Gain calibration for eliminating X-Y coupling in X-ray beam position monitors at SPring-8 photon beamlines

Although synchrotron radiation originates from charged particle beams, monitoring its positional stability requires distinct technical approaches. To enhance the accuracy of position and angle measurements of the synchrotron radiation beam at SPring-8 BL15XU, both a quadrant-type XBPM and a fixed-blade XBPM were installed on the same beamline. In the quadrant-type XBPM, widening the detector spacing led to noticeable X-Y coupling. To address this, a 2×2 correction matrix was introduced to perform linear transformation of the measured signals. The proposed method successfully eliminated X-Y coupling while maintaining resolution, enabling simultaneous operation of both XBPMs.