Mechanical Optimization and Study of the Superconducting Magnet CHiC

Hadron therapy is a medical treatment that employs hadronic particles (e.g. carbons ions, protons) to treat tumours. Carbon ions are very effective among the different hadrons employed due to their high and localized energy deposition. Their use is, however, limited because of the high cost and size of facilities required to handle these particles. Some treatment facilities being studied include a gantry, a rotating machine that delivers the particle beam from different directions, thus drastically improving the treatment effectiveness. A new European ion gantry for carbon ions is being designed to reduce its weight and cost, making hadron therapy more widely accessible. In gantries, magnets bend and guide the particles through their path towards the patient. One of the magnet demonstrators for this application is CHiC (Closed Helium Circuit Cooling), which is under study at CERN and consists of a Cosθ coil sustained by a mandrel (called former) instead of traditional collars. The paper shows the study of CHiC mechanical structure and presents, for the first time in magnet design, the full description of an analytical model developed to identify the key parameters affecting the system performance, aiming at extending the initial and limited range of manufacturing tolerances to make the design compatible with standard fabrication techniques. The paper justifies all steps of the model development and its validation by Finite Element Models (FEM). Then, it describes how to use the analytical model to improve the system behaviour significantly. The analytical model successfully predicts the system behaviour and optimizes the magnet initial design, extending the range of mechanical tolerances for key components by ∼170%. The analytical model developed allows for a robust understanding of the system behaviour and how to modify the design to achieve the objectives effectively. Finally, the model is of general use and can also be applied to other magnets to improve their design successfully.