Shimming, the iterative adjustment of the currents passed through correction coils placed around the active volume of an NMR magnet in order to maximize the homogeneity of the magnetic field, wastes thousands of hours of spectrometer and operator time each year. It is a tedious and at times a frustrating task, and few instrument operators would hesitate to delegate it to an automatic system were such a system to be efficient, general, and reliable. This Communication describes what may prove to be just such a system: information from spin-echo experiments on the solvent deuterium resonance using pulsed shim coil currents is used to calculate iterative shim current corrections, giving rapid convergence to excellent field homogeneity. Although the present experiments have been restricted to optimization of the most important set of shims, those acting along the long (z) axis of the sample, in principle the method can be extended to shim all gradients.
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