Design and field measurement of a dipole magnet for a newly developed superconducting proton cyclotron beamline

The design, field quality optimization, multipole field analysis, and field measurement of a dipole for a newly developed superconducting proton cyclotron (SC200) beamline are presented in this paper. The maximum magnetic field of the dipole is 1.35 T; the bending radius is 1.6 m with a proton beam energy in the range of 70–200 MeV. The magnetic field was calculated with 2D and 3D simulations, and measured with a Hall mapping system. The pole shim and end chamfer were optimized to improve the field quality. Based on the simulated results, the multipole field components in the good-field region were studied to evaluate the field quality. The results showed that the field quality is better than ± 5 × 10⁻⁴ at 1.35 T with shimming and chamfering. For the transverse field homogeneity, the third-order (B3) and fifth-order (B5) components should be controlled with symmetrical shims. The second-order (B2) component was the main disturbance for the integral field homogeneity; it could be improved with an end chamfer. The magnet manufacturing and field measurement were performed in this project. The measurement results demonstrated that the magnetic design and field quality optimization of the 45° dipole magnet can achieve the desired high field quality and satisfy the physical requirements.