Development of readout electronics for bunch arrival-time monitor system at SXFEL

A bunch arrival-time monitor(BAM) system,based on electro-optical intensity modulation scheme, is under study at Shanghai Soft X-ray Free Electron Laser.The aim of the study is to achieve high-precision time measurement for minimizing bunch fluctuations. A readout electronics is developed to fulfill the requirements of the BAM system. The readout electronics is mainly composed of a signal conditioning circuit, field-programmable gate array(FPGA), mezzanine card(FMC150), and powerful FPGA carrier board. The signal conditioning circuit converts the laser pulses into electrical pulse signals using a photodiode. Thereafter, it performs splitting and low-noise amplification to achieve the best voltage sampling performance of the dual-channel analog-to-digital converter(ADC) in FMC150. The FMC150 ADC daughter card includes a 14-bit 250 Msps dual-channel high-speed ADC,a clock configuration, and a management module. The powerful FPGA carrier board is a commercial high-performance Xilinx Kintex-7 FPGA evaluation board. To achieve clock and data alignment for ADC data capture at a high sampling rate, we used ISERDES, IDELAY, and dedicated carry-in resources in the Kintex-7 FPGA. This paper presents a detailed development of the readout electronics in the BAM system and its performance.     

X-band deflecting cavity design for ultra-short bunch length measurement of SXFEL at SINAP

For developing the X-ray Free Electron Lasers test facility(SXFEL) at Shanghai Institute of Applied Physics,Chinese Academy of Sciences(SINAP), ultra-short bunch is the crucial requirement for excellent lasing performance. It is a big challenge for deflecting cavity to measure the length of ultra-short bunch, and higher deflecting gradient is required for higher measurement resolution. X-band travelling wave deflecting structure has features of higher deflecting voltage and compact structure, which has good performance at ultra-short bunch length measurement. In this paper, a new X-band deflecting structure is designed to operate in HEM11-2π/3 mode.For suppressing the polarization of deflecting plane of the HEM11 mode, two symmetrical caves are added on the cavity wall to separate two polarized modes.     

Sub-picosecond electron bunch length measurement using coherent transition radiation at SXFEL

Longitudinal electron bunch length plays a significant role in single-pass free-electron lasers(FEL), as the high-gain FEL process depends strongly on the high peak current of electron bunches. Longitudinal electron bunch length was measured by detecting the interferogram of coherent transition radiation generated by electron bunches using a THz interferometer and a Golay cell(spectral range0.02-20 THz) at Shanghai X-ray free-electron laser. The detailed process of measurement and data analysis are discussed herein. Furthermore, the electron bunch length was estimated based on the dispersive strength R_(56) of the bunch compressor and the energy spread δ of electron bunches, which were obtained via experiments. The comparison showed that the measured bunch length was consistent with the estimated bunch length.     

SDUV-FEL装置上利用电光频谱解码法测量束团长度实验设计与仿真

电子束团纵向长度是束流诊断中的重要参数,电光频谱解码法(Electro-Optical Spectral Decoding,EOSD)是为数不多的可进行单发测量的高时间分辨率测量方法。本文基于上海深紫外自由电子激光装置(Shanghai Deep Ultraviolet Free Electron Laser,SDUV-FEL)设计了一套电光频谱解码法测量束团长度实验方案。通过采用针尖粗同步和可调的光栅展宽器可实现长度在1-10 ps内变化的束团无损测量。通过对电光调制过程及其后探测的仿真研究表明,选用0.5 mm厚的Zn Te晶体在距离束流中心3-5 mm处测量时,时间分辨率最高可达180 fs(Root Mean Square,RMS),信号展宽在3%以内,测量的电场形状无可观测畸变,满足SDUV-FEL的实验需求。     

Analysis and optimization of high-power pulse transformer for SXFEL

Longitudinal injection is a promising on-axis injection scheme for diffraction-limited storage rings. In the latest version of the Hefei advanced light source(HALS), both the dynamic aperture and momentum aperture have been optimized. A longitudinal injection scheme was investigated on the HALS using a doublefrequency radio frequency system. To evaluate the injection performance, various errors were considered. A series of tracking simulations were conducted, and the injection efficiency was obtained under different error levels.     

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.     

