Room temperature shims

From NMR Wiki

Room temperature shims are coils that generate corrections to the magnetic field in the sample volume, making the field inside that volume as uniform as possible. Those corrections are generated in the form of the field gradients of different geometries. For example Z1 shim coil generates linear gradient of magnetic field along Z1 dimension (main axis of the magnet).

Adjusting currents passing through the RT shims is known as shimming and is performed each time when sample is replaced or temperature is significantly changed.

Room temperature shim coils are located in the shim stack inside room temperature bore of the magnet. Center of the shim stack should be exactly aligned with the center of probe coils (or more precisely probe is inserted to such depth so that it's coils center in the middle of she shim stack).

Shim stack, in turn is placed in the location of maximum magnetic field inside the magnet.

There also may be superconducting shim coils that are regulated only once when the magnet is installed and energized.