基于BEM泊松方程求解的空间电荷效应数值模拟

 为了模拟强束流在加速器及其传输线中的行为，用C++语言开发了一种包含空间电荷效应的多粒子跟踪程序(PTP-SC)，它在经典的PIC方法基础上，基于边界元法(BEM)和非等距的网格求解泊松方程。束流在自由空间分布的仿真结果与解析结果保持较好的一致性。给出了一条注入线的模拟计算结果，并与ORBIT,TRACE 3-D的计算结果进行比对。结果表明：该程序与采用数值方法的ORBIT程序的计算结果有较好的一致性。该程序可用于直线加速器及回旋加速器中的空间电荷效应模拟。     

强流脉冲束在螺旋管透镜中的非线性传输计算

为计算强流脉冲束在螺旋管透镜6维相空间中的非线性传输,用Visual Fortran 6.5语言设计了一个计算程序,计算由漂浮空间、螺旋管透镜等元件组成的束流光学系统。程序在计算非强流脉冲束流的线性传输时,粒子的轨迹通过矩阵的直接相乘计算得出;程序在计算强流脉冲束流的非线性传输时,需要考虑束流中的空间电荷效应对束流传输的影响,在束流运动过程中,空间电荷场也在不断地变化,而且粒子运动的轨迹与空间电荷势又是相互依赖的,因此需要求得一个自洽的解,先把元件分成若干均等的区间,把电流分成若干等份,后采用束流电流迭代与元件区间迭代的计算方法。程序运行结束时,横向和纵向相图以及束流光学系统的束流包络线可以在微机屏幕上直观地显示出来。     

TOPOPIC对强流束流在周期FODO结构中的传输研究

粒子云网格(Particle In cell,PIC)方法是研究带电粒子在加速器中运动的关键工具之一。基于PIC算法,开发了模拟强流条件下的束流动力学模拟程序TOPOPIC(Trace of Particle Orbit with PIC method),并且利用TOPOPIC,研究了束流在四极铁周期结构(FODO)中的传输问题。结果表明,在强流条件下空间电荷效应显著地影响了束流的整体行为和单粒子的运动轨迹。最后比较了TOPOPIC程序和通用的BEAMPATH程序在相同条件下的计算结果,可以看到两个程序给出的模拟结果吻合得非常好,这表明TOPOPIC程序的计算结果是合理、可靠的。     

CYCIAE-100轴向注入线设计及中心区束流匹配

采用包含空间电荷效应的束流光学计算软件TRANSOPTR对CYCIAE-100回旋加速器轴向注入线进行设计,在综合考虑空间布局、元件选择、真空度、空间电荷效应、轴向磁场和造价等问题后,最终确定了轴向注入线的聚焦结构。将数值跟踪获得的真实磁场下螺旋偏转板传的输矩阵编写到TRANSOPTR程序中,从而实现了从离子源出口至偏转板出口的束流光学匹配。介绍了CYCIAE-100回旋加速器轴向注入线的设计思想、布局结构和束流光学计算结果,并给出了主要元件的设计结果。在确定中心区结构和对中轨道后,采用多粒子轨道跟踪的方法进行中心区束流匹配的研究,通过对数值模拟的结果进行椭圆拟合并结合解析公式计算得到注入点处匹配矩阵,为注入线的设计提供拟合条件。     

准周期聚焦–加速耦合系统的均温设计方法

强流质子直线加速器要求严格控制束流损失和束流发射度增长.理论已经证明,强的空间电荷作用在不同自由度之间的耦合,会因为其间的温度差异,通过束流的相干不稳定性,使束流发射度增长.因此,有必要按照均温的原则设计强流加速器.但是,由于质子直线加速器的各种加速结构均为准周期耦合系统,使得均温设计十分繁琐而难以达到完全均温.我们利用国际上通用的束流动力学软件TRACE3-D,给它补充了均温设计功能,通过与PARMILA程序的配合使用,可以方便地在加速器设计中实现均温条件.本文将介绍我们对TRACE3-D的修改补充,并以强流质子直线加速器设计实例,说明均温设计的必要性.     

双圆筒加速透镜中强流束传输的模拟

用矩阵法分析非强流束流与强流束流在双圆筒加速透镜中的传输,编写束流在双圆筒加速透镜等元件中传输的计算程序DCALENS.采用优化方法实现给定的光学条件,用迭代方法计算强流束传输获得自洽解.在不同束流流强条件下,用DCALENS程序进行模拟计算,并对模拟结果进行比较分析.结果表明:束流流强越大,束流包络曲线横向发散越显著,空间电荷力越强;束流流强大于2 A时,束流包络曲线发散明显.     

