Design Optimization of the Nb3Sn 11 T Dipole for the High Luminosity LHC

As a part of the large hadron collider luminosity upgrade (HiLumi-LHC) program, CERN is planning to replace some of the 8.33-T 15-m-long Nb-Ti LHC main dipoles with shorter 11 T Nb3Sn magnets providing longitudinal space for additional collimators. Whereas the present design of the 11 T dipole enables the use of RRP conductor with critical current degradation after cabling at the level of 5%, new cross sections of the cable have been studied in order to further decrease the degradation of both critical current and resistivity of the copper matrix. This change is particularly beneficial for the PIT conductor. The coil layout is reoptimized to accommodate the new cable geometry, using the ROXIE code. A set of additional design changes are implemented, such as reduction of the outer yoke diameter. In this paper, we review the main parameters of the present design, describe the changes implemented in the new design, and discuss their impact on both the electromagnetic and structural properties.