Superconducting shim system with high purity magnetic field for NMR and MRI solenoid magnet MIDI-200

The superconducting shim system with a high purity magnetic field for the NMR and MRI solenoid magnet MIDI-200 (B/sub max/=5 T, room temperature bore 200 mm) has been designed and constructed. The system is formed by 9 fundamental shims and is positioned on a cylindrical duralumin former. The method of designing shims makes use of recursion expressions for coefficients of particular spherical harmonics in which the field of a specific current bearing conductor can be expanded. In conclusion, the theoretical configurations of correcting fields and those measured on a cylinder or spherical area are compared by the magnetic field analysis.