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Description
In the framework of the CERN-CEA collaboration and as part of the HFM program, CEA is developing the R2D2 magnet. This magnet is a key milestone in the development of Nb3Sn high field block coil magnets with grading for future circular colliders. R2D2 is a 1.6-m long dipole made of two Nb3Sn racetrack coils, each one made of two different conductors wounded together in order to explore the grading concept. The R2D2 magnet support structure is based on three shell segments and bladders-and-keys technology for the transverse preload, as well as four tie rods and end-plates for the longitudinal preload. The shell segments, the rods, and the coils are instrumented with strain gages to monitor the mechanical loading. To validate the structure and characterize its behavior, an instrumented aluminum dummy coil was used to replace the Nb3Sn coils inside the coil pack. This assembly was first loaded transversely and then axially, before being cooled-down at 77 K in liquid nitrogen. This paper summarizes the various steps of R2D2 support structure practice preload and cooldown, with a major focus on the analysis of the structure mechanical behavior extracted from strain gages measurement along with the correlation with FEM models.
