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Description
This paper presents the design of the FCC-ee booster dipole magnets. The booster dipoles are low-field iron-dominated cycled H-type magnets. They consist of an 11 meter long laminated steel yoke with anodized aluminum busbars instead of coils. The magnet is designed to mitigate parasitic effects, namely the Earth’s magnetic field and yoke hysteresis, that become significant at the 6.5 mT field required for 20 GeV injection. The analytical design is validated by Finite Element Analysis. The hysteretic effect is modeled, and the cross-section of the magnet is optimized to obtain the required field quality across the full cycle from 6.5 mT to 59 mT. The predictive power of the hysteresis model is validated by the test of a similar magnet from CERN stock. Finally, experience from a short prototype magnet, built and tested, is reported. The test results confirm that the proposed magnet meets the design requirements, demonstrating the feasibility of dipoles for 20 GeV injection energy.
