Design and Construction of the Main Magnet for a 230-MeV Superconducting Cyclotron

For the applications of proton therapy and proton irradiation, and based on the R&D starting from 2009, a construction project of a 230-MeV superconducting cyclotron (CYCIAE-230) was launched at the China Institute of Atomic Energy in January 2015. A compact main magnet design with warm iron yokes and a superconducting coil system is adopted to reduce the size and, consequently, to lower the construction and operation cost of the cyclotron. In this paper, the physics design, along with the mechanical design of the main magnet, including the structure of the main magnet is described in detail; then, the construction progress and the B-H curve measurement results of the warm iron over the magnetic saturation region are outlined; the R&D of the superconducting coils system and the design of the field mapping system are also briefly introduced.