Design Optimization of the New D1 Dipole for HL-LHC Upgrade

The High-Luminosity Large Hadron Collider upgrade (LHC) project aims to increase the peak luminosity of the LHC to 5 ×10³⁴ cm ^{- 2}s ^{- 1}, and a total integrated luminosity of 3000 fb ^{- 1} from 2020 to 2030 by upgrading the low-beta insertion system for the ATLAS and CMS experiments. The aperture of the insertion magnets including the focusing/defocusing quadrupoles and separation dipoles will be doubled to achieve a smaller β*. This paper presents the latest design updates of the separation dipole D1 magnet, including the study of the different cable types to vary the main field; the modifications of the iron shape for the new design options to minimize the iron saturation effect on field quality; and the optimization of the coil ends to reduce the peak field and higher order harmonic field integrals in the ends.