100MeV强流质子回旋加速器轴向注入系统和中心区物理设计

100MeV强流质子回旋加速器设计的引出质子束流强为大于200μA, 并计划提供脉冲束流. 轴向注入系统设计有两条注入线, 即1#和2#注入线. 1#注入线利用负氢束的中性化以解决强流连续束流的注入,为保证达到高中性化程度, 横向聚焦均采用磁元件; 2#注入线的设计目的主要是提供一定流强的脉冲化束流,由于脉冲化负氢束的中性化过程难以建立, 因此, 横向聚焦元件均为静电元件. 两条线合理的结构设计使得注入系统可方便切换运行模式. 采用包含空间电荷力的光学计算程序, 匹配不同中性化程度的注入束流光学特性, 匹配工作的重点在于高达40°的高频相位接收度. 从离子源出口到粒子加速前15圈的连续匹配计算结果表明: 所设计的注入系统可有效地控制束流包络, 减少束流损失; 中心区高的高频接收度使设计的100MeV质子回旋加速器具有加速强流负氢束的能力.     

强流束在二极磁场中传输的模拟计算

为了研究空间电荷力对束流在二极磁场中传输的影响,从理论上用矩阵法分析非强流脉冲束流与强流脉冲束流在二极磁场中的传输矩阵,编写了束流在二极磁场等元件中传输的计算程序。用Powell优化方法计算非强流束传输实现给定的光学条件,用迭代方法计算强流束传输获得自洽解。在不同束流流强条件下,运用该程序与其他程序进行了模拟计算,并对模拟结果进行了比较分析。模拟结果表明:束流流强越大,束流包络曲线横向发散越显著,空间电荷效应越强。     

强流脉冲高斯分布束在磁四极透镜中的非线性传输

用李代数方法分析了高斯分布下强流脉冲束在磁四极透镜中的非线性传输.在高斯分布下,束流的空间电荷势可利用Green函数算出,进而可以得到包含束流自场的粒子运动的Hamilton函数.再施加李变换,就可以得到粒子运动的各级近似解.本文给出二级近似下的结果,根据需要,还可以扩展到更高级近似.计算过程需要进行迭代,即根据每次算出的轨迹值,确定束团在三维实空间中的大小,然后再进行迭代,直到满足精度要求为止.     

强流脉冲束在静电加速管中传输研究及模拟计算

为了研究强流脉冲束流在静电加速管中的传输, 采用矩阵法分析了非强流脉冲束流与强流脉冲束流在静电加速管中的传输矩阵, 编写了束流在静电加速管等元件中传输的计算程序ACCT。 用优化方法实现给定的光学条件, 用迭代方法计算强流脉冲束流的空间电荷效应对束流传输的影响以获得自洽解。 在不同束流流强条件下, 利用ACCT、TRACE-3D和TRANSPORT等程序进行了模拟计算, 并对模拟结果进行了比较分析。 模拟结果表明, 提高加速电压比, 可以增强静电加速管的聚焦能力、 减少束流损失和提高传输效率。To study intense pulsed beam transfer in electrostatic accelerate tube, the matrix method was applied to analyze the transport matrixes in electrostatic accelerate tube of non-intense pulsed beam and intense pulsed beam, and a computer code was written for the intense pulsed beam transporting in electrostatic accelerate tube. Optimization techniques were used to attain the given optical conditions and iteration procedures were adopted to compute intense pulsed beam for obtaining self-consistent solutions in this computer code. The calculations were carried out by using ACCT, TRACE-3D and TRANSPORT for different beam currents, respectively. The simulation results show that improvement of the accelerating voltage ratio can enhance focusing power of electrostatic accelerate tube, reduce beam loss and increase the transferring efficiency.     

30MeV医用回旋加速器气体靶束流线的研制

中国原子能科学研究院于1994年研究建成我国第一台医用强流回旋加速器CYCIAE-30及配套放射性同位素生产线, 目前为了增加气体靶以生产新品种医用同位素, 在原有束流输运线的基础上开展了束流输运系统的升级改造方案设计, 包括束流线的总体布局考虑和光学设计, 并根据束流光学设计的结果, 进行了新增束流线上电磁元件的设计. 在物理设计的基础上, 还进行了施工设计以及各分系统的加工、调试、安装, 并以物理设计得到的参数为依据进行了束流调试, 靶上得到的束斑与理论值有较好的符合, 满足设计要求.     

