Optimization and Experiment Progress on Electrostatic Deflector of SC200 Superconducting Proton Cyclotron

Proton therapy is one of the most advanced cancer treatment methods, the study of proton therapy equipment has received increasing attention in China. Hefei CAS Ion Medical and Technical Devices Co., Ltd. (HFCIM) is developing a proton medical device based on the superconducting proton cyclotron (SC200). The extracted proton beam energy of SC200 is designed to be 200 MeV and the beam current is higher than 400 nA. The electrostatic deflector (ESD) is used as the key extraction component to bend the proton beam from the track. Due to the volume limitation of the cyclotron, the ESD shall provide an electrical field up to 150kV/cm to obtain a higher extraction efficiency. However, the extremely high-intensity electric field brings great challenges to the structure optimization, the fabrication technology, and the commission strategy of ESD. HFCIM has completed the engineering design, the material selection, and the technique exploration of the whole ESD system of SC200, and several prototypes have been manufactured. A testing setup with the maximum 1.6 T magnetic field background and the 10−4 Pa magnitude vacuum condition has been established. The commission and the aging experiment is proceeding. From the latest testing results, the ESD can reach to an electrical field of 150 kV/cm, but the stability and the repeatability still need to be improved. Meanwhile, the research of the surface modification of the ESD electrode is in progress, TiNx will be grown on to the electrode surface by the high temperature annealing, which may limit the electron emission.