Magnetic design of downstream scanning magnets for a novel hadrontherapy gantry

Hadrontherapy utilizes accelerated ion beams to deliver precise and effective cancer treatments, depositing energy at specific depths while sparing healthy tissues. Gantries are large rotating structures that direct beams at various angles around the patient, improving dose conformity to tumors and the robustness of the treatment plan while minimizing radiation exposure to surrounding organs. While proton gantries are widespread and commercially available, the diffusion of carbon ion gantries is limited due to more demanding technological challenges and financial investments. This paper presents the magnetic design of the scanning magnets for the EuroSIG (European Superconducting Ion Gantry) project, aimed at developing a novel superconducting gantry for hadrontherapy. The chosen layout foresees the positioning of the scanning magnets downstream of the last bending section. This simplifies the production of the superconducting dipole but increases the complexity of the scanning system in terms of integrated fields, bending angles, and ramp rates. To address this challenge, analytical models and optimization tools were employed to achieve balanced configurations for the scanning magnets, improving compatibility with power converters. Three-dimensional numerical simulations were implemented to evaluate and improve the steady-state field quality of horizontal and vertical scanning magnets. Particle tracking was used to validate the effective beam deflection in both magnets and assess beam position errors at the isocenter. Furthermore, quasistatic simulations were carried out to evaluate integral field errors due to the hysteretic behavior of the yoke alloy. Continuing the analysis of dynamic phenomena, the generation of eddy currents in the laminated yoke was investigated, highlighting the delay of the generated field with respect to the imposed current profile. The studies reported in this manuscript confirmed the design’s feasibility, posing a solid base for the construction of the first scanning magnet prototype.