Single-block measurement for the cryogenic permanent magnet undulator sorting
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ORIGINAL PAPER
Single-block measurement for the cryogenic permanent magnet undulator sorting Ling-Ling Gong1 · Xiao-Yu Li1 · Yu-Hui Li1 · Ya-Jun Sun1 · Hui-Hua Lu1 · Ke-yun Gong1 · Qing Guo1 · Shu-Chen Sun1 · Zhi-qiang Li1,2 · Wan Chen1 Received: 28 September 2020 / Revised: 19 October 2020 / Accepted: 31 October 2020 © Institute of High Energy Physics, Chinese Academy of Sciences 2020
Abstract Purpose The magnet sorting is a standard step in the undulator fabrication procedure. The shortest undulators period used in the High Energy Photon Source (HEPS) is only 12 mm. To the short period undulator, the sorting may be more important than the long-period undulator. Normally, the Helmholtz measurement is used as the input for the work. It is the averaged orthogonal magnetization of each block. In order to investigate whether the Helmholtz coil measurement is enough for the sorting, a careful study has been made. Method Firstly, a magnetic camera was used to scan the 3D surface field of a magnet. Afterward, its field integral is measured by the stretched wire. In the measurement, the magnet was placed at different statuses. The results were checked to see whether they are consistent with expected features supposing a homogeneous magnetized block. Finally, the results measured by the Helmholtz coil and the stretched wire were compared. Results The surface field scan demonstrates that the field over a magnet block is inhomogeneous. Moreover, the field integral measurement by the stretched wire also shows big difference when the different magnet sides toward the wire. The comparison between the stretched wire and the Helmholtz coil measurement shows no correlation. Conclusion The study presented in this paper reveals that the homogeneity of the magnetization is imperfect. Therefore, the Helmholtz coil data are insufficient to the short-period undulators sorting. Keywords Magnet sorting · Undulator · Stretched wire · Helmholtz coil
Introduction The insertion devices, especially the undulators, are widely used in the accelerator-based light sources, including the facilities of free electron lasers and the synchrotron radiation. As a large-scaled light source, each facility serves tens of users from different scientific or industrial backgrounds. To satisfy various users’ requirement, the photon energy covers a large range and even extends to the ultrahard X-rays. For example, the Chinese High Energy Photon Source (HEPS) [1] takes use of 6 GeV electron beams and its maximum
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Yu-Hui Li [email protected]
1
Laboratory of Particle Acceleration Physics and Technology, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China
2
University of Chinese Academy of Sciences, Beijing 100049, China
photon energy is even higher than 100 keV. According to the on-axis resonance condition, K2 λu 1+ λr 2nγ 2 2
(1)
where λr is the radiation wavelength, λu is the undulator period, n is the harmonic number, γ denotes to the beam energy and K is the so-called undulator parameter, the shorter waveleng
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