High-energy proton microbeam facilities are powerful tools in space science, biology and cancer therapy studies. The primary limitations of the 50 MeV proton microbeam system are the poor beam quality provided by the cyclotron and the problem of intense scattering in the slit position. Here, we present an optical design for a cyclotron-based 50 MeV high-energy proton microbeam system with a micron-sized resolution. The microbeam system, which has an Oxford triplet lens configuration, has relatively small spherical aberrations and is insensitive to changes in the beam divergence angle and momentum spread. In addition, the energy filtration included in the system can reduce the beam momentum spread from 1 to 0.02%. The effects of lens parasitic aberrations and the lens fringe field on the beam spot resolution are also discussed. In addition, owing to the severe scattering of 50 MeV protons in slit materials, a slit system model based on the Geant4 toolkit enables the quantitative analysis of scattered protons and secondary particles. For the slit system settings under a 10-micron final beam spot, very few scattered protons can enter the quadrupole lens system and affect the focusing performance of the microbeam system, but the secondary radiation of neutrons and gamma rays generated at the collimation system should be considered for the 50 MeV proton microbeam. These data demonstrate that a 50 MeV proton microbeam system with a micron-sized beam spot based on a cyclotron is feasible.

高能质子微束设施是空间科学、生物学和癌症治疗研究的强大工具。50 MeV质子微束系统的主要局限性是回旋加速器提供的光束质量较差以及狭缝位置的强烈散射问题。在这里，我们提出了一种基于回旋加速器的具有微米级分辨率的 50 MeV 高能质子微束系统的光学设计。该微束系统采用牛津三合透镜配置，球面像差相对较小，并且对光束发散角和动量扩散的变化不敏感。此外，系统中包含的能量过滤功能可以将光束动量扩散从 1% 减少到 0.02%。还讨论了透镜寄生像差和透镜边缘场对束斑分辨率的影响。此外，由于50 MeV质子在狭缝材料中的严重散射，基于Geant4工具包的狭缝系统模型能够对散射质子和次级粒子进行定量分析。对于10微米最终束斑下的狭缝系统设置，很少有散射质子可以进入四极透镜系统并影响微束系统的聚焦性能，但准直系统处产生的中子和伽马射线的二次辐射应该是考虑用于 50 MeV 质子微束。这些数据表明，基于回旋加速器的具有微米级束斑的 50 MeV 质子微束系统是可行的。对于10微米最终束斑下的狭缝系统设置，很少有散射质子可以进入四极透镜系统并影响微束系统的聚焦性能，但准直系统处产生的中子和伽马射线的二次辐射应该是考虑用于 50 MeV 质子微束。这些数据表明，基于回旋加速器的具有微米级束斑的 50 MeV 质子微束系统是可行的。对于10微米最终束斑下的狭缝系统设置，很少有散射质子可以进入四极透镜系统并影响微束系统的聚焦性能，但准直系统处产生的中子和伽马射线的二次辐射应该是考虑用于 50 MeV 质子微束。这些数据表明，基于回旋加速器的具有微米级束斑的 50 MeV 质子微束系统是可行的。