Design of superconducting magnets for high energy beam transport lines for proton cancer therapy

In proton cancer therapy, to overcome the size and performance limitations of conventional electromagnetic systems, we have designed a superconducting high-energy beam transport line that utilizes superconducting magnets to provide higher magnetic fields, thereby significantly reducing system size and enhancing efficiency. The transport line consists of six groups of superconducting magnets, each employing a discrete cosine theta (DCT) coil structure [1], [2], [3], [4], [5], comprising one curved dipole magnet and two quadrupole magnets, forming a Q-D-Q (quadrupole-dipole-quadrupole) configuration. The dipole magnet generates a central field of 2.77 T with a bending radius of 900 mm, while the quadrupole magnets have a gradient of 40 T/m. To ensure magnetic field quality, we developed a parametric model in CST and optimized the field characteristics, achieving an integral magnetic field uniformity of better than 0.01%. During rapid excitation, eddy current losses in metallic structures and AC losses in superconductors lead to temperature rise, which may trigger quenching. To mitigate this, we developed a detailed finite element model (FEM) in ANSYS and optimized the magnet’s cooling structure, ensuring that the maximum temperature rise is limited to 0.66 K over three operating cycles. Simultaneously, we established a 2D structural model to analyze the stresses in the magnet, confirming that the Von Mises stress is lower than the yield stress. Through these optimizations, a prototype was successfully fabricated to explore the manufacturing process of the Q-D-Q magnets. This work not only provides a technical foundation for future mass production but also offers critical technical reserves for the construction of superconducting Gantries.