重离子治癌装置4 MeV/u IH型漂移管直线注入器的动力学设计

基于KONUS束流动力学理论，完成了一台工作频率为162.5 MHz、占空比为1%的交叉指型漂移管直线注入器（IH-DTL）的动力学设计。该IH-DTL内置两套三组合四极透镜，共有41个加速单元，可为同步加速器提供流强400 eμA、能量4 MeV/u的C4+束流。在动力学设计过程中着重对每个加速间隙的同步能量偏差、注入相位和间隙电压等参数进行优化，使得该IH-DTL的横向归一化RMS接收度达到0.24 πmm·mrad，且横纵向归一化发射度增长小于10%，有利于提高同步环的注入效率。然后根据动力学设计的结构参数进行IH-DTL的高频仿真计算，将得到的三维电磁场分布导入PIC粒子跟踪程序中进行束流动力学模拟。动力学模拟结果显示，束流在IH-DTL出口的横向自然发射度小于13 πmm·mrad，达到了同步环的注入要求，而且在7%的垂直二极场分量下，束流中心的横向偏移在±0.5 mm以内，整体的束流传输效率高于99%。 An interdigital H-mode drift tube linac (IH-DTL) with KONUS beam dynamic has been designed, which operation frequency was chosen 162.5 MHz. This IH-DTL consists of 41 accelerating cells and two quadrupole magnets triplets, can provide the C4+ with the current of 400 eμA and energy of 4 MeV/u for the synchrotron. In the beam dynamic design, the synchronous particle energy, inject RF phase and the acceleration voltage of each gap are optimized carefully to make the transverse normalized RMS acceptance of the IH-DTL to be 0.24 πmm·mrad and the beam emittance growth small than 10%. Then the RF structure was designed and the 3D electromagnetic field was imported into the PIC particle tracking code for the beam dynamic simulation. The transverse beam emittance at the exit of the IH-DTL is small than 13πmm·mrad which meets the injection requirement of the synchrotron. What is more, under the 7% vertical dipole fields component, the offset between the beam center and the drift tube's axis is ±0.5 mm at most. The transmission efficiency of the IH-DTL is higher than 99% for the whole beam in the acceptance.