Development of 16MeV compact cyclotron RF system with solid-state amplifier and fully digital controller

Abstract State Power Investment Corporation (SPIC) developed a 16 MeV compact cyclotron for producing medical radioactive isotope 18 F. The cyclotron radio frequency (RF) system's architecture and hardware design as well as the control algorithms and software design are discussed and tested in this paper. The RF system includes a RF cavity, a 16 kW 38.44 MHz RF solid-state amplifier (SSA), power transmission line systems and a fully digitalized low-level RF (LLRF) unit. The RF cavity consists of two dees, a coarse tuning plate, a fine-tuning plate, a RF feeding port, a RF pickup port with a compact size and relatively low power dissipation. The RF amplifier adopts an all-solid-state compact design without any circulator as this cyclotron operates at a relatively lower frequency, and cooperates with the digital LLRF system to realize RF power feed-in at low frequency. By using LLRF featuring functions of tuning control, amplitude control, and phase control, the RF system achieved cavity frequency tuning, closed loop amplitude and phase regulations of the cavity. Through a fully digitalized low-level design, the system realized parameterized configuration capabilities. By adopting non-IQ RF direct sampling, the efficient noise suppression control was achieved. To reduce the maintenance and operational complexity of the system, the system adopted a novel hybrid frequency tuning algorithm that could enable rapid tuning control of cyclotron cavity. Based on a brand-new parameterized automated RF running process, the system realized automatic RF power-up procedure. In beam commissioning, the measured amplitude stability of the RF system was better than 0.1% and phase stability was better than 0.3 ∘ . The design and performance test results of the RF system will be presented in this paper.