Magnetic design of the K-4GSR combined-function booster dipole magnet

The K-4GSR project targets a 4.0 GeV 4th generation synchrotron radiation source with $$\sim $$ 800 m circumference and 4 GeV beam energy. It features a 7 Multi-Bend Achromat (MBA) lattice structure with a beam emittance of less than 100 pm. It employs a 4 GeV full-energy injection using a booster installed in the same tunnel with the storage ring. The booster ramps the 200 MeV injection beam to 4 GeV beam energy for the storage ring injection and operates at 2 Hz. The booster consists of 60 combined-function dipoles, and 66 quadrupoles, with additional sextupoles and correctors. Combined-function dipoles are chosen as bending lattice elements to minimize the number of magnets and the total costs. In this study, the 2D pole face optimization, the 3D FEM analysis, and a detailed reference orbit, which is slightly different from a pure bending orbit are analyzed.