Impact of Indentation on the Critical Current of Bi2212 Round Wire

CFETR, "China Fusion Engineering Test Reactor," is a new tokamak device. Its magnet system includes the toroidal field (TF), central solenoid (CS), and poloidal field coils. The main goal of this project is to build a fusion engineering tokamak reactor with fusion power of 50-200 MW and self-sufficiency by blanket. The maximum field of CS and TF will get around 16 T, which is much higher than that of other reactors. New materials could be used to develop the technology of magnet for the next generation of fusion reactors. Bi₂Sr₂CaCu₂O_x as a potential material is considered. However, the Bi-2212 phase is brittle, and the sheath of the round wire (RW) is Ag/Ag-Mg alloy with high plasticity and low strength. During cabling or conductor manufacturing, the compression on wire is inevitable, which could cause severe indentation on wire. With the aim of investigating the impact of indentations on the critical current of Bi-2212, the artificially indented wires were made, and I_c was measured. The results show that I_c of a Bi-2212 RW, unlike Nb₃Sn and NbTi wires, linearly decreased by the increased depth of indentation. The results are foreseen to be useful for Bi-2212 conductor design and manufacturing.