Development of extraction system for 50 MeV proton cyclotron

Built by the China Institute of Atomic Energy for the National Space Science Center, the HuaiRou Proton Cyclotron Facility (HRPCF) consists of a 50 MeV proton cyclotron, beam lines and experimental terminals. As the world’s first compact medium-energy proton cyclotron for space radiation environmental effect tests, it is designed for ground-based simulation of space proton radiation environments, adopting the stripping foil method for proton beam extraction. This study develops a stripping foil system, covering beam dynamic simulation, foil position optimization, multi-energy beam stripping analysis and switch magnet parameter calibration. The overall design integrates mechanical structure, control system, transient temperature field simulation of the stripping foil and switch magnet design. Dedicated codes are adopted for beam dynamic simulation. A compact switch magnet is embedded in the cyclotron main magnet yoke to reduce beam energy dispersion caused by beam drift, magnetic field asymmetry and edge effects, with magnet performance simulated via Poisson software. Transient temperature field simulation is conducted to analyze the foil’s thermal characteristics during beam extraction. A motorized positioning mechanism with a double-layer radial shaft is designed, where the inner shaft is equipped with a stepper motor and magnetic fluid seal drives foil rotation through bevel gears. In July 2022, 30-50 MeV proton beams with a current density of 2 nA/cm² were stably output to a 150 mm-diameter quartz target after brief commissioning. The 200 mm×200 mm beam spot shows horizontal and vertical non-uniformity of 3.22% and 6.01% respectively, with well-controlled energy dispersion. Beam energy can be continuously adjusted from 30 MeV to 50 MeV by tuning foil position. The terminal has supported dozens of multi-institute experiments including single event effect tests and irradiation damage tests. The rationally designed mechanical and control systems realize an engineering-qualified stripping foil and beam extraction system with simple operation and precise positioning. Consistent with design specifications, the HRPCF extraction system achieves long-term stable operation, providing reliable support for spacecraft space proton radiation ground simulation tests.