite structures, introducing different reinforcement components inside the joint, while the effect of the holes is negligible on joint resistance and critical current (Ic). Carbon fiber and epoxy fillings were used as reinforcement materials. This approach enhanced the shear strength of the joint from ∼1.2 MPa to ∼2.4 MPa, while the electrical resistivity did not increase significantly and had a very low level of ∼30 nΩ.cm2. The results demonstrated that the novel FIRM (Filling-Induced Reinforcement Matrix) approach for HTS joint can significantly improve the mechanical properties for use in high-field coils and magnets.