Beam test results of high Q CBPM prototype for SXFEL

In pursuit of high-precision beam position measurements at micrometers or submicrometers for the Shanghai soft X-ray free-electron laser (SXFEL) facility which is under construction in the vicinity of the Shanghai Synchrotron Radiation Facility,a high Q cavity beam position monitor (CBPM) with a resonant frequency of 4.7 GHz is developed by the Shanghai Institute of Applied Physics,and the relevant BPM electronics with a dedicated RF front end,and a digital BPM,are completed.The cavity design,cold test,system architecture,and first beam test are performed at the Shanghai deep ultraviolet free-electron laser (Zhao et al.in Nucl Instrum Meth A 528(1-2):591-594,2004.doi:10.1016/j.nima.2004.04.108) facility.Results of the beam experiment show that the performance of the CBPM is consistent with basic expectations,and the beam position resolution can fulfill the requirements for the SXFEL project if the beam conditions are optimized.     

Design and study of a C-band pulse compressor for the SXFEL linac

A C-band RF pulse compressor is in development at SINAP It comprises of two resonant cavities,two mode convertors and a 3 dB power divider.TE_(0.1.15)mode is selected for obtaining higher quality factor Q_0 of the RF pulse compressor cavities,so that the power gain factor can be 3.2,which is supposed to multiply the RF power from 50 MW to 1 60 MW.In this paper,we report our work on C-band RF pulse compressor,namely the design simulation and cold test results.     

Design study of neutron flux intensity monitor between ten and several hundred keV for BNCT

Based on the activation method using ⁷¹Ga(n,γ)⁷²Ga reaction, two spherical monitors with gallium nitride (GaN) wafers as activation material were designed by Monte Carlo simulations to precisely measure the absolute integral neutron flux intensity between ten and several hundred keV. The two monitors are almost the same in shape and have an absorber/moderator/absorber/GaN arrangement from outside to inside. The differences between the two monitors are the kind of materials, the thicknesses of the absorbers and the diameter of the moderator. By making difference of the sensitivities between these two monitors, the contributions of thermal, epithermal and very high energy fast neutrons were removed completely, and constant monitor sensitivity to neutrons between ten and several hundred keV was extracted. The simulation results and related analysis indicated that the absolute integral neutron flux intensity between ten and several hundred keV could be precisely measured by the presently designed two monitors.     

Compact lithium-glass neutron beam monitor for SANS at CSNS

A small-angle scattering neutron spectrometer for material research is under construction at the China Spallation Neutron Source. An intervening neutron beam monitor behind the sample is needed to measure the beam intensity in order to reduce the measurement uncertainty caused by beam fluctuation. Considering the mobility requirement and limited space, we proposed a compact monitor using a type of lithium-glass scintillator provided by China Building Materials Academy. Its performance was studied experimentally using ~(252)Cf and ~(60)Co sources.The neutron light yield of the selected scintillator was measured to be 5:3 × 10~3 photons/neutron. The feasibility of n-gamma discrimination using the charge comparison method was verified. By using the Geant4 toolkit, themonitor was modeled with precise physical processes including neutron tracking, scintillation, and optical photon transmission. The gamma sensitivity and detection efficiency were investigated in the simulation. It was concluded that a 0.5-mm-thick lithium-glass scintillator with natural lithium is an appropriate choice to satisfy both the neutron detection efficiency and gamma elimination requirements.     

Design of an epi-thermal neutron flux intensity monitor with GaN wafer for boron neutron capture therapy

Boron neutron capture therapy (BNCT) is a promising cancer therapy. Epi-thermal neutron (0.5 eV < E_n < 10 keV) flux intensity is one of the basic characteristics for modern BNCT. In this work, based on the ⁷¹Ga(n,γ)⁷²Ga reaction, a new simple monitor with gallium nitride (GaN) wafer as activation material was designed by Monte Carlo simulations to precisely measure the absolute integral flux intensity of epi-thermal neutrons especially for practical BNCT. In the monitor, a GaN wafer was positioned in the center of a polyethylene sphere as neutron moderator covered with cadmium (Cd) layer as thermal neutron absorber outside. The simulation results and related analysis indicated that the epi-thermal neutron flux intensity could be precisely measured by the presently designed monitor.     

电子直线加速器束团长度监测器研究

对电子直线加速器束团长度监测器进行了综述.介绍了各种束团长度的测量原理和优缺点.并结合试验结果,指出了其中一些监测器在实际设计使用过程应当注意的问题.其中的许多监测器测量时无需截断束流,能够实时测量,测量精度高.     

