Structural design and fabrication of the main magnet for multi-particle cyclotron

Abstract Addressing multiple important and urgent needs that have emerged recently, including the medical isotopes development and production, e.g., the therapy isotope 211At, and the PET isotopes 18F, 89Zr, 64Cu, etc., the China Institute of Atomic Energy (CIAE) has developed a multi-particle superconducting cyclotron for the production of H 2+ and α beam. It is expected to be completed by the end of this year. The main magnet of the SC cyclotron uses a compact monolithic design with complex geometry operating under high saturation conditions. Fabrication dimensions rigorously adhere to physical specifications, eliminating the tolerance in component assembly and achieving high structural symmetry, and thereby the precise field distribution through integrated machining. Each magnet unit employs a DT4-electrical pure iron configured with four sectors and a variable hill gap. To optimize magnetic field strength while decreasing manufacturing complexity and cost, a magnetic field self-shielding structure with a central compensated plate has been implemented. This paper further details chemical composition measurement, magnetic property annealing, mechanical structure design, tolerance analysis, and deformation studies, and concludes with the current engineering progress of the magnet system.