中国散裂中子源加速器束流引出调试和束损优化

引出系统是中国散裂中子源快循环同步加速器的核心组成部分，对束流精确打靶和加速器稳定运行具有重要意义。首先，详细介绍了快循环同步加速器的引出系统和束流引出方案，重点介绍了一些引出系统相关的关键技术。其次，对引出束流调试进行深入研究，包括纵向束流调试、横向束流调试、引出束流分布优化等，其中纵向束流调试主要针对8个引出Kicker定时进行精确标定，横向束流调试主要指Lambertson型磁铁、8个Kicker磁铁、高能输运线模式的匹配设置。最后，对引出束流束损进行深入研究和针对性优化，探索引出束流损失的各种来源，对Lambertson型磁铁漏场、引出束团长度、Kicker波形平顶、Kicker波形变化进行深入研究并对一些新的测量方法进行详细论述。同时，对Lambertson型磁铁入口产生超大辐射热点的现象进行深入研究，寻找其产生大量束流损失的根源，并提出最终解决方案，降低引出束流损失和辐射剂量，使其满足加速器运行要求。     

APTR质子同步加速器RFQ直线注入器的优化设计

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。     

重离子治癌引出BUMP电源控制器设计

引出凸轨(BUMP)电源是负责医用重离子加速器束流引出的关键设备,其电流上升的同步性影响束流的引出效率,而电流波形的多样性与治疗模式和治疗精度密切相关。要在凸轨磁铁(0.2~0.4 mH)上产生1~5 ms上升且精确同步的励磁电流,并确保电流的跟踪性和波形的多样性,采用了实时调整强励电压及基于特征参数的电流波形控制方法。本文介绍了基于Inter公司SoC(System-on-a-Chip)技术的引出BUMP电源数字控制器软硬件设计,并首次应用到医用重离子加速器装置,经过现场验证,在不同的凸轨磁铁上产生了1~5 ms同步变化的电流,同时保证了电流上升时期的跟踪精度(>5 s),达到了设计要求。     

医用重离子回旋加速器引出系统设计

紧凑型回旋加速器作为重离子医学专用装置同步加速器的注入器,其引出系统设计所用的磁场为TOSCA模型计算磁场。通过单粒子轨道计算确定引出系统的元件类型及基本参数;通过多粒子跟踪确定最终的元件参数和束流参数。为了提高引出效率,改善引出束流品质,在引出位置磁场梯度较大的位置,安放了一块C型磁铁,以改善此处的磁场梯度。同时,为了消除此C型磁铁对主磁场的影响,在此区域安放了一对线圈。计算结果表明引出系统的设计能够保证引出束流的强度和品质符合同步加速器的要求。     

兰州重离子加速器冷却存储环慢引出控制系统

兰州重离子加速器冷却存储环为了进行深层重离子治疗肿瘤的实验,需要长时间、均匀地慢引出束流至高能束运线,以满足深层重离子治疗肿瘤的束流要求。慢引出控制系统采用加速器控制系统的同步时间信号来进行同步控制以实现整个过程控制;当加速器控制系统的同步事例的同步触发信号进行触发控制以及数据切换（频率值、tune值、电压幅值）,波形发生器通过这三个数据信息产生相应的波形及进行放大器放大并控制静电偏转板以实现束流RF-KO方式慢引出。慢引出控制系统的同步事例接收器主要由FPGA与光纤接口组成,实现同步事例的高速稳定传输与强抗干扰性。深层重离子治疗肿瘤的正常运行以及冷却存储环已实现104 s超长周期的慢引出实验表明,慢引出控制系统能实现实验束流需求的慢引出。     

SFC新引出系统的物理设计研究

兰州重离子加速器(HIRFL)是一个回旋加速器组合系统. 它的注入器是K=69的扇聚焦回旋加速器.在十多年运行过程中, 曾做过两次较大的改进, 使加速的束流种类及流强都有了显著的改善.但由于SFC的引出效率比较低, 只有30%左右, 一方面损失了大量束流, 另一方面许多束流损失在引出静电偏转板上, 造成了大量出气, 破坏了真空, 难以维持长期大束流运行. 文章重新对SFC引出系统进行了物理设计研究, 在真实磁场的基础上做了大量计算工作, 得到了一个新的引出 系统方案.     

上海光源直线加速器的能量反馈控制

海光源恒流注入的运行模式,需要直线加速器提供持续、稳定和高品质的束流。阐述了八条形电极束流位置探测器(BPM)的工作原理及其对直线加速器至增强器低能运输线的束流进行能散的测量,并以（微波）幅度或相位作为调节参数,采用比例积分(PI)控制算法对束流能散进行反馈控制,实现了束流能量的长期稳定性,保证了直线加速器束流的高效率注入。     

