AUTHOR=Yu Cheng , Zhu Ya , Zhang Wei , Yang Jie , He Yongzhou , Zhen Tingting , Liu Tao , Lei Yangyang , Yuan Qibing , Yuan Dao , Wen Yongmei , Deng Rongbing , Jiang Zhiqiang , Deng Haixiao , Liu Bo , Wang Dong TITLE=Development of an APPLE III undulator prototype with three-dimensional force compensation for SHINE JOURNAL=Frontiers in Physics VOLUME=11 YEAR=2023 URL=https://www.frontiersin.org/journals/physics/articles/10.3389/fphy.2023.1174620 DOI=10.3389/fphy.2023.1174620 ISSN=2296-424X ABSTRACT=

The Shanghai high-repetition-rate XFEL and extreme light facility (SHINE) plans to install several elliptically polarizing undulators (EPUs) as afterburners behind the planar undulator section to obtain nearly saturated circularly polarized free-electron laser (FEL) radiation. Therefore, the SHINE R&D project needs to develop a 4-m-long EPU with an effective magnetic field of 1.5 T, a period of 68 mm, and a minimum gap of 3 mm. A magnetic force compensation EPU prototype has recently been built and tested at the Shanghai Synchrotron Radiation Facility (SSRF) based on the addition of permanent magnets. This prototype can realize magnetic compensation under various polarization modes in all working gaps, thereby reducing the deformation of the girders and maintaining sufficient rigidity of the mechanical structure. A girder deformation monitoring system was established to obtain real force compensation feedback. The final magnetic field measurement results meet the physical requirements, and the proposed scheme can be used as an alternative to the EPU with a high magnetic field and large magnetic force.