Design Comparison of Four-Layer Full-Nb$_{3}$Sn and Hybrid Nb$_{3}$Sn/NbTi Cos-Theta Dipoles for the CERN High Field Magnet R&D Programme

The High Field Magnet (HFM) R&D programme at CERN aims to find technological solutions for the construction of accelerator magnets to be installed in future post-LHC colliders. The Italian Institute for Nuclear Physics (INFN) and CERN are collaborating to design and fabricate a new four-layer cos-theta dipole able to achieve a bore field of 14T with at least 20% margin on the load-line. Two design options are under evaluation: a four-layer dipole entirely made of Nb3Sn, and a hybrid configuration combining inner Nb3Sn layers with outer NbTi layers. Both options are being assessed for feasibility as short models, with scalable design choices for longer magnet prototypes suitable for accelerator integration. This paper presents a comparative study of the performance of the two design options. The results provide insights into the trade-offs between performance, complexity, and protection constraints in the development of next-generation high-field dipole magnets. The Full-Nb3Sn solution satisfies the HFM requirements, but the Hybrid solution is a promising, cost-effective alternative that can be considered for next-generation colliders.