Magnet shim coils

Cryoshims Rough (superconducting) shim coils that are built into superconducting magnets and adjusted at installation of the instrument. 

Shim coils Coils built into NMR magnets designed to improve the homogeneity of the magnetic field experienced by the sample. Two types of shims are used cryoshims and room temperature shims. Normal shimming involves the use of the room temperature shims. 

Shimming The process of adjusting current flowing through the room temperature shim coils in order to achieve optimal magnetic field homogeneity prior to the acquisition of NMR data. The process may be performed manually or under automation. 

The magnetic field inside a superconducting solenoid is not particularly homogeneous, and compensation of the field gradients is quite a complex problem that has been solved49 by the provision of mathematically designed arrays of superconducting or normal, resistive shim-coils, or both. 

The shim coils are constructed based on an expansion of the magnetic field inhomogeneity in terms of spherical harmonics. The fields produced by the coils are orthogonal and can be adjusted independent of each other. Following (2.1.18) the shim fields Bs m are characterized by the associated Legendre polynomials P m (cos 6) and the expansion... 

The gradient coils are inserted inside the room temperature shim coils in the magnet (Fig. 2.3.1). Depending on the type of spectrometer, they can be part of the magnet assembly or part of the removable probe assembly. The former are typical for medical... 

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