Proton therapy for the treatment of cancers adopts a rotating system called gantry to irradiate the tumor from any direction. The gantry system consists of different beam line magnets that bend the proton beam towards the patient. The use of superconducting magnets allows reducing the size and weight of the last bending section. During the gantry operation, it is necessary to change the magnetic field of the last bending in order to vary the proton penetration depth. The electrodynamic transients in the superconducting strands and cables generate losses that must be computed for a proper design of the cryogenic system. Two main types of losses must be accounted for when dealing with multistrand superconducting cables, related to the magnetization and coupling of the superconducting filaments (intrastrand losses) and to the current loops induced between different strands during electrodynamic transients (interstrand losses). This work describes the methodologies and numerical codes adopted to compute the hysteresis and coupling losses in an innovative magnet system designed by PSI for future superconducting gantries. In this design the superconducting coils are wound using Nb3Sn Rutherford cables. The validation of the numerical tools versus analytical results is presented for simplified cases with uniform magnetic flux density applied to the conductor. The results of the loss calculation and the impact of the different contributions are then presented for the actual proposed magnet system configuration.
|Submitters Country||Italy, Switzerland|