Development of a PCB rotating coil system for small-aperture multipole magnets in Korea 4GSR project

A rotating coil system mounted on a printed circuit board (PCB) was developed to precisely characterize multipole magnetic fields in magnets for Korea-4GSR project, which is constructing a 4 th -generation synchrotron light source in Korea. The system integrates a PCB-based coil shaft, high-resolution rotary encoder, digital integrator, and mercury slip ring, enabling accurate and repeatable field measurements. The accuracy and precision of the system were quantified by prototype quadrupole magnets (Q1 and Q3) from the XFEL facility. In the measurement, the quadrupole component (C 2 ) deviated by < 0.5% from the theoretical value, with measurement repeatability error of only ± 2 × 10 -5 Tm. Higher-order harmonics were ∼ 0.2% of C 2 , and their standard deviations remained uniformly low across orders. Compared to the stretched-wire method, the PCB system reduced fluctuations and increased consistency. These results confirm the system’s robustness against electrical noise and mechanical disturbances.