Mechanical design of a cryogenic Delta–Knot undulator for high energy photon source

A novel type of pure permanent cryogenic Delta–Knot Undulator was developed at IHEP to supply a high flux of full adjustable polarization synchrotron radiation with low on-axis power density. This prototype was an active attempt and early exploration for future APPLE–Knot undulator, which will be used at high energy photon source (HEPS). There are several challenges to develop a cryogenic delta undulator, such as the complicated structure, the influence of large magnetic force, and the magnetic measurement difficulty due to the very small gap. In this paper, the mechanical design for overcoming these difficulties will be presented in detail. A special hall measuring system is developed, and the preliminary results agree with the theoretical results. This undulator prototype will provide valuable experience for angle magnetization technology, intricate magnetic attraction structure design, and magnetic field measurement under closed small space.