Study of the crosstalk evaluation for cavity BPM

In order to pursue high-precision beam position measurements for free-electron laser facilities, a cavity beam position monitor(CBPM) is employed to measure the transverse position that can meet the requirement of position resolution at a sub-micrometer or even nanometer scale. However, for the pill-box cavity BPM, crosstalk between the cavities will have an effect on the accurate measurement of beam position. To reduce the effect of crosstalk on CBPM performance and ease the measurement of the isolation between the cavities, the cavities with a slight difference in resonant frequency were designed and applied in the Dalian coherent light source and Shanghai soft X-ray free-electron laser facilities. Furthermore, two methods, the principal component analysis method and the method of harmonic analysis, are proposed in this paper to evaluate the crosstalk. The results demonstrate that the two methods are feasible in evaluating the crosstalk between the cavities.     

SHINE腔式BPM系统射频信号调理前端研制

基于低温超导直线加速器的上海硬X射线自由电子激光装置（SHINE）需1个分辨率可达200 nm的束流位置测量系统,以实现电子束与光子束在波荡器中的紧密相互作用和能量交换。现已研制的束流位置测量系统不能完全满足上述要求,为此,基于对关键技术指标的分配,设计研制了一个由C波段腔式探头、低噪声系数的单路下变频至低中频的射频信号调理前端以及专用数字信号束流位置处理器构成的CBPM系统样机。而作为连接腔式探头和数字信号采集电子学之间的桥梁,射频信号调理前端（radio frequency front end, RF前端）的结构和性能也直接决定了CBPM系统的性能。本文从SHINE对CBPM系统的整体需求为出发点,分析了系统对射频信号调理前端的指标分配,提出了一种放大器开关切换型RF前端的方案设计,并成功搭建了1套可模拟束流条件的离线全锁相采样测试平台。此外,在上海软X射线自由电子激光装置（SXFEL）中搭建了测试平台并完成了射频信号调理前端的带束性能评估,束流实验结果表明,在束团电荷量为100 pC、系统动态范围在±100 μm的条件下,采用腔式探头射频信号一分二的评估方法,位置分辨率可达71 nm,优于设计指标需求。     

上海光源数字化束流位置信号处理器测试平台研制

数字化束流位置信号处理器(Digital Beam Position Monitor Processor,DBPM)是上海光源自主研发作为束流位置监测(Beam Position Monitor,BPM)的主要设备。针对DBPM电子学处理器产品化测试需求开发了一套基于MATLAB和程控技术的自动化测试平台,用于处理器批量测试验收和性能评估。平台使用Agilent MXG信号源和一分四功分器模拟4路真实探头信号,经过处理器采集处理后被上位机接收。测试仪器的设置和实验数据的获取,整个系统是基于客户端和服务器架构实现的。采用物理实验与工业控制系统(Experimental Physics and Industrial Control System,EPICS)的通道访问Lab CA接口实现数据的实时采集。目前该测试平台已经成功应用于大连自由电子激光装置和上海软X射线自由电子激光装置的DBPM处理器验收测试,处理器幅频响应曲线,不同衰减下模数变换器(Analog to Digital Converter,ADC)噪声水平测试、衰减步长一致性、通道间串扰及信噪比测试结果均达到设计指标。     

Cavity Beam Position Monitor System for Shanghai Soft X-ray Free Electron Laser

Shanghai Soft X-ray Free Electron Laser (SXFEL) requires a beam position monitor system with resolution of sub-micron, so the beam based alignment (BBA) method to achieve close coincidence of the electron beam and the photon beam in the undulator section can be used. A cavity beam position monitor (CBPM) system consisting of a C-band cavity probe, a RF front-end and a dedicated digital beam position monitor processor (DBPM) was developed. The system design, hardware and software structure, and system construction were introduced in this paper. Based on the three adjacent CBPM systems in the drift section, the online system performance evaluation was completed. And the experiment results show that the position resolution of 880 nm is obtained under the condition of the bunch charge of 500 pC and the dynamic range of the system of ±800 μm. This is also the first CBPM system with submicron position resolution that can be run online in China. In addition, the phase cavity of CBPM was used to measure the relative charge and the arrival time of the bunch. The evaluation results show that the performance is better than the design requirements of SXFEL.     

