R2D2, the CEA Graded Nb3Sn Research Racetrack Dipole Demonstrator Magnet

As a part of a collaborative effort with CERN on the long road to FCC-hh, CEA is developing a 1.4 m-long single aperture short dipole demonstrator. This Nb3Sn block dipole, named F2D2, is foreseen to produce 15.5 T with a 14 % margin at 1.9 K, and will use a shell-based support structure. In order to be compact, this magnet relies on the use of different cable grades in each coil. Among the milestones in this project, a single-layer graded racetrack dipole will be constructed in order to demon-strate grading in a simplified geometry while preserving key features of F2D2. This magnet, named Research Racetrack Di-pole Demonstrator (R2D2), will permit the mastering of the fab-rication methods foreseen for F2D2 and to confirm the behavior of Nb3Sn cables representative of FCC. It should also validate some key technological aspects: compactness, operation at high-current (up to 16 kA), intermediate magnetic field (in the range of 11-12 T), and quench protection at very high energy / unit length (up to 650 kJ/m, corresponding to 168 MJ/m3).