Design of superconducting quadrupole magnets in CEPC interaction region

High-gradient quadrupole magnets are required in the interaction region of the proposed Circular Electron Positron Collider (CEPC) to achieve high luminosity. On each side of the interaction point, there are three sets of dual-aperture superconducting quadrupole magnets, namely Q1a, Q1b, and Q2. The angle between the two aperture centerlines is 33 mrad, and the required field gradient of the first quadrupole Q1a is as high as 142.3 T/m. The local dipole field in each quadrupole aperture is required to be smaller than 300 Gs. In view of the updated design requirements, an iron-free Canted Cosine Theta (CCT) quadrupole coil design is selected. Two CCT technical routes are studied: the coil in groove of the skeleton scheme and the direct winding CCT coil scheme. Coil structure adjustment is employed to mitigate the magnetic field crosstalk between the two apertures. In this paper, the magnet design, field simulation, crosstalk compensation, and design parameters of the three CCT quadrupole magnets are presented, and the two technical routes are compared and discussed.