Study on the Process of Monolith NbTi Wire With High N-Value and High Dimensional Accuracy for NMR

NMR equipment mainly studies substances' molecular structure and physical properties. It also puts higher requirements on the magnetic field homogeneity of the equipment, which is required to reach the PPB level. Therefore, stricter requirements for processing control have also been put forward for superconducting wires. Generally, the n-value of the wires used in NMR must be over 50 at 5 T, while conventional monolith wire can only achieve 35∼45 at 5 T. In this paper, we discussed the relationship between the deformation of the filaments and the n-value. By optimizing the raw material and extrusion ratio of superconducting ingot, the deformation of the filaments is more uniform, and the n-value is increased to about 60. For conventional monolith wire, the dimensional accuracy can only achieve ± 5 µm, which cannot meet the requirement of ± 3 µm for NMR. We adopted the process of overdrawing after enameling. By changing the type of insulating material and adjusting the processing technology of overdrawing, the dimensional tolerances of the insulated wire can achieve ± 2 µm. The superconducting wire mentioned in this article can not only meet the requirement of NMR but also have application opportunities in MRI and other fields.