Quench Protection of Nb3Sn High Field Magnets Using Heaters, a Strategy Applied to the Graded Racetrack Dipole R2D2

The quench protection for the Future Circular Collider (FCC) 16 T Nb 3 Sn dipoles was based either on the CLIQ (Coupling Loss Induced Quench) system, or on resistive quench protection heaters. Several heater designs were sketched during the iterative magnet design processes. This led to identifying some rules about an effective heater design in the full-scale 14-m-long magnets. Following the FCC study, short dipole magnet models are being built to test the novel features that were envisioned for the FCC magnets. In this work, we review the principles of effective heater design, and then apply this methodology to the graded block dipole short model R2D2, which is being designed at CEA Saclay. This magnet has high current density in copper after quench, which makes the protection challenging and requires pushing the heater technology to its limits.