用于硼中子俘获治疗的强流质子回旋加速器中心区结构优化设计

中国原子能科学研究院目前正在研制用于硼中子俘获治疗（BNCT）的强流质子回旋加速器，该加速器设计引出能量14 MeV、质子束流强大于1 mA。相比引出流强为400 μA的PET回旋加速器，BNCT强流质子回旋加速器对中心区相位接收度和轴向聚焦的要求更高。为实现mA量级的束流的加速和引出，BNCT强流质子回旋加速器采取了增加负氢束流注入能量、增大磁铁镶条孔径、使用用于增大Dee盒头部张角的阶梯状结构及调整加速间隙的入口和出口高度等一系列中心区结构优化设计，有效地提高了中心区的相位接收度，改善了轴向电聚焦。在新的离子源注入能量下通过数值计算得到实测场下的轴向电聚焦和间隙高度的关系，选取合适的间隙高度获得最佳的轴向聚焦，从而确定了mA量级束流的注入和加速的中心区结构。同时在设计中考虑空间电荷效应的影响，计算了不同流强下的束流尺寸变化。中心区结构在实测磁场下的优化设计计算结果表明，BNCT强流质子回旋加速器中心区的束流对中好于0.5 mm，相位接收度大于40°，中心区最高可接收流强3 mA。目前，新的中心区结构已进入机械加工阶段。

Structural Optimization Design on Central Region of High Intensity Proton Cyclotron for Boron Neutron Capture Therapy

A high intensity proton cyclotron is under construction at China Institute of Atomic Energy for boron neutron capture therapy (BNCT), whose current is larger than 1 mA and extracted beam energy is 14 MeV. Compared with 400 μA beam current PET cyclotron, larger phase acceptance and better axial focusing are required for BNCT high intensity proton cyclotron. To accelerate and extract the milliampere-scale current, a series of optimizations were adopted, such as increasing the energy injected by negative hydrogen beam, increasing the aperture of shimming bars, using stepped structure to increase the head angle of Dee tip, and adjusting the height of entrance and exit of acce-leration clearance, which lead larger phase acceptance and better axial electric focusing. Axial focusing with different heights of Dee gaps was acquired by numerical calculation to adopt the optimal heights. The space charge effect was concluded in calculation and beam sizes at different currents were simulated. The simulation at measured magnetic field shows that the beam centering is better than 0.5 mm, the phase acceptance is larger than 40° and the 3 mA beam can be accelerated. The new central region is being machined at present.