F2D2: A block-coil short-model dipole toward FCC

In the framework of the Future Circular Collider (FCC) program, and in collaboration with CERN, CEA is developing a 1.5-m-long single aperture Nb$_3$Sn block dipole. The so-called FCC Flared-end Dipole Demonstrator (F2D2) will produce at least 15 T with 14% margin at 1.9 K and will be assembled in a shell-based support structure. Its magnetic design is derived from the block-coil option proposed in the EuroCirCol studies and relying on graded cables for improved efficiency. The design uses identical strand dimensions but a lower critical current density according to the performance of a currently available conductor. The main challenge of this magnet lies in the concepts of joints between the conductor grades, which will be implemented for the first time in a Nb$_3$Sn block dipole. After presenting the overall design of the magnet from a magnetic and mechanical standpoint, chosen fabrication techniques are detailed.