强流重离子加速器中获得高引出效率慢引出束的方法研究

Wide energy range and high intensity extraction beams of heavy ion accelerators are required for experiments in particle physics, nuclear physics, atomic physics, energy materials and other related research fields. In the case of resonant extraction for high intensity heavy ion accelerator, not only the extraction angular divergence can be enlarged, but also the shape and orientation of outgoing separatrix can be changed by the space charge effect. As a result, the extracted beam will be seriously lost at the electrostatic septum. Therefore, this project proposes a new scheme to achieve high efficiency for high intensity heavy-ion accelerators based on dynamic sweeping outgoing separatrix during RF-knockout slow extraction process. This new scheme is used to reduce the extraction angular divergence and has not been used in any existing heavy-ion accelerators in China, so it has to be modeled and deeply studied the beam dynamics. Then it’s necessary to find the sweeping function of outgoing separatrix. In addition, the influence of space charge effect on the beam distribution in phase space and the reason of beam-loss in the resonant extraction process also need to be investigated. And the particle tracking code has to be developed to simulate the whole slow extraction process, so the critical factor affecting the extraction efficiency and the corresponding solution can be found. Finally, the simulation results will be verified experimentally.

粒子物理、原子物理、原子核物理、新能源材料等学科领域的蓬勃发展，对重离子加速器提供宽能量范围与高流强的慢引出束要求越来越高。在强流重离子加速器共振慢引出中，束流空间电荷效应会导致束流引出角散增大，引出界轨形状与方向发生改变，在静电偏转板处将造成严重的束流损失。因此，本项目拟在RF-KO引出方式下采用引出界轨动态扫描的方法实现高效率束流慢引出的目标。该方法是一种减小束流引出角散以提高慢引出效率的新方法，在目前国内存在的重离子加速器中均未使用，需要对其建模并深入研究束流动力学，找到界轨的动态扫描函数。同时，需要深入探究强流空间电荷效应对束流相空间分布的影响和导致束流慢引出的损失机制，开发多粒子跟踪程序模拟束流慢引出的全过程，寻求影响束流慢引出效率的关键因素和解决方案，并对模拟结果进行实验验证。

粒子物理、原子物理、原子核物理、新能源材料等学科领域的蓬勃发展，对重离子加速器提供宽能量范围与高流强的慢引出束要求越来越高。在强流重离子加速器共振慢引出中，为了避免慢引出过程束流引出角散较大而在静电偏转板处将造成严重的束流损失，本项目提出了一种引出界轨动态扫描的新颖方法实现高效率束流慢引出。首先对引出界轨动态扫描进行了理论分析与数学建模，开发和完善了慢引出全过程动力学模拟平台SESP，并进行了多粒子跟踪模拟，填补了此类程序在国内的空白。同时，基于SESP平台研究了HIAF-BRing主要引出参数及空间电荷效应对慢引出束界轨的影响，为后期慢引出束调试与效率提高奠定了基础。此外，引出界轨动态扫描方法已应用到空间环境地面模拟装置 (SESRI) -300 MeV质子重离子加速器装置慢引出系统中，搭建了实验研究平台并开展了实验验证。在引出7 MeV/u 的209Bi32+时, 引出发射度为107 πmm.mrad，实验中采用引出界轨动态扫描与六极铁ramping相结合的新方法，慢引出效率提高了近3倍，达到了90%，满足了实验终端对粒子数的要求。新引出方法在不采用电子冷却的条件下，成功解决了低能超大发射度慢引出效率低的难题，实现了目前文献记载的最大发射度慢引出，具有重要的工程应用价值。