A 75 MeV cyclotron is currently under development at the China Institute of Atomic Energy (CIAE). This machine is designed to extract a beam with a rated power exceeding 60 kW for the production of medical radioisotopes, such as ⁶⁸Ge, ²²³Ra, and ²²⁵Ac, aiming to meet the growing domestic demand for diagnostic and therapeutic radionuclides. This paper addresses key challenges and solutions in the design and computational analysis of the main magnet. The magnet poles adopt a structural design scheme featuring integrated straight-edged sectors with a slight spiral angle at the trailing edges. The isochronous magnetic field distribution is achieved through an axial shimming method. Magnetic field optimization was performed using the numerical simulation software OPERA-3D, thereby enhancing the acceleration efficiency of the cyclotron. Furthermore, deformation simulation and mechanical structural optimization were carried out for the main magnet. Under the premise of ensuring overall performance, the deformation of the main magnet, which has a diameter of 4.4 meters and a weight of 130 tons, was controlled within acceptable engineering tolerances.

The neutron yield of the neutron source based on the 18MeV/1mA high-intensity cyclotron developed by the China Institute of Atomic Energy (CIAE) has reached 7×10^13 n/s and has been successfully applied in high-resolution neutron imaging and Boron Neutron Capture Therapy (BNCT) experiments. Precise and quantitative start-to-end beam dynamics simulations facilitate a better understanding of the complex beam dynamics behavior of high-intensity beams, which is one of the key technologies for high-intensity cyclotrons. The beam dynamics simulation technology for cyclotrons is relatively mature. However, it is typically implemented independently in each subsystem. During the simulation process, assumed initial conditions are introduced multiple times, making it difficult to obtain quantitative results and carry out a global optimization design of beam dynamics. Start-to-end beam dynamics simulation is used in the 18MeV/1mA high-intensity cyclotron. It quantitatively simulates the beam dynamics behavior of high-intensity beams in each subsystem, including the injection line, spiral inflector, central region, acceleration region, extraction region, and uniform beam transport line.