Precise pulsed magnetic field mapping using a compact pick-up probe for a pulsed sextupole magnet

A pulsed sextupole magnet was used for beam injection at the KEK-Photon Factory (KEK-PF). During the top-up injection, oscillation of the stored beam was observed. To investigate this issue, a compact pick-up probe has been developed for measuring peak fields around the zero-magnetic-field region where the stored beam passes. The probe has two coils: a main coil and a background coil. The width and length of the main coil are only 3.2 and 5.8 mm, respectively. The voltage signal from the background coil is subtracted from that of the main coil to obtain an effective voltage signal. The results show that the peak field of a pulsed magnet can be measured with a sufficient accuracy for magnetic field mapping. A magnetic field signal with an amplitude of 2.2 × 10^-4 T was measured clearly. The longitudinal field structure that contains the magnetic field generated by the eddy-current effect was observed, which explains the oscillation of the stored beam at the KEK-PF.