Design of the longitudinal-gradient dipole magnets for HEPS
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Design of the longitudinal-gradient dipole magnets for HEPS Qing Li1 · Fusan Chen1,2 · Chunhua Li1,2 · Minxian Li1 Received: 13 October 2020 / Revised: 3 November 2020 / Accepted: 6 November 2020 © Institute of High Energy Physics, Chinese Academy of Sciences 2020
Abstract The High Energy Photon Source (HEPS) is the fourth generation light source with high brilliance and low emittance. The lattice of the storage ring consists of five different dipoles with longitudinal gradients. The longitudinal-gradient dipoles (BLGs) are permanent magnets. This paper presents the construction of BLGs and the magnetic field results using OPERA3D. By optimizing the shape of the polar surface, the magnetic field uniformity is optimized to about 2 × 10−4 . With some adjustable screws, the magnetic field is controlled accurately. Some temperature compensation shunt sheets are arranged to make the temperature stability of magnets better than ± 50 ppm/ °C. At last, the mechanical tolerances of the magnets are studied. Keywords Longitudinal-gradient dipoles · Permanent magnets design · Adjustable magnets · Temperature compensation‚ mechanical tolerances
Introduction The High Energy Photon Source (HEPS) is a 6-GeV, kilometer-scale, ultralow-emittance storage ring light source [1]. The ring consists of 48 identical hybrid seven-bend achromats (7BAs). With this lattice, the electron beam horizontal emittance of HEPS is 60 pm·rad [2]. Figure 1 shows the arrangement of longitudinal-gradient dipoles (BLGs) in one period. BLG magnets are used to reduce the emittance of the storage ring beam. There are five BLGs with the same gap 26 mm. Each of them is divided into five segments (called modules). The BLG1 and BLG5 have the same magnetic field, and the distribution of field is symmetrical about the center of period. It is similar to BLG2 and BLG4. BLG3 has a higher magnetic field than others, and the magnetic field of the central module is 1T. It is the most difficult magnet in design. In one magnet, five modules are combined together. This kind of combined magnet will have a large volume and weight if it is designed with electromagnet. It is hard to design the electromagnet for a compact magnet layout.
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Qing 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
Permanent magnets may offer a viable alternative to electromagnetic counterparts, especially where strong gradients and low power consumption are needed [3]. At present, permanent magnets have been used in many accelerators in the world, such as Fermi Lab, ESRF, APS of USA, Brazilian light source, etc. In China, two prototypes of longitudinal-gradient dipole magnet—permanent and electric magnets—were developed in HEPS-TF (2017-2019), and some experience had been got. For the HEPS storage ring, all BLGs are permanent magnets. The following key points should be considered in permanent BLGs desi
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