Experiment Study on Magnetic Field Homogeneity of the Persistent Current Mode Helmholtz Coils Made of HTS-Coated Conductors

High-temperature superconducting (HTS) magnet made out of coated conductors (CCs) is considered as a possible alternative for conventional LTS magnet used in MRI and nuclear magnetic resonance (NMR) because of the high critical temperature and excellent performance under strong field. However, due to the difficulty of fabricating the superconducting joints of CCs, the HTS magnet made of CCs cannot yet operate in persistent current mode (PCM). In this study, a new type of PCM coils made of CCs, called double-slit coil, is developed to fabricate a pair of Helmholtz coils with an inner diameter of 50 mm. The angle deflection of the magnetic field trapped by the double-slit coil can be reduced due to its symmetric structure on thez-axis and therefore improve the field homogeneity. Both ofz-axial andy-axial components of magnetic field distribution along thez-axis is measured at 77 K by a motor-driven hall probe with an automatic data acquisition system. The result shows that the double-slit Helmholtz coils perform similarly to circular coils on thez-axial component and they-axial harmonic component can be reduced to less than 0.2% of the total trapped magnetic field. Finally, a conceptual structure of HTS shielding coils applied in MRI/NMR.