Influence of radial magnetic field on emittance in the median plane at CYCIAE-100

A 75—100 MeV H- compact cyclotron CYCIAE-100 is being constructed at China Institute of Atomic Energy (CIAE). About 200 μA proton beam will be provided by CYCIAE-100. The imperfection of magnetic fields will remarkably affect the acceleration orbit and beam envelope in CYCIAE-100. The effects to the accelerating beam by the imperfection fields, especially the field components Br on the mid-plane will be analyzed in detail with tracking code COMA. Poles misalignment that causes magnetic imperfection will be described in the paper. According to the simulation results, the tolerance of the poles machining and assembly will be illustrated in this paper.     

Study on the effects of chromaticity and magnetic field tracking errors at CSNS/RCS

The Rapid Cycling Synchrotron (RCS) is a key component of the China Spallation Neutron Source (CSNS). For this type of high intensity proton synchrotron, the chromaticity, space charge effects, and magnetic field tracking errors between the quadrupoles and the dipoles can induce beta function distortion and tune shift, and induce resonances. In this paper, the combined effects of chromaticity, magnetic field tracking errors and space charge on beam dynamics at CSNS/RCS are studied systemically. 3-D simulations with different magnetic field tracking errors are performed by using the code ORBIT, and the simulation results are compared with the case without tracking errors.     

3D simulation of the ion-beam transport in bending magnets and electrostatic deflectors

The equations and algorithms for calculating the charged-particle-beam dynamics in bending magnets and electrostatic deflectors, which are used in the ion-beam transport lines and spectrometers, are presented. Calculations of the electromagnetic field 3D maps are illustrated. The value of the electromagnetic-field nonlinearities and their effect on the particle dynamics are analyzed. The simulation of the ion dynamics in the axial injection beam line of the DC-280 cyclotron and GALS spectrometer created at the JINR Laboratory of Nuclear Reactions (FLNR) is described.     

Physics design of CYCAIE-100

The design and construction of Beijing Radioactive Ion-beam Facility (BRIF) was started at China Institute of Atomic Energy -CIAE) in 2004. In this project, a 100 MeV high intensity cyclotron, CYCIAE100, is selected as a driving accelerator for radioactive ion beam production. It will provide a proton beam of 75—100 MeV with an intensity of 200—500 μA. The scheme adopted in this design, i.e., stripping the accelerated H-, makes the structure more compact and construction cost much lower. At present, the design for each system has been accomplished. This paper depicts the basic physics design of the machine, including its major structure and parameters, beam dynamics and each relevant system, e.g. basic structure of the main magnet, numerical simulation of the RF resonant cavity, axial injection system, central region, and study on crucial physics problems concerning the extraction and beam lines. The major problems encountered during the design of CYCIAE-100 are also summarized in this paper.     

Study of energy deposition and stripper temperature for CYCIAE-100

Nowadays high intensity proton accelerators are extensively applied, and this paper gives particular emphasis on CYCIAE-100, a 100 MeV high intensity compact cyclotron being constructed at CIAE. For accelerators of this type, the study is focused on how to improve the beam intensity. As for CYCIAE-100, the charge-exchange extraction is used to get protons. So it is crucial to enhance the lifetime of the stripping foil, which is largely determined by the energy deposition on it. For this cyclotron, due to the influence of the magnetic field, the electrons will spin near the foil and lose energy each time when they cross the foil. The energy deposition refers to all the energy deposition of protons and electrons. This paper stresses the stripper study of CYCIAE-100, in which the particle distribution on the foil is simulated and the energy deposition of the protons and electrons stripped from the H- ions are calculated. The temperature distributions are then calculated as a main reference for the foil design.     

Development of 2D particle-in-cell code to simulate high current,low energy beam in a beam transport system

A code for 2D space-charge dominated beam dynamics study in beam transport lines is developed. The code is used for particle-in-cell (PIC) simulation of z-uniform beam in a channel containing solenoids and drift space. It can also simulate a transport line where quadrupoles are used for focusing the beam. Numerical techniques as well as the results of beam dynamics studies are presented in the paper.      

Central region design for a 10 MeV internal ion source cyclotron

Internal ion sources are widely adopted in commercial cyclotrons used for short-life isotopes produc-tion. Without beam manipulation provided by the external beam injection line, the central region of this type of cyclotron is more sensitive and should be carefully designed. A design study and beam dynamics simulation for the central region of a 10 MeV compact cyclotron is presented. The OPERA3D/TOSCA code was used to calculate the electric field from a parameterized three dimensional (3D) central region model. With iterative structure optimizations of the central region, the beam centering and vertical focusing is well controlled, and the RF phase acceptance is around 25° A c++ code for beam simulation in the central region was developed and tested.