Design and Prototype Development of a Combined-Function Quadrupole-Sextupole Magnet for the SPS-II Booster Synchrotron

The development of a prototype booster magnet for the Siam Photon Source II (SPS-II) was launched in 2023 as a milestone in advancing accelerator technology through domestic manufacturing capabilities in Thailand. In the SPS-II booster lattice, the magnet integrates focusing quadrupole and sextupole functions into a combined-function quadrupole-sextupole magnet, enabling a more compact lattice and reducing the total number of magnets required. To meet the required magnet specifications, the design was carefully optimized using Opera-3D software (version 2021) to achieve a quadrupole gradient of 19.395 T/m and a sextupole gradient of 22.327 T/m2 over an effective magnetic length of 0.25 m, while maintaining a magnetic field homogeneity better than 1 × 10−3. A key manufacturing challenge involved fabricating laminated magnet cores and establishing precise production processes. Magnetic field measurements performed on the prototype using the Hall-probe technique validated the magnet’s quality and accuracy. This paper presents the overall development process, including the magnet design, details of the magnetic field simulation methodology, prototype fabrication, and initial magnetic field measurements.