上海软X射线自由电子激光腔式束流位置测量系统

上海软X射线自由电子激光装置（Shanghai Soft X-ray Free Electron Laser, SXFEL）需1个分辨率达到亚μm量级的束流位置测量系统,并采用基于束流准直的方法实现波荡器段电子束与光子束的紧密重合。为此设计研制了1个由C波段腔式探头、单路混频至低中频的射频前端以及自主研发的专用数字信号束流位置处理器（digital beam position monitor processor, DBPM）构成的腔式束流位置测量（cavity beam position monitor, CBPM）系统。本文对系统的设计、软硬件结构、系统搭建进行了介绍,并基于漂移段搭建的3个紧邻的CBPM阵列完成了在线系统性能评估。束流实验结果表明,在束团电荷量为500 pC、系统动态范围在±800 μm的条件下,位置分辨率可达880 nm,这也是国内首次研制成功可在线运行的具有亚μm位置分辨率的CBPM系统。此外,采用CBPM的相位腔进行相对束团电荷量、束团到达时间的测量,其性能评估结果也均优于SXFEL设计要求。     

Wakefields studies for the SXFEL user facility

Besides the original seeded undulator line,in the soft X-ray free-electron laser (SXFEL) user facility in Shanghai,a second undulator line based on self-amplified spontaneous emission is proposed to achieve 2-nm laser pulse with extremely high brightness.In this paper,the beam energy deviation induced by the undulator wakefields is numerically calculated,and 3D and 2D results agree well with each other.The beam energy loss along the undulator degrades the expected FEL output performances,i.e.,the pulse energy,radiation power and spectrum,which can be compensated with a proper taper in the undulator.Using the planned time-resolved diagnostic,a novel experiment is proposed to measure the SXFEL longitudinal wakefields.     

An on-line data acquisition system of oscilloscope-embedded input/output controller for cavity BPM measurement

Cavity beam position monitor(BPM) is widely used in a precise electron beam position measurement. Based on high performance oscilloscope-embedded EPICS input/output controller,we developed an on-line cavity BPM signal processing system for fast data acquisition solution when designing a cavity BPM.Also,methods for extracting the position information from cavity pickup signals and calibration algorithm are included in this solution.     

腔式束流位置探测器的设计与实验研究

束流位置探测器对自由电子激光装置的研制和运行具有重要的意义。其中,腔式束流位置探测器(腔式BPM)又以其高精度、高分辨率的特点而得到广泛的应用。本文对应用于上海深紫外自由电子激光装置上的腔式BPM进行了理论分析、模拟计算和BPM腔的测量等方面的研究。     

SXFEL装置上速调管输入输出特性曲线的线性化

在上海软X射线自由电子激光(Soft X-ray Free-electron Laser,SXFEL)中的微波低电平控制系统中,通过对各速调管的输出信号进行测量和控制,保证加速器的稳定运行并且达到技术指标。另一方面,SXFEL中的脉冲速调管的输入输出特性存在非线性的关系,这种电子管放大器不理想的非线性特性会导致微波低电平(Low Level Radio Frequency,LLRF)控制系统调节的效率降低。基于SXFEL装置,采用基于现场可编程门阵列(Field Programmable Gate Array,FPGA)的数字预失真方法,在LLRF控制系统中设计了一套实现高功率速调管放大器线性化的在线系统。S波段加速装置和其相应的东芝E3730A速调管及高压调制器和低电平系统实地测试结果表明,在LLRF控制系统中建立的在线系统能够有效补偿速调管带来的非线性问题,提高微波低电平控制系统的精度及准确性。     

基于软件无线电的新型数字束流位置处理器

研究了基于软件无线电架构的新型数字束流位置处理器,介绍了处理器样机的射频、模数转换和数字处理模块的硬件架构和主要参数。针对处理器多通道的不对称性,提出了校准方案。测试结果表明,处理器逐圈位置电子学分辨率在输入大于–30 dBm时,优于1.5μm;输入大于–27 dBm时,电子学分辨率达到亚微米量级。处理器在上海光源储存环流强为150 mA条件下测试,逐圈位置分辨率优于2μm,并能够准确获取包含束流实时信息的逐圈位置信号。     

Analysis and optimization of high-power pulse transformer for SXFEL

A C-band accelerator structure was used to accelerate electrons at the Shanghai soft X-ray free-electron laser test facility(SXFEL-TF) in Shanghai Institute of Applied Physics(SINAP). The microwave system of this accelerator structure used a 110 MW pulse modulator and a klystron(PV-5050) to provide the power supply. A pulse transformer is a crucial device in a modulator klystron system and plays significant roles in voltage level transformation, matching impedances, and polarity inversion.This study presents the optimization of a high-voltage pulse transformer. The design considerations of reducingflattop ringing and flattop droop, and shortening leading edge are provided. The model simulation, mechanical design, and the relevant experimental results are also presented.     

上海硬X射线自由电子激光装置调试用束流收集桶的设计

在建上海硬X射线自由电子激光装置(Shanghai high repetition rate XFEL and extreme light facility,SHINE)包含一台8 GeV的超导直线加速器,100 PW的激光系统,三条波荡线和10条实验线站。主加速器的第三磁压缩段(BC3段)有一调试用的束流收集桶,BC3段的调试电子流强为0.3μA、能量为7.7 GeV,束流功率为2.31 kW。本文从材料对7.7 GeV电子的能量吸收方面考虑,对束流收集桶的结构进行了确定。用ANSYS 17.0对束流收集桶的温度场进行了分析,结果证明在有表面空气自然对流换热的情况下,铝芯的最高温度为193.14℃,在束流收集桶坑道无外界换气的情况下,束流收集桶需要外围冷却水;用蒙特卡罗程序FLUKA对束流收集桶的活化进行了分析,保守假设束流收集桶连续注束2 000 h。结果证明要保证停机1 h后,束流收集桶周围30 cm处的剩余辐射剂量小于25μSv/h,束流收集桶外围需要55～85 cm的混凝土屏蔽体;结果显示束流收集桶的剩余辐射剂量在30 min内衰减的非常快,这是由于刚停机时束流收集桶内产生的...     

基于相干渡越辐射的束团长度测量研究

电子束团长度是束流诊断中的重要参数,基于相干渡越辐射(Coherent Transition Radiation,CTR)的测量方法是一种简单易行的高时间分辨率测量方法。本文调研并分析了不同电子束团长度测量方法的优缺点,选择基于CTR方法作为主要研究方向,主要针对上海深紫外自由电子激光实验装置(Shanghai Deep Ultra-Violet Free Electron Laser,SDUV-FEL)和X射线自由电子激光试验装置(Shanghai X-ray Free Electron Laser,SXFEL)进行了实验方案设计和模拟分析。结果表明,通过合理的参数选择和方案优化,用该方法可对飞秒至皮秒范围内的束团长度进行测量,时间分辨率能到达飞秒量级,满足SDUV-FEL的实验需求和SXFEL的工程需求。     

Strip line beam position monitor for HLS LINAC

1 Introduction Beam position monitors at HLS LINAC and transfer line will deliver the information about the transverse positions and phases of beam passing by. Typical requirement for position resolution is within 1mm within 1/3 of half aperture rb (rb of HLS LINAC is 25mm). The HLS LINAC BPMs will also serve as beam phase detectors, which require a tough broad-band frequency response and impedance match for the BPMs. Additionally, space available for the BPMs at the HLS LINAC…     

基于BEPC Ⅱ的数字束流位置探测器信号处理算法的FPGA实现

数字束流位置探测器(BPM)算法是数字BPM系统最核心的部分,其对束流位置测量的精度起决定作用。本文在完成数字BPM算法MATLAB模拟工作的基础上,将模拟优选出的数字BPM算法在自制的电子学硬件上进行FPGA实现。首先介绍了数字BPM算法的总体设计和实现方案;其次介绍了数字BPM算法各功能模块的设计原理及其在FPGA中的具体实现方法;最后在输入信号频率499.8 MHz、强度-10 dBm、BPM探头灵敏度系数23的条件下进行了实验室测试。实验结果显示：逐圈位置分辨达2.96 μm,快响应位置分辨达0.65 μm,闭轨位置分辨达0.33 μm,验证了本算法在束流位置测量中具有良好性能。     

Development of button-type pickup for SSRF ring

In building Shanghai Synchrotron Radiation Facility(SSRF), in order to reduce or eliminate the unnecessary sources of beam motion, the precise and stable beam position measurement system in the feedback system was required. In this study, we focused on theoretical analysis of the electrode of beam position monitor(BPM).Simulations, including analytic derivations of the propagation impedance and the distribution inductance, were performed. The BPM was designed based on the results and the acceptance measurements of the impedance and the inductance by using the time domain reflection(TDR) with a network analyzer. It has been proved in years of operations that the BPM system meets the requirement of the resolution of sub-micron.     

西安质子应用装置BPM设计及测试结果

西安质子应用装置(XiPAF)中能传输段设有6个束流位置探测器(BPM)用于测量束流位置及相位,要求位置和相位测量分辨率分别好于0.1 mm和1°,绝对位置测量准确度好于±0.5 mm。本文从理论上分析了纽扣型BPM位置测量分辨率与电极长度及电极张角的关系,并结合CST模拟得到最优值,设计分辨率达24.5 μm。离线测试结果表明,BPM样机的电极电容、灵敏度及电极间耦合度均与设计值相符。利用旋转法测量得到BPM样机水平和竖直方向电中心与机械中心的偏差分别为（0.04±0.05） mm和（-1.53±0.05） mm。样机安装在清华大学微型脉冲强子源（CPHS）高能传输段进行测试,测试结果表明,XiPAF BPM位置测量分辨率好于60 μm,相位测量分辨率好于0.74°,绝对位置测量准确度为±0.35 mm。该设计满足西安质子应用装置的要求。     

数字BPM电子学在束流位置测量中流强依赖性研究

在BPM测量系统中,流强依赖(BCD)是影响BPM测量精度和可靠性的一个重要因素,本文通过对BPM信号处理链路分析、BPM计算方法的研究,探索在BPM测量过程中产生流强依赖的主要原因;并利用Matlab模拟实验、实验室测试、实际束流测试,找到解决BPM测量流强依赖的方法。研究结果表明,BPM信号处理通道的非线性、ADC的直流偏置是产生BPM测量流强依赖的两个主要因素。本文经过对BPM射频信号处理电路改进,对BPM信号算理算法的优化工作,解决了自研数字BPM电子学的流强依赖性问题。     

Modified model for harmonic generation free electron laser

The longitudinal modulation to the electron beam by a coherent seed laser pulse is widely used for generating fully coherent, short wavelength radiation in various harmonic generation free electron laser (FEL)schemes. After introducing the density modulation, mierostruetures down to attosecond scale are produced over the distance of one seed laser wavelength. In order to take into account the mierostructures in the theoretical and numerical analysis, in the frame of undulator period averaged approach, a modified model for harmonic generation FEL is developed in this paper. With the modified model, three harmonic generation FEL examples are investigated by employing Shanghai soft X-ray FEL (SXFEL) parameters. In FEL schemes with ultra-high harmonic generation and ultra-short pulse, the modified model presents some interesting aspects which are helpful for understanding of radiation pulse evolution, bunching efficiency and noise propagation issues.     

一种波荡器段间四极铁远程精密调节机构的研制

自由电子激光(Free Electron Laser,FEL)装置是一种以相对论高品质电子束作为工作介质,在周期磁场中以受激发射方式放大电磁辐射的新型激光源。FEL装置中的四极铁中心相对于束流中心线的高精度就位与否将直接影响束流的品质,上海软X射线自由电子激光装置和大连极紫外相干光源装置的波荡器段间四极铁均采用基于束流准直方法(Beam based alignment,BBA),需要可远程精密调节四极铁位置的机构。BBA四极铁远程精密调节机构主要由可远程精密定位的电移机构和控制系统构成。电移机构采用精密滚珠丝杠驱动的滑块组合机构,可实现垂直于束流的水平和竖直高度方向的二维调节。本文简单描述了BBA四极铁远程精密调节机构的机械设计,对BBA四极铁远程精密调节机构的测试方法及结果进行了详细分析。该系统集成测试结果表明,机构运动过程中采用光栅尺进行反馈,其定位精度和重复性均达到了设计指标要求。