Conceptual Design of CEPC Interaction Region Superconducting Magnets Yingshun Zhu Accelerator Center, Magnet Group Institute of High Energy Physics, Chinese Academy of Sciences 2016.4.9 CEPC-SPPC Symposium

Contents Conceptual design of superconducting magnets in single ring Design progress of QD0 in partial double ring Summary

Conceptual design of superconducting magnets in single ring Two types high gradient quadrupole magnets are needed in CEPC Interaction Region： There are two types of quadrupole magnets in the CEPC Interaction Region. The magnetic field at the pole region exceeds 7T, and these two magnets are inside the detector solenoid field of about 3.5T. These quadrupole magnets are iron-free magnets, and Nb3Sn technology must be used. The quadrupole coils have the same cross section, but with different lengths. The coils are made of Rutherford Type Nb3Sn Cables, and are clamped by stainless steel collar. The magnetic field calculation is performed by OPERA. After optimization, detailed coil cross section is obtained.

2D flux lines Magnetic flux density distribution Magnetic flux density distribution 3D model Field distribution

Main design parameters of CEPC interaction region quadrupole magnets

Anti-solenoid coil To minimize the effect of the longitudinal detector solenoid field on the accelerator beam, anti-solenoid coils are introduced just outside the quadrupoles. The total integral longitudinal field generated by the detector solenoid and anti-solenoid coils is nearly zero. Coils of anti-solenoid are made of NbTi-Cu Conductor. Magnetic field calculation is performed using axi-symmetric model, and main design parameters are obtained. 2D flux lines of Anti-QD Longitudinal field distribution of Anti-QD

Cross section of quadrupole coil and anti-solenoid coil

Design Progress of QD0 in partial double ring Compact high gradient QD0 quadrupole magnets are needed in interaction region of the CEPC partial double ring.

The field gradient of QD0 is as high as 200T/m. The minimum distance between two QD0 magnets centerline is only 45mm.The coil inner radius is 12.5mm, tight radial space is available. Serpentine winding coil using direct winding technology is selected for its high efficiency and high compactness. (experience at BEPCII) Serpentine coil is first developed at BNL, and has been used in BEPCII, J-PARC, ATF2, ILC baseline design, etc. Coil winding at BNL

Coil turns per pole is 110, excitation current is 340A. The QD0 magnet is iron-free, and its coils are made of 0.5mm round NbTi-Cu conductor using direct winding technology. Eight Serpentine coil layers are used for the QD0 coils. Collar is not needed. Coil turns per pole is 110, excitation current is 340A. 2D magnetic field calculation is performed. After optimization, the field quality for standalone QD0 is very good. Magnetic flux density distribution 2D flux lines

2D field harmonics（unit, 1×10-4） Coil layout

The field of one QD0 magnet is affected by another QD0 magnet The field of one QD0 magnet is affected by another QD0 magnet. Field cross talk of the two QD0 magnets is studied.

Since the small distance between the two QD0 magnets, the field cross talk is serious. Each multipole field inside one QD0 bore is affected by the cross talk, and the largest one is a dipole field. One layer of shield coil is introduced just outside the quadrupole coil to improve the field quality, and the effect is obvious.

Summary It is challenging to develop high gradient superconducting magnets in CEPC Interaction Region. Conceptual design of superconducting magnets in single ring is performed. Serpentine coil using direct winding technology is suitable for QD0 in partial double ring. Cross talk effect should be further compensated in 3D field calculation.

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