BRing中电荷交换引起的束流损失分布模拟计算
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摘要
在强流重离子加速器运行中,带电粒子与真空管道中的残余气体分子相互作用发生的电荷交换反应是影响重离子束流寿命的关键因素。这种电荷交换过程导致的束流损失将解吸出真空管壁上吸附的气体分子,进而引起真空压力的动态变化,将严重影响加速器的稳定运行和最终束流引出流强。中国科学院近代物理研究所将在广东省惠州市建造的强流重离子加速器装置(High Intensity heavy-ion Accelerator Facility,简称HIAF)利用增强器(Booster Ring,简称BRing)提供束流流强高达2×10~(11)ppp的~(238)U~(35+)用于核物理及原子物理等实验研究。对强流重离子加速器BRing中~(238)U~(35+)束流发生电荷交换反应,损失一个电子成为~(238)U~(36+)的过程进行了追踪模拟,计算得到了U~(36+)损失前的运动径迹和全环粒子损失位置分布,模拟结果显示U~(36+)受到色散元件的影响,将集中损失在位于二极磁铁后的漂移节区域中。基于模拟结果,在束流损失位置处设计安装由低解吸率材料制作的准直器,优化设计后的准直效率高达95%以上;并模拟计算了有无准直器时真空压力和束流流强的变化,安装准直器后BRing的平均真空度变化小于10%,将确保BRing加速器的稳定运行。
During heavy ion accelerator operation, the charge exchange effect between ions and residual gas molecules is the key factor to influence beam lifetime. The charge exchange process has ions lost on the wall and leads to a dynamical vacuum change, which will seriously affect the accelerator operation and reduce the extraction beam intensity. The Institute of Modern Physics' future project, called High Intensity heavy ion Accelerator Facility(HIAF), will be built in Huizhou city, Guangdong Province, China. The Booster Ring(BRing)will provide 2×11 ppp~(238)U~(35+) for nuclear physics experiments. This article studies the track of particle U~(36+) before impacting on the wall, which is the reference particle U3~(35+) losing one electron, and gets the U~(36+) loss distribution along the BRing. The simulation result shows that U~(36+) will be influenced seriously by dispersion elements, and will be lost in the drift sections after the dipoles. Collimators made out of materials with low desorption will be installed in the particles lost positions. The collimator efficiency after optimization can be larger than 95%. It also shows BRing average pressure change and beam intensity change between collimators on and off. The result points out that the BRing average pressure change will be less than 10% with collimators on, which makes BRing operate stably.
During heavy ion accelerator operation, the charge exchange effect between ions and residual gas molecules is the key factor to influence beam lifetime. The charge exchange process has ions lost on the wall and leads to a dynamical vacuum change, which will seriously affect the accelerator operation and reduce the extraction beam intensity. The Institute of Modern Physics' future project, called High Intensity heavy ion Accelerator Facility(HIAF), will be built in Huizhou city, Guangdong Province, China. The Booster Ring(BRing)will provide 2×11 ppp~(238)U~(35+) for nuclear physics experiments. This article studies the track of particle U~(36+) before impacting on the wall, which is the reference particle U3~(35+) losing one electron, and gets the U~(36+) loss distribution along the BRing. The simulation result shows that U~(36+) will be influenced seriously by dispersion elements, and will be lost in the drift sections after the dipoles. Collimators made out of materials with low desorption will be installed in the particles lost positions. The collimator efficiency after optimization can be larger than 95%. It also shows BRing average pressure change and beam intensity change between collimators on and off. The result points out that the BRing average pressure change will be less than 10% with collimators on, which makes BRing operate stably.
引文
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