Final Focus Superconducting Magnets for CEPC

Final focus high gradient quadrupole magnets QD0 and QF1 are key devices of the Proposed Circular Electron Positron Collider (CEPC). They are both double aperture superconducting quadrupoles with held gradients of 136 T/m and 110 T/m, respectively. The angles between the two aperture centerlines are both 33 mrad. Though the two apertures of QD0 is in close proximity, the problem of multipole helds caused by held crosstalk is successfully solved by using cos2θ quadrupole coil with iron core. The quadrupol magnets are operated inside the magnetic held of the Detector solenoid magnet, so superconducting anti-solenoid is required to generate solenoid held that can cancel the Detector solenoid held. The hrst step of the R&D is to develop a QD0 short model magnet with a magnetic length of 0.5 m. In this paper, the layout and magnetic design of CEPC hnal focus superconducting magnets are described, and the detailed design of the QD0 short model magnet is presented.