Mechanical Design of FalconD, a Nb$_3$Sn Cos$\theta$ Short Model Dipole for the FCC

The future of the particle accelerators points to a new CERN’s circular collider with an order of magnitude increase in the center-of-mass energy compared to the Large Hadron Collider (LHC). To achieve this increase from 14 TeV to 100 TeV a 100 km tunnel will be required to host the collider. This particle accelerator requires a new generation of double aperture superconducting magnets, capable of generating a high quality, stable 16 T magnetic field in a 50 mm bore. To manage this challenging task a roadmap was planned in the development of accelerator-grade Nb $_3$ Sn magnets under a specific four-year CERN-INFN (Italian Institute for Nuclear Physics) agreement. The first step will be the construction of a short, single aperture cos $\theta$ dipole, with a target magnetic field of 12 T and an ultimate field of 14 T. In this contribution, the mechanical design of this short model, called Falcon Dipole (Future Accelerator post-LHC Cos $\theta$ Optimised Nb $_3$ Sn Dipole) will be presented. To generate the required field, this magnet will feature a two-layer design, with state-of-the-art Nb $_3$ Sn conductor. This work is focused on the mechanical analysis of this short model. To cope with the intense magnetic forces that are generated in the magnet during operation and to ensure the integrity of the conductor, a novel mechanical structure has been identified, the so-called “bladder & key” (B&K), a technique that has never been used in cos $\theta$ dipoles and needs to be validated. In conclusion, this paper presents 2D and 3D FEA able to describe the constructive steps that meet the requirements imposed by the project to ensure the correct operation of this magnet.