Investigation of Magnetic Properties in Precisely Machined RE-Ba-Cu-O Bulk Superconductors for Use in Undulator Systems

A 50-period high-temperature superconducting (HTS) undulator consisting of staggered-array Gd-Ba-Cu-O (GdBCO)/Ag bulks is under development for application at the Shanghai Soft X-ray Free Electron Laser facility. The key fabrication challenges include precision electrical discharge machining of over 100 cylindrical bulks into half-moon shapes, shrink-fitting into copper sleeves, and grinding each assembly to 4 mm thickness, all while preserving superconducting properties. This paper presents the fabrication process and magnetic field mapping results of all completed samples, which were field-cooled and magnetized using a 0.3 T electromagnet at 77 K. Cracked samples were identified and excluded based on their trapped field profiles. The remaining qualified samples were assessed by integrating the trapped magnetic field over a specified area to quantify their superconducting performance, then sorted and positioned in a staggered-array undulator configuration. Simulation results indicate that the magnetic field inhomogeneity can be reduced to 1.9%, a level suitable for further optimization through adjustment of the ferromagnetic pole heights.