中国散裂中子源注入系统电切割磁铁物理设计

利用OPERA/TOSCA大型有限元分析软件对中国散裂中子源/快循环同步环（CSNS/RCS）注入系统的直流C型特种电切割磁铁进行了2维/3维磁场计算和设计,通过放置1 mm厚的DT4铁磁性屏蔽板,可将循环束流轨道上的边缘漏场比降低至2.610-4,大大减小了切割板外侧的边缘漏场对循环束流动力学的影响。另外,对该类型切割磁铁的线圈做了详细的水冷计算,以保证磁铁能在适当的温度下运行。结果表明,无论从物理上还是工程上,该类型磁铁完全可以满足CSNS/RCS注入系统物理设计以及长期稳定运行的要求。     

基于射频功率调节的负离子源束流反馈控制研究北大核心CSCD

基于射频负离子源的中性束注入系统是高功率长脉冲(稳态)运行中性束注入系统的最佳选择。负离子源是中性束注入系统的核心部件,需要实现稳定的负离子束引出和加速。在负离子源的运行过程中引出负离子电流会发生变化,尤其在长脉冲、高能量运行条件下会更加明显,因此无法满足稳定运行的要求。为了实现引出束流的稳定引出,开展了束流反馈控制研究,研发了一套基于射频功率调节的束流反馈控制系统,并将束流反馈控制系统应用在射频负离子源测试平台,开展了束流反馈控制测试。测试结果表明束流反馈控制系统能够实现对束流的实时反馈调节以获得束流的稳定引出,验证了基于射频功率调节的束流反馈控制的可行性,为高功率射频负离子源的研制提供支持。     

CSNS/RCS中的阻抗和束流不稳定性

中国散裂中子源（CSNS）的快循环同步加速器（RCS）是一台强流质子加速器,其束流平均功率达到100 kW。在此强流加速器中,真空部件的阻抗是引起束流不稳定的主要原因,它严重限制了束流强度及品质。对CSNS/RCS设计中的各种真空部件阻抗进行了详细计算,并以计算结果为出发点,理论分析了各种不稳定性强弱,确定了各种不稳定性发生的阻抗阈值,为真空部件结构设计提供了参考。对比较严重的电阻壁阻抗,采用阻抗壁尾场模型进行跟踪模拟,得到不稳定性增长率与理论计算值符合较好。自然色品有助于束流稳定,加入自然色品后模拟,电阻壁不稳定性消失。     

CSR纵向束团压缩腔研究

针对兰州重离子加速器冷却储存环的发展目标,为了满足高能量密度（涉及重离子驱动惯性约束核聚变新能源）等物理研究的需要, 使用三维电磁场计算程序MAFIA研究了一种新型的适用于CSR的纵向束团压缩腔。 此纵向束团压缩腔采用高磁导率软磁合金材料进行加载,相比于铁氧体加载的高频腔, 可以得到高的电场梯度。以250 MeV/u的238U72+离子为例进行了模拟计算, 得出了此纵向束团压缩腔的工作频率为1.15 MHz, 峰值工作电压为80 kV, 由两个1/4波长同轴谐振腔组成, 每个谐振腔峰值工作电压为40 kV,能够满足在CSR上进行纵向束团压缩的要求。 The scheme of longitudinal bunch compression cavity for the Cooling Storage Ring(CSR) is an important issue. Plasma physics experiments require high density heavy ion beam and short pulsed bunch, which can be produced by non adiabatic compression of bunch implemented by a fast compression with 90° rotation in the longitudinal phase space. The phase space rotation in fast compression is initiated by a fast jump of the RF voltage amplitude. For this purpose, the CSR longitudinal bunch compression cavity, loaded with FINEMET FT 1M is studied and simulated with MAFIA code. In this paper, the CSR longitudinal bunch compression cavity is simulated and the initial bunch length of 238U72+ with 250 MeV/u will be compressed from 200 ns to 50 ns. The construction and RF properties of the CSR longitudinal bunch compression cavity are simulated and calculated also with MAFIA code. The operation frequency of the cavity is 1.15 MHz with peak voltage of 80kV, and the cavity can be used to compress heavy ions in the CSR.     

用于质子加速器的壁电流探头的研制

针对中国散裂中子源快同步环上束团纵向长度和束流强度的测量工作以及973束流损失控制实验课题中束团时间结构的测量工作,研制了用于上述两台质子加速器的壁电流探头。介绍了使探头达到足够的带宽所做的改进工作。用高频电磁场仿真软件对探头的性能进行了模拟,验证了适用于壁电流探头的一些理论模型和加入屏蔽腔对探头高频响应曲线产生的影响以及做出相应的改进后所带来的效果。对实物探头的性能进行了测量实验,发现测量系统自身的不匹配对实验结果产生了影响,改进匹配后得到探头的幅频响应曲线在300 kHz~2 GHz的频率范围内基本保持一致。时域上对500 ns脉冲矩形波的测量结果也显示出探头良好的低频响应。     

Longitudinal RF capture and acceleration simulation in CSNS RCS

China Spallation Neutron Source (CSNS) is a high power proton accelerator-based facility. Uncontrolled beam loss is a major concern in designing the CSNS to control the radioactivation level. For the Rapid Cycling Synchrotron (RCS) of the CSNS, the repetition frequency is too high for the longitudinal motion to be fully adiabatic. Significant beam loss happens during the RF capture and initial acceleration of the injection period. To reduce the longitudinal beam loss, beam chopping and momentum offset painting methods are used in the RCS injection. This paper presents detailed studies on the longitudinal motion in the RCS by using the ORBIT simulations, which include different beam chopping factors, momentum offsets and RF voltage optimization. With a trade-off between the longitudinal beam loss and transverse incoherent tune shift that will also result in beam losses, optimized longitudinal painting schemes are obtained.     

