Mechanical Design of the 4 T Curved Demonstrator Dipole for the SIG Gantry

A new generation of superconducting magnets for applications in ion therapy is under study in the frame of a collaboration between CERN, Centro Nazionale di Adroterapia Oncologica (CNAO), Istituto Nazionale di Fisica Nucleare (INFN) and MedAustron. One of the most critical aspects of these new ion therapy facilities is the optimization of rotatable gantry to treat the patient from all the directions. Within this context, the INFN is taking part in the effort through the development of the Superconducting Ion Gantry (SIG) project. This program aims to design, manufacture and test a superconducting Nb-Ti, single aperture, cos-theta dipole, 80 mm in aperture, with a remarkable radius of curvature of 1.65 m. This magnet is critical for the design of a cutting-edge, weight optimized, 430 MeV/u carbon ion gantry. The project has the objective of proving the feasibility of such challenging magnets by winding and assembling a short demonstrator of 30$^\circ$ angular sector and about 1.3 m in length, followed, possibly, by a full-length 45$^\circ$ model. The magnet will be assembled and tested at the INFN Laboratorio Acceleratori e Superconduttività Applicata (LASA). In this contribution a preliminary 2D design of the mechanical structure is presented. The magnet features aluminum collars around the coils to convey the azimuthal preload, and a system of aluminum clamps to both hold the two halves of the iron yoke together, but also to convey the longitudinal preload, avoiding the usage of tie-rods.