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。     

脉冲调制器机柜屏蔽效能分析测试

高功率脉冲调制器是电子直线加速器(LINAC)的功率源,脉冲调制器在运行中会产生很强的电磁干扰.为了满足上海光源LINAC的高精度要求,脉冲调制器必须尽量抑制这些电磁干扰.本文介绍对上海光源150MeV高性能LINAC调制器的电磁辐射抑制的分析研究和测试.分析了电磁辐射的泄漏途径,对调制器机柜的屏蔽效能进行了定性、定量分析,并进行了测试.验证了调制器机柜的EMC设计制作对电磁干扰抑制的有效性.     

HLS单束团时序系统的参数测试及在线实验

为实现合肥同步辐射光源（ＨＬＳ）单束团注入,研制出一套单束团时序系统＾「１、２」。其主要特点是系统输出各时序信号与贮存环高频信号保持同步以及时序信号时间抖动小。实验结果显示,快速通道时序信号的时间抖动小于２００ｐｓ。该系统在线实验获得成功。     

Improvement on a Michelson interferometer for bunch length measurement of a femtosecond accelerator

Based on the femtosecond accelerator facility at Shanghai Institute of Applied Physics (SINAP),a conventional far-infrared Michelson interferometer was built to measure the bunch length by means of optical autocorrelation.However,according to the preliminary experiment result,the resolution of interferometer is not good enough,because the mirror-driving mechanism makes the moving mirror tend to tilt or wobble as it retards.Considering of the allowable errors,we calculate the maximum allowable titling angle of the moving mirror,and discuss the alignment plan in this paper.     

北京大学EN型串列静电加速器的控制及监测

叙述了北京大学EN型串列静电加速器的高压充电及稳定系统,介绍了用光纤技术实现负离子源工作参量的遥测以及用程控机实现真空系统控制自动化。     

Exploration of a MgO cathode for improving the intensity of pulsed discharge plasma at atmosphere

With regard to the lower density and energy of electrons in pulsed discharge plasma (PDP) at atmosphere, leading to the lower energy utilization of plasma, we propose a MgO cathode to enhance the plasma intensity according to field emission principle. The MgO cathode is prepared by an electro-depositing MgO film on a stainless steel plate. This way, the positive charges come to the cathode and accumulate on the surface of the MgO film, leading to the enhancement of the electric field intensity between the cathode and MgO film, and result in the strong emission of secondary electrons from the MgO cathode. As a result, the intensity of plasma can be enhanced. Herein, the effect of the MgO cathode on the intensity of PDP is investigated. It was shown that the discharge peak current was improved by 20% compared with that of without the MgO cathode. With increasing the MgO film thickness, discharge intensity, including the peak current, transforming charge and spectrum intensity first increased and then decreased. Higher enhancement of peak current, transforming charge and spectrum intensity were acquired with a higher peak voltage. Compared to a cathode without MgO film, the ozone production is higher with MgO cathode employed. The research proposes a novel approach for improving the intensity of discharge plasma, and also provides a reference for further application of PDP.     

实时风险监测系统在田湾核电站的研发与应用

风险监测系统是概率安全分析最重要的应用工具之一,在全球各核电站风险决策领域中得到了广泛应用。本文详细介绍了田湾核电站风险监测模型的研发与管理,系统网络架构与多用户应用、实时监测研发与应用、计划自动导入和计算时效性提升等重要特征,以及在电站的针对性应用方案研究,最后讨论了风险监测系统存在的问题与挑战。     

Development of a high intensity Al beam from SiC targets for accelerated beam experiments at ISAC

An intense beam of ^26gAl has been developed for accelerated beam experiments at TRIUMF’s ISAC facility. Studies of the on-line production of Al radionuclides from thick silicon carbide targets have been performed as part of a program of beam development for astrophysical reaction studies at ISAC. While the release of short-lived Al nuclides from SiC was found to be slow, development of new target material forms and high-power target containers has allowed operation of SiC targets with proton currents of up to 70 μA on target. In addition, operation with the TRIUMF resonant ionization laser ion source (TRILIS) has produced ^26gAl beam intensities of 5.1 × 10¹⁰ s⁻¹.