This paper presents design and implementation of ferromagnetic shims for a conduction-cooled 3-T 100 mm winding diameter no-insulation (NI) all-REBCO magnet. The initial magnetic field profile was measured by an in-house 3-D field mapper with an NMR magnetometer, from which harmonic coefficients up to 3 order are derived. A ferromagnetic shim design code was developed, which includes an optimization process to minimize target harmonic field errors with a given volume of ferromagnetic shims. For experiment, two designed sets of ferromagnetic shim matrices, which consist of 0.025-25 mm thick iron pieces, were attached on two concentric cylindrical tubes of 54 mm and 60 mm in diameter, respectively, and then installed in a 64 mm room temperature bore of the 3 T magnet. Through recursive mapping and shimming steps, the magnet field uniformity was gradually improved from ~500 ppm to ~100 ppm. The results imply the first shimming test of all-REBCO no-insulation magnet, which will be a basis for our upcoming high-resolution all-REBCO NMR magnet currently being developed.
This work was supported by KBSI grant (D37611) to S.-G.L funded by the Korea Basic Science Institute (KBSI).