Preliminary Design of Superconducting Gantry Magnet for Miniaturized Heavy-Ion Facility

In order to improve the efficiency of cancer treatment, Lanzhou Ion Therapy Company, Ltd. (LANITH) proposed a miniaturized medical heavy-ion therapy facility. The gantry of the therapy facility is composed of six 45 degree combined function magnets, which are used to generate a dipole field (3.312 T) and a quadrupole field (11.5 T/m) with a good field region of no less than 60mm. The quadrupole coil is distributed on both sides of the dipole coil, and the maximum ramping rate of the magnetic field is 0.6 T/s. The magnet adopts the Discrete Cosine Theta (DCT) geometry, which is wound with six-around-one superconducting cable. Since the gantry is continuously rotating during the treatment process, the design of conduction cooling is required. Temperature rising inside the coil caused by high ramping speed will lead to quench, the design of cooling structure must be taken into consideration to avoid the risk. This article first illustrates beam optics and the electromagnetic design of the magnet, then the theoretical calculation of AC loss (including coil AC loss, Eddy current loss in mechanical structure) and quench protection design. By optimizing the coil cooling structure, reducing the influence of the loss on the magnet, and using quench-back quench protection design, the superconducting magnet will work safely and stably during continuous treatment.