AUTHOR=Wei Junhao , Yang Xiangchen , Chen Zilin , Zhang Xiangzhen , Bian Xiaojuan , Li Yuhui TITLE=Development of NbTi planar superconducting undulators at the IHEP JOURNAL=Frontiers in Physics VOLUME=11 YEAR=2023 URL=https://www.frontiersin.org/journals/physics/articles/10.3389/fphy.2023.1153005 DOI=10.3389/fphy.2023.1153005 ISSN=2296-424X ABSTRACT=

Superconducting undulators (SCUs) have the advantages of generating stronger magnetic field and the radiation hardness compared to permanent magnet undulators. Therefore, SCUs are valuable to be applied in the free-electron lasers (FELs) driven by high-repetition-rate linear accelerators. The Insertion Device Group at the Institute of High Energy Physics (IHEP) in China started an R&D project to produce NbTi planar SCU prototypes with 15 mm period length. Several SCU prototypes, including short mock-ups, a 0.5-m-long SCU, and a 1.5-m-long SCU, have been successfully produced and cryogenic tested. The short mock-up coils were cooled by a liquid helium free cryostat to be quench trained at 4 K. The maximum current in the coils reached 500 A and the magnetic peak field exceed 1 T with 7 mm gap. The 0.5-m-long SCU was tested by using a vertical test system. The correction coils were confirmed with the ability in both correcting the magnetic field integrals and the phase error. The 1.5-m-long SCU was not only vertically tested, but also installed in a cryostat to be operated with high current over a long time. We applied the gap adjustment method to reduce the phase error within 9 degrees. The development of SCUs at the IHEP is introduced in this paper in detail.