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Description
Synchrotron radiation facilities impose stringent requirements on the magnetic field quality, stability, and lifetime of undulators. During long-term operation of a beamline at the Shanghai Synchrotron Radiation Facility (SSRF), a gradual degradation of photon-beam performance was observed. To identify the cause, the cryogenic permanent magnet undulator of this beamline was warmed up and re-measured at room temperature during the summer shutdown. The on-axis field was found to be most strongly attenuated in the upstream region, with a maximum reduction of about 20% that gradually relaxed towards the downstream end. In addition, several sharp local drops of the magnetic field were detected in the central section. Visual inspection revealed pronounced melting holes in the copper foil in this area, indicating localized electron-beam impacts that likely damaged the underlying magnets and led to the abnormal field reduction. This paper presents the magnetic measurement results and the longitudinal attenuation pattern of the radiation-damaged undulator, and describes how local magnet replacement, re-shimming, and re-measurement were used to refurbish the device, providing a reference for future operation, maintenance, and radiation-protection design of similar undulators.
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