Digital methods for diagnostics of longitudinal bunch parameters in synchrotrons

Methods are discussed for processing a digital signal (proportional to a longitudinal intensity of bunches during their acceleration in the synchrotron) in order to identify the time dependences of (i) a bunch phase relative to a phase of accelerating voltage, (ii) the rms longitudinal dimension of a bunch, and (iii) the intensities of a bunch and a beam (as a batch of circulating bunches). Examples of the dependences obtained for a beam in the nuclotron at the Joint Institute for Nuclear Research are presented.     

Bunch compression study using the envelope model in CSRm

The feasibility of attaining a short-pulse-duration heavy ion beam with a nanosecond pulse length is studied in the main ring of the Heavy Ion Research Facility in Lanzhou (HIRFL). Such a heavy ion beam can be produced by non-adiabatic compression, and it is implemented by fast rotation in the longitudinal phase space. In this paper, the possible beam parameters during longitudinal bunch compression are studied by using the envelope model. The result shows that a shortest heavy ion bunch ²³⁸U²⁸⁺ of 29 ns with energy of 200 MeV/u can be obtained, which can satisfy high energy density physics research.     

Longitudinal Single Bunch Instability Caused by Wake Field of Electron Cloud

The electron cloud accumulated in the vicinity of positron beam generates longitudinal electric field during the passage of bunch. The longitudinal interaction between bunch and electron cloud can lead to the distortion of the bunch shape. We use a simple analytic formula to calculate the longitudinal electric field due to electron cloud. Based on the longitudinal wake field, the macro-particle tracking method is used to simulate the variation of bunch longitudinal profile in different electron cloud densities and the simulation also shows that the synchrotron oscillation tune is slightly shifted by the wake field. By comparing the simulation results and the analytical estimation from potential distortion theory, the longitudinal wake field from electron cloud can be seen as a potential well effect.     

Theoretical study of a dual harmonic system and its application to the CSNS/RCS

Dual harmonic systems have been widely used in high intensity proton synchrotrons to suppress the space charge effect,as well as reduce the beam loss.To investigate the longitudinal beam dynamics in a dual rf system,the potential well,the sub-buckets in the bunch and the multi-solutions of the phase equation are studied theoretically in this paper.Based on these theoretical studies,optimization of bunching factor and rf voltage waveform are made for the dual harmonic rf system in the upgrade phase of the China Spallation Neutron Source Rapid Cycling Synchrotron(CSNS/RCS).In the optimization process,the simulation with space charge effect is done using a newly developed code,C-SCSIM.     

HIAF-BRing束团合并过程中的束流负载效应模拟

强流重离子加速器HIAF-BRing在加速完成后进行束团合并，为研究BRing中的束流负载效应对束团合并的影响，对238U35+束流进行了粒子跟踪模拟。模拟结果显示，在束团合并过程中，束流负载效应引起束团长度和束团中心位置的振荡，导致束流动量分散和束团长度的增长。束团合并过程中尾场电压以及不同束团间尾场的耦合导致的势阱畸变，是引起束团长度和束团中心振荡及束流发射度增长的原因。为了降低束流负载效应的影响，采用多谐波前馈系统进行补偿，达到了补偿束团合并过程中的束流负载效应的目的，从而确保了BRing中引出束流的品质，同时根据模拟结果确定了前馈系统需要覆盖的频率范围和需要补偿的最大尾场电压。     

Laser wakefield acceleration of short electron bunches

The theory of electron acceleration in a plasma wake wave is developed, and the dependence of the main characteristics of accelerated electron bunches on the wakefield parameters is investigated, It is shown that using a prebunching stage, under proper conditions, the final electron density of a compressed and accelerated bunch can exceed the initial electron beam density by orders of magnitude and that longitudinal bunch compression provides quasi-monoenergetic acceleration to high energies, It is demonstrated that, for an initial electron beam radius smaller than the optimal one for efficient beam trapping, the energy spread of the compressed and accelerated electron bunch and its length can be evaluated by using the simple analytical predictions of a one-dimensional (1-D) theory. The obtained analytical results are confirmed by three-dimensional (3-D) numerical modeling     

合肥光源逐束团测量和横向束流反馈系统设计

 介绍了在合肥光源开展逐束团测量（横向和纵向）和横向束流反馈系统研究和研制的重要性,同时还介绍了设计思想。合肥光源高频频率为204 MHz，因此，系统至少需要100 MHz的带宽。还较详细地介绍了宽带部件和系统参数的选择原则。该系统不仅可用于研究由于高频腔中的高阶模和真空室的阻抗壁效应所引起的耦合束团不稳定性，而且还能抑制耦合束团不稳定性振荡、快速束流离子不稳定性和注入大幅度振荡等，从而将提高机器的运行性能。