Field Mapping System Design for the Superconducting Cyclotron CYCIAE-230

A superconducting cyclotron named CYCIAE-230 is designed and under construction at the China Institute of Atomic Energy, Beijing, China, to provide a 230-MeV proton beam for cancer therapy. The cryogenic system has been completed and the machining of the magnet will be finished soon. The shimming procedure will be performed to obtain the final isochronous field, which requires the field measurement precision to be 5 × 10
^–5
. A search-coil sensor based mapping system was developed to satisfy the measurement accuracy requirements, including a nuclear magnetic resonance probe to precisely measure the field at the cyclotron center and a moving search coil to obtain the field differences. Moreover, a Hall probe is integrated in the system to verify the field data. The system allows the probe motion and data acquisition to be performed automatically. In this paper, the field mapping requirements are listed, the design and calibration of the coil is described, and the field mapping system, including mechanical structure and control system, is presented in detail.