Design Of A Canted-Cosine-Theta Superconducting Magnet Applied To Proton Therapy

Proton therapy is one of the most advanced and precise cancer treatment methods at present.The Gantry is one of the core components of proton therapy equipment,which projects the proton beam onto a tumor from different angles.The weight of the gantry with normal conducting magnets is usually more than 150 tons,which puts forward high requirements for the design,processing and fabrication.At present,the realization of light-weight gantry is of great significance for the promotion and application of proton therapy.In this paper,A Canted-Cosine-Theta(CCT)superconducting magnet applied to the lightweight proton therapy gantry is studied.Compared with the normal gantry,the weight of the gantry with CCT magnet as the curved magnet can be reduced by about an order of magnitude.In addition,since the superconducting CCT magnet can produce higher magnetic field,for the proton beam with the same magnetic stiffness,the deflection radius of the magnet can be significantly reduced,thus reducing the radius and volume of the gantry.In this paper,a complete and reliable program for the design and calculation of CCT magnet is established,and a magnetic field optimization scheme is proposed.On this basis,the optimization design of CCT magnet applied to superconducting gantry is carried out.The main contents of this paper include:(1)Due to the complex structure of CCT coil,there are time-consuming problems in the modeling and magnetic field analysis of OPERA-3D and other finite element software,which affect the magnet design and iterative optimization.In this paper,the CCT calculation model based on the Biot-Savart principle is established by using the line current integration method(Hereinafter referred to as BS method),and the calculation time-consuming problem is solved.Based on these,a multi-line high-precision calculation model is adopted,which significantly improves the magnetic field calculation accuracy of CCT model.By comparison,the results of BS method are consistent with those of OPERA-3D,and the calculation efficiency is improved significantly.(2)The curved CCT magnet applied to the beam deflection section of the gantry can significantly reduce the weight and size of the magnet.Due to the shift of the magnetic center,the curved CCT magnet contains the inherent magnetic field distortion under the cylindrical harmonics.Therefore,this paper uses the combined-function curved CCT coil path to optimize the magnetic field quality,searching for the optimal multipole magnetic field component coefficient in the path equation of combined-function CCT coil by iteration to compensate the redundant higher-order harmonic components in the initial model.(3)An Alternating-Gradient Canted-Cosine-Theta superconducting magnet is adopted in the superconducting gantry scheme proposed by the research team.In this paper,the design of the 67.5°AG-CCT magnet is carried out according to the parameters requirements proposed by the scheme.After the optimization of magnetic field,the uniformity increases significantly and the higher harmonic components are suppressed.The magnetic field distribution meets the expectation.The superconducting wire is selected according to coil magnetic field and current.Finally,combined with the Lorentz force calculation and ANSYS software,the preliminary structure design and analysis of the winding mandrel are completed.