Commissioning of a superconducting AVF cyclotron for proton therapy

A 230 MeV superconducting azimuthally varying field (AVF) cyclotron SC230 was developed by Sumitomo Heavy Industries, Ltd. Its weight is 65 t, which is 0.3 times that of our previous cyclotron model. The size was reduced by high magnetic field using cryogen-free superconducting coils. In addition, the maximum beam current is over 1 μA. The total power consumption of its system is less than 200 kW. In this cyclotron, some challenging designs, such as sectors with a narrow gap and large spiral angle, two dees with low power consumption and beam extraction using the precessional extraction method, were adopted. The fabrication of each component, including the magnet, has been reported in the development of the cyclotron. The cyclotron was moved to a new test site and pre-commissioning tests were conducted in 2020. The beam-commissioning test started at the end of 2020, and the first extracted beam was successfully observed in July 2021. In this paper, the processes and results of the beam commissioning that took place between 2020 and 2021 and the basic performance of the first beam are reported. (author)