Multipole analysis for absolute magnetic field measured by multiprobe pulsednmr method

Vor accelerator dipnlc magnets, the study on muttipole coefficients in n Int:) region is useful for understanding magnet characteristics and checking a construction procedure. The multipro be pulsedNMR method is ücandidate for measurement of the local multipulc coefficients. For the absolute fields measured by the multiprobe pulsedNMR method, a rigorous application of the Fourier expansion is found In yield multipulc coefficients. It is made clear that the direction of the dipolc field is unable to be determined by the Fourier expansion alone. For estimating alignment accuracy of pulsedNMR probes, the relationship between errors of multipolc coefficients and those of probe positinn is derived by the Fourier expansion method. For applying of multiprobe pulsedNMR method to accelerator dipole magnets, we designed and fabricated a field measuring system using two probes. The probes had NMR colls wound around glass ampuls with a diameter of about 1.4 mm. The NMR signal was processed with a phase lock loop circuit to produce the NMR frequency. Dipole field uniformity and multipnle coefficients were measured at A.35 T for a 1.5 m long dlpolc magnet. It was confirmed that the Held data by this NMR system had an accuracy of 10s.