Absolute calibration of the NMR magnetometers and of the magnetic field measuring system used in the CERN muon storage ring

The nuclear magnetic resonance (NMR) magnetometers designed for the measurement of the magnetic field of the Muon Storage Ring have been described in a preceding paper (see ibid., vol.143, p.203 (1977)). Here we report results on the measuring accuracy of these units. The tests were extended over the range of local gradients which exist in the storage region from better than 1 ppm/cm to the worst case of some 300 ppm/cm. The magnetic field is 14.7 kG. All NMR probes used for the mapping and monitoring of the magnetic field have been absolutely calibrated with calibration probes especially constructed for this purpose. All corrections applied to the measured NMR frequencies in order to get the spin precession frequency of a free proton in the same magnetic field are summarised. (8 refs).