Evaluation of the Screening Current in a 1.3 GHz NMR Magnet Using ReBCO

NMR magnets using high-T_c superconductors (HTS) are currently by several organizations designed to generate high fields exceeding 25 T. In such designs, the HTS are used for the inner coils, and the outer coils consist of NbTi and Nb₃Sn wires. A ReBCO wire with a Hastelloy substrate has excellent critical current performance over wide range of magnetic fields and tolerates high tensile stress up to 700 MPa. We have previously shown conceptual designs in which the main coils are assumed to use ReBCO wires. The designs suggest the potential to realize much more compact and lightweight magnets than conventional magnets with low-T_c superconductors (LTS) and HTS. On the other hand, the problem of screening current induced by the perpendicular field remains to be solved. In this study, we evaluate numerically the amount of the magnetic field generated by the screening current in ReBCO coils. Compensation coils for improving field homogeneity were found to reduce the shielding current by several percentage points. The improved coil arrangement is reported considering the shielding current effect.