Efficient compensation of low-frequency magnetic field disturbances in NMR with fluxgate sensors

A simple stabilization scheme of B0 magnetic field fluctuations is described. The method is based on external measurements of time dependent magnetic field fluctuations by fluxgate sensors and generation of a compensating correction current in a coil mounted directly on an NMR magnet. It is shown that such an approach efficiently eliminates relatively slow magnetic field variations with frequency up to approximately 100 Hz. In combination with a standard 2H field-frequency lock system, the method enables acquisition of reproducible lineshapes and dramatically improves overall performance of a high resolution NMR spectrometer. The presented solution might substitute for the internal lock system in these case where deuterium lock is not available.