Simulation and Error Analysis of Electro-optic Sampling Measurement of Ultrashort Electron Beam Bunch Length

For the development of high energy physics,it is needed to improve the performance of the relativistic electron bunch.The measurement of the ultrashort relativistic electron pulse becomes one of the key technologies.The electro-optic sampling measurement of relativistic electron pulses is a promising method.This method is nondestructive, non-intrusive,and real-time monitoring.Distance and angles of the reference frames will cause system deviations.In this paper these system deviations are analyzed by simulation.It provides a reference for the experiment.

Electro-optical sampling non-synchronous delay scanning measurement of electron beam bunch length at BFEL

The Electro-optical sampling delay scanning technique can be used for electron beam bunch length measurement. A novel non-synchronous delay scanning technique based on the electro-optical sampling measurements is presented. Based on Beijing Free Electron Laser （BFEL）, the electron beam bunch length was measured with the electro-optical sampling technique for the first time in China. The result shows that the electron beam bunch length at BFEL is about 5.6±1.2 ps.

Determining beam transverse absolute position by triangulation of multi-electrode signal phase differences

Accurate measurement of the transverse position of a beam is crucial in particle accelerators because it plays a key role in determining the beam parameters.Existing methods for beam-position measurement rely on the detection of image currents induced on electrodes or narrow-band wake field induced by a beam passing through a cavity-type structure.However,these methods have limitations.The indirect measurement of multiple parameters is computationally complex,requiring external calibration to determine the system parameters in advance.Furthermore,the utilization of the beam signal information is incomplete.Hence,this study proposes a novel method for measuring the absolute electron beam transverse position.By utilizing the geometric relationship between the center position of the measured electron beam and multiple detection electrodes and by analyzing the differences in the arrival times of the beam signals detected by these electrodes,the absolute transverse position of the electron beam crