Upgrade of RFQ injector system for proton synchrotron at Shanghai Advanced Proton Therapy Facility
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摘要: 为实现质子治疗装置的国产化和小型化,基于已完成安装调试的上海先进质子治疗装置(APTR),开展质子治疗注入器系统的升级设计研究,利用PARMTEQM设计软件和快聚束策略,针对APTR同步加速器RFQ直线注入器进行动力学设计模拟。RFQ工作频率为325 MHz,流强18 mA,对从离子源引出的低能质子束流进行匹配俘获、横向聚焦、纵向聚束和预加速,引出能量为3.0 MeV。通过优化预注入器RFQ动力学设计方案和极头参数,有效避免参数共振,减小束流损失,使其整体传输效率达到98.0%,在水平和垂直方向上的发射度增长分别为1.2%和3.3%,出口束流满足下一级腔体的注入需求,开展设计模拟验证和相关冗余度分析,为质子同步加速器的治疗设备和直线注入系统提供参照依据。Abstract: The Shanghai Advanced Proton Therapy Facility (APTR) project, proposed by the Shanghai Institute of Applied Physics (SINAP) of Chinese Academy of Sciences, has finished in the commissioning stage. As the key component of APTR complex, the injector system is upgraded to accelerate proton beam to 7.0 MeV in the context of comprehensive localization and miniaturization. To pre-accelerate, longitudinally bunch and transversely focus the low-energy proton beam from ion source, a pre-injecting system Radio-Frequency Quadruple (RFQ) was designed. Based on fast bunching strategy, this RFQ, operated at 325 MHz, accelerates proton particles to 3.0 MeV. The phase advance has been taken into consideration, and parametric resonance has been carefully avoided by adjusting the vane parameters. The whole transmission efficiency has been optimized to 98.0% to meet the machining requirements and the emittance growth in horizontal and vertical directions are about 1.2%, 3.3% along the entire cavity. This paper mainly introduces the beam dynamics design schemes, main parameter selections, simulation results and tolerance analysis. It can provide important theoretical base for linear injection system of proton synchrotron-based therapy facility.
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Key words:
- proton therapy /
- linac injector /
- 4-vane RFQ /
- advanced proton therapy facility /
- fast-bunching
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表 1 RFQ直线加速器主要的设计要求
Table 1. Main parameters of the RFQ
parameters values units ion type proton − frequency 325 MHz pulse repetition rate 0.5~10 Hz output beam pulse length 40~100 μs output energy 3.0 MeV maximum duty factor 0.1 % input norm. RMS emittance 0.2 π·mm·mrad maximum output norm. RMS emittance 0.24 π·mm·mrad beam current 18 mA 表 2 频率接近325 MHz的RFQ装置的相关参数汇总
Table 2. Parameters of proton RFQ facilities with adjacent frequency around world
表 3 优化前后束流动力学设计参数对比
Table 3. Beam dynamics design results of the traditional and optimized design
parameters traditional design optimized design units frequency 325 325 MHz input energy 30 30 keV output energy 3.0 3.0 MeV beam current 18 18 mA inter-vane voltage 75 75 kV $\varepsilon _{{\rm{in}}}^{ {\rm{trans} },{\rm{norm} },{\rm{RMS} } }$ 0.2 0.2 π·mm·mrad minimum aperture 1.744 1.920 mm Kilpatrick factor 1.8 1.7 − cavity length 319.22 310.00 cm transmission eff. 97.5 98.0 % $\varepsilon _{ {\rm{out} } }^{x,{\rm{norm} },{\rm{RM} }S}$ 0.215 6 0.202 3 π·mm·mrad $\varepsilon _{{\rm{out}}}^{y,{\rm{norm}},{\rm{RMS}}}$ 0.221 5 0.206 6 π·mm·mrad $\varepsilon _{{\rm{out}}}^{z,{\rm{norm}},{\rm{RMS}}}$ 0.068 94 0.060 95 π·MeV·(°) -
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