Measurement of magnetic field of the lattice bending magnet is important to control the beam orbit, tune control and the timing of the fixed magnetic field. Hole probe and search coil are used conventionally and NMR has been considered to know the only DC magnetic field. Authors have developed the technique for the magnetic field monitor of the pulsed magnet such as the main ring magnet of the 12 GeV KEK-PS. During the injection (550 ms) and flat top (1-2 s) periods, magnetic field is measured by NMR probes with the frequency scanning. If we want the timing pulse at any magnetic field during acceleration, NMR probe can measure it with a fixed frequency mode. It depends on the principle of the NMR, which occur the nuclear magnetic resonance in the relation between the quantum axis magnetic field and the frequency of the rotational magnetic field in the perpendicular plane. The performance of the technique for the magnetic field monitor by NMR and some unique results of the magnetic field in the lattice bending magnet are presented.
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