The magnetic field measurement and optimization method of a small gap superconducting undulator

Abstract: [Background]: A superconducting undulator prototype with the length of 4 m, the period length of 16 mm, and the gap of 5 mm for the Shanghai High Repetition Rate XFEL (X-ray free electron laser) and Extreme Light Facility (SHINE) has been successfully integrated and tested. [Purpose]: This paper proposes a magnetic field point measurement method based on dual Hall probes specifically for the small gap superconducting undulator. [Methods]: The measurement principles are described, and magnetic field measurements and optimization experiments are conducted on the prototype. The magnetic field optimization is achieved by segmentally adjusting the excitation current of the middle 2 m section of the superconducting undulator. [Results]: As a result, the phase error in this section is reduced to less than 5 ° at an excitation current of 100 A, meeting the design requirements. [Conclusions]: The experimental results confirm the effectiveness of the proposed magnetic field measurement and optimization method.