Design and Optimization of a 4 Tesla 200 mm Aperture Helium-Free Nb-Ti Nested CCT Quadrupole/Dipole Superconducting Magnet

This paper presents the design and optimization of a low-weight helium-free Nb-Ti CCT superconducting magnet (MAGDEM – MAGent DEMonstrator) for the R&D phase of the ISOLDE Superconducting Recoil Separator (ISRS) at CERN (Geneva, Switzerland). The system can be expanded to other accelerator applications demanding compact lightweight superconducting magnets, such as medical hadron therapy systems. The innovative design incorporates a dipole coil within a quadrupole coil, enhancing field integrals and operational efficiency within its concise 590 mm length. This configuration effectively achieves a 36-degree maximum bend of the particle beam, with a concentrated effort on minimizing field errors on a tightly curved path to below one unit at a peak field of nearly 4 Tesla. Additionally, the magnet includes a slightly tapered design in its straight tubes, which aids in two key areas: simplifying the assembly of the tube sets and enabling the application of radial pre-stress to the assembly. Operating at approximately 100 A, The MAGDEM design is tailored to efficiently reduce heat leakage, allowing for a single cryocooler to maintain 4.5 K. The particle storage ring of the ISRS spectrometer will incorporate a set of MAGDEM units to guide and bend the trajectory of radioactive beams using a Fixed Field Alternating Gradient (FFAG) configuration. The paper emphasizes the novel design elements, such as the tightly curved field error optimization in a straight yet tapered coil set of formers.