切割磁铁作为同步加速器注入引出的关键部件之一，对磁场及切割板结构都有严格的要求。介绍了兰州重离子治癌装置(HIMM)同步加速器切割磁铁的设计情况，基于磁场优化软件OPERA，对切割磁铁磁场均匀度及杂散场的分布进行了详细的分析。根据磁场要求优化结构设计，完成了磁铁的加工。磁场测量结果分析显示，有效场区范围内磁场均匀度优于设计结果。同时通过对磁铁端部屏蔽处理，在环内侧管道处杂散磁场降到2 mT以内，满足物理设计要求。

Septum magnet is one of the most important devices for beam injection and extraction in circular particle accelerators. Because of the high-field requirements with thin septa and low stray field, the structure of septum magnet is very complicated. In this paper, the design of septum magnet is shown in detail. Based on the finite element software OPERA, the magnetic field homogeneity and stray field distribution are analyzed. The magnet’s fabrication is finished after structure optimal design. The measurement results show that the magnetic field homogeneity in good field region is better than the designed value. The stray field could reduce to 2 mT after shielding with high permeability magnetic material, which satisfies the physical requirements.