First beam extraction from a superconducting azimuthally varying field cyclotron for proton therapy

A 230 MeV superconducting azimuthally varying field (AVF) cyclotron SC230 was developed by Sumitomo Heavy Industries Ltd., Japan. With a yoke diameter, height and weight of 2.8 m, 1.7 m and 65 t, respectively, it is currently the most compact isochronous cyclotron for proton therapy. Size reduction was achieved by a high magnetic field using cryogen-free superconducting coils. It adopts not only a superconducting magnet, but also sectors with a narrow pole gap and large spiral angle, two dees with low power consumption, and beam extraction using the precessional extraction method. It has a maximum beam current of 1 μA. The total power consumption of its system is lower than 200 kW. After each component, including the magnet, was fabricated, the cyclotron was moved to a new test site, and a vacuum test and conditioning of some components were conducted. The beam commissioning started, and the first extracted beam was successfully observed. In this paper, the processes and results of the beam commissioning and the basic performance of the first beam are reported.