Development of a magnetic field monitoring system for the JAERI AVF cyclotron

We have developed a probe of a nuclear magnetic resonance (NMR) magnetometer for measurement of a fluctuation of an AVF cyclotron field. The stability of the magnetic field of the JAERI AVF cyclotron, measured with the NMR probe, was within 1 × 10 −5 . A field-measurement accuracy of the order of 1 × 10 −6 was achieved using a set of field-compensation coils and optimizing the probe position to obtain enough homogeneity of the magnetic field around the probe for measuring the cyclotron field with a high gradient. To eliminate a major bottleneck in the field measurement inside the cyclotron, the probe was specially produced with the cable shielding against RF noises and proper materials applied.