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.     

快循环同步加速器射频加速电压幅度的数字化控制

 中国散裂中子源(CSNS)快循环同步加速器（RCS）中的射频低电平控制系统是基于FPGA的全数字控制系统,旨在完成对射频频率、加速电压和同步加速相位的控制。介绍了CSNS/RCS射频系统的低电平数字化控制设计方案,并着重对射频加速电压幅度控制回路进行了分析与讨论。电压幅度控制环路通过射频电压幅度信号与电压幅度设定值的比较,得到误差信号。误差信号经过控制器来控制输入到射频腔的功率,以达到稳定和改变腔压的目的。通过对控制对象的分析和建模,得到了满足系统要求的控制器。详细介绍了数字系统的实现,尤其是信号的解调和控制算法的实现。用ALTERA公司的DSP builder进行数字控制系统开发,系统仿真结果表明,环路误差信号大约于10 μs（400个系统时钟）后归于0,整个电压幅度控制环路能稳定运行。     

中国散裂中子源直线加速器束流流强测量系统

介绍了中国散裂中子源(CSNS)直线加速器(Linac)采用的自主研制的束流变压器(BCT)系统。根据CSNS Linac的束流参数、加速器管道的横向孔径和纵向空间,专门设计了BCT进行束流宏脉冲流强的测量。在CSNS Linac试运行阶段成功地测量到了负氢粒子束流的宏脉冲信息,给调束运行提供了有利的保障和支撑。     

Study on space charge effects of the CSNS/RCS

The Rapid Cycling Synchrotron (RCS) is a key component of the China Spallation Neutron Source (CSNS). The space charge effect is one of the most important issues in the CSNS/RCS, which limits the maximum beam intensity, as well as the maximum beam power. Space charge effects are the main source of emittance growth and beam loss in the RCS. Space charge effects have been studied by simulation for the CSNS/RCS. By optimizing the painting orbit, the optimized painting distribution was obtained. The space charge effects during the acceleration are studied and dangerous resonances, which may induce emittance growth and beam loss, are investigated. The results are an important reference for the design and commissioning of the CSNS/RCS.     

Introduction to the overall physics design of CSNS accelerators

The China Spallation Neutron Source (CSNS) is an accelerator-based facility. The     

Simulation on buildup of electron cloud in a proton circular accelerator

Electron cloud interaction with high energy positive beams are believed responsible for various undesirable effects such as vacuum degradation, collective beam instability and even beam loss in high power proton circular accelerators. An important uncertainty in predicting electron cloud instability lies in the detailed processes of the generation and accumulation of the electron cloud. The simulation on the build-up of electron cloud is necessary to further studies on beam instability caused by electron clouds. The China Spallation Neutron Source(CSNS) is an intense proton accelerator facility now being built, whose accelerator complex includes two main parts: an H-linac and a rapid cycling synchrotron(RCS). The RCS accumulates the 80 Me V proton beam and accelerates it to 1.6 Ge V with a repetition rate of 25 Hz. During beam injection with lower energy, the emerging electron cloud may cause serious instability and beam loss on the vacuum pipe. A simulation code has been developed to simulate the build-up,distribution and density of electron cloud in CSNS/RCS.     

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.     

Introduction to the overall physics design of CSNS accelerators

The China Spallation Neutron Source (CSNS) is an accelerator-based facility. The accelerator of CSNS consists of a low energy linac, a Rapid Cycling Synchrotron (RCS) and two beam transport lines. The overall physics design of CSNS accelerator is described, including the design principle, the choice of the main parameters and design of each part of accelerators. The key problems of the physics design, such as beam loss and control, are also discussed. The interface between the different parts of accelerator, as well as between accelerator and target, are introduced.     

散裂靶中质子束窗的散射效应

 质子束窗是在高功率靶区中的一个分界窗,它将质子输运线上高真空区域和氦容器中的氦环境分开。在其他散裂中子源中质子束窗的热效应以及机械问题都已经被研究过了,但质子束在该窗中散射效应的研究却很少被报导,然而在靶设计中如果没有处理好质子束窗的散射效应会有很大的问题。报导了质子束窗散射效应的模拟计算结果,包括不同质子束窗的材料和结构选择,并以中国散裂中子源（CSNS）为例,介绍了在CSNS一期和二期中质子束窗采用周边水冷的铝合金单层结构,CSNS三期采用中间水冷的铝合金夹层结构。文中给出了不同结构的质子束窗和不同的与靶距离散射效应对靶上经非线性磁铁均匀化的束流分布的影响的模拟计算结果。模拟结果显示质子窗的散射效应对束流损失和靶上的束流分布有重要的影响。     

中国散裂中子源快循环同步加速器中色品校正及六极磁铁非线性效应

中国散裂中子源（CSNS）快循环同步加速器（RCS）把能量为80 MeV的束流储存并加速到1.6 GeV然后引出到靶站。为了减少RCS中的束流损失，有必要对RCS做色品校正，并减小动量偏移对束流光学的影响。尝试了多种色品校正方案并对不同色品校正方案做了比较。用三维跟踪程序SIMPSONS研究了色品校正六极铁与空间电荷效应对束流的影响。色品校正六极铁可以有效减小色品引起的频散，但是由于六极铁为非线性元件，导致不同振幅的粒子间有一定频散。模拟发现同时存在空间电荷效应和色品校正六极铁时，会有少量的束流损失。     

CSNS反角白光中子源束线控制系统研制

中国散裂中子源(CSNS)反角白光中子源束线主要由中子束窗、中子开关、中子准直器和真空管道等组成。为了保证CSNS反角白光中子源束线安全、稳定、可靠地运行,研制了基于EPICS(Experimental Physics and Industrial Control System)软件架构的控制系统。该系统主要由中子束窗、中子开关及中子准直器的运动控制系统、真空控制系统和控制室三部分组成,实现了对反角白光中子源束线主要设备的远程监测和控制。测试结果表明,该系统具有稳定可靠性高、人机交互友好的特点,很好地满足了反角白光中子源束线运行的需要。     

Beam-loss driven injection optimization for CSNS/RCS

This paper summarizes the painting injection optimization for the Chinese Spallation Neutron Source （CSNS） ring. This optimization focuses on two main design goals： the lower beam loss and a spacecharge tune shift low enough to avoid strong resonances. Finally, the 3-D particle tracking is performed and we get some important results about the beam properties and beam loss.     

Beam-loss driven injection optimization for CSNS/RCS

This paper summarizes the painting injection optimization for the Chinese Spallation Neutron Source (CSNS) ring. This optimization focuses on two main design goals: the lower beam loss and a space-charge tune shift low enough to avoid strong resonances. Finally, the 3-D particle tracking is performed and we get some important results about the beam properties and beam loss.     

CSNS束流损失测量系统设计

介绍了束流损失测量系统探测器的选型、前置放大电子学的功能、数据采集系统的硬件配置及本地站显示界面,着重介绍了本系统在加速器不同能量段的束流调试中的应用。DTL低能段成功观测到了束流损失,针对RCS段脉冲高功率设备,对本系统的干扰提出了解决方案,便于加速器调束时区分干扰与束损,针对RTBT微脉冲大信号的束损进行了积分展宽,满足数据采集系统带宽需求。     

Emittance coupling driven by space charge in the CSNS linac

In the conventional design of RF linacs, the bunched beams are not in thermal equilibrium. The space charge forces couple the particle motions between the transverse and the longitudinal directions. Fur-thermore it will cause the equipartitioning process which leads to emittance growth and halo formation. In the design of the China Spallation Neutron Source (CSNS) linac, three cases are investigated using the Hofmann stability charts. In this paper, we present the equipartitioning beam study of the CSNS Alvarez DTL linac.     

Emittance coupling driven by space charge in the CSNS linac

In the conventional design of RF linacs, the bunched beams are not in thermal equilibrium. The space charge forces couple the particle motions between the transverse and the longitudinal directions. Furthermore it will cause the equipartitioning process which leads to emittance growth and halo formation. In the design of the China Spallation Neutron Source （CSNS） linac, three cases are investigated using the Hofmann stability charts. In this paper, we present the equipartitioning beam study of the CSNS Alvarez DTL linac.     

Study of the design of CSNS MEBT

The design of CSNS MEBT has two objectives：（1） to match the beam both in the transversal direction and the longitudinal direction from RFQ into DTL;（2） to further chop the beam into the required time structure asked by RCS. It is very diffcult and critical to control well the emittance growth and in the meantime to match and chop the beam. Firstly,the optical design is done and optimized,and the multi-particle simulations show that the maximum emittance growth is successfully controlled within 14%. Secondly,based on the different beam envelopes obtained by TRACE-3D and PARMELA,the least deflecting angle of the chopper is determined by TRACE-3D. At last,the field of steering magnet is determined through simulations.     

环-靶站输运线末端准直器的研究

环-靶站输运线(RTBT)末端的准直器是中国散裂中子源(CSNS)工程中的关键部件之一,因其靠近靶站,辐射剂量大,维护困难,故设计可靠性极为重要。根据准直器的工作原理,及CSNS物理设计要求,对比国外同类加速器的设计经验,设计完成准直器设备。在设计过程中兼顾了热沉积、功率损耗和材料性能等方面的严格要求,并逐一阐述了具体方案。利用Bethe-Bloch公式计算与SRIM软件模拟的结果比较,确定了模拟工具和模拟方法的可靠性,根据ANSYS有限元软件模拟的结果,验证了准直器结构设计的可靠性。     

中国散裂中子源快循环同步加速器壁电流探测系统

在中国散裂中子源工程中, 快循环同步加速器负责将剥离注入的能量为80MeV的质子束加速至1.6GeV后引出。在快循环同步加速器上共安装了两台壁电流探测器, 用来观测束流从注入至引出过程中束团在时域上的变化情况。详细介绍了壁电流探测器在陶瓷间隙、磁性材料和匹配电阻等方面的设计考虑, 以达到带宽满足百kHz到30 MHz的设计目标, 并对实际带束流测量结果进行分析讨论。经实际在线运行测试, 此壁电流探测器完全满足束流调试及运行需要。     

强流质子加速器ns级快沿切束电源系统

详细分析了中国散裂中子源(CSNS)直线加速器低能端预切束电源工作原理。切束束团上升沿和下降沿的快慢是衡量切束电源性能好坏的重要指标,经过研究,研制了一台脉冲幅值6 kV,前后沿纳秒级的切束腔电源,应用纯硬件电路代替软件的方法实现高频和低频定时信号的同步和与处理,使该电源输出稳定可靠的高压脉冲。该电源基于直流高压加快速高压开关的设计方案来实现高压、高重复频率及纳秒级快沿的脉冲输出,具有多脉冲和单脉冲两种工作模式,满足了直线加速器单束团和多束团注入到快循环质子同步加速器(RCS)的要求。CSNS直线加速器切束实验的结果表明,切束电源满足各项设计指标要求。