Abstract
A PCB-based bucking rotating coil system was developed for high-precision measurements of small-aperture quadrupole magnets in the Korea Fourth-Generation Synchrotron Radiation Source (4GSR). The sensor consists of a 14-layer PCB with 84-turn main coils and 126-turn compensation coils, providing effective suppression of the main quadrupole component. The system was evaluated using a prototype Q31 quadrupole magnet. After applying a 40 μm geometric offset correction, the difference between the rotating-coil and Hall-probe measurements was reduced from 2.5% to 0.003%, with a repeatability better than 7.0 × 10−5. The normalized sextupole and allowed harmonic components were measured as B3/B2 = 2.82 × 10−3 and B6/B2 = 4.55 × 10−4 in non-bucking mode, and were reduced to 3.52 × 10−4 and 7.46 × 10−5 in bucking mode. The measured bucking ratio agreed well with the geometrical bucking ratio of 652. The results demonstrate that the developed system provides accurate and repeatable harmonic measurements for quality control of 4GSR quadrupole magnets.