An online magnetic field measurement system to detect radiation damage in undulators

Abstract To detect potential magnetic demagnetization or depolarization in insertion devices such as undulators and wigglers, which operate in high-radiation environments, this study proposes a novel magnetic field measurement method. This method is based on Faraday’s law of electromagnetic induction and the structural characteristics of variable-gap undulators. Specifically, Flexible Printed Circuit (FPC) boards are placed at the center of the undulator gap. By adjusting the gap, the system measures the induced voltage of each coil during the gap’s opening and closing process. Experimental results confirm that this method maintains consistent integral voltage during each half-cycle of the gap adjustment. Furthermore, when comparing the integral voltage data obtained using this method with the first integral data from a traditional Hall probe measurement, both trends exhibit a high degree of consistency. Further analysis shows that the electron trajectory deviation (FS) results calculated from both methods also align closely. These findings demonstrate that the proposed method enables reliable long-term, real-time monitoring of the magnetic field state of undulators in operation, showcasing its feasibility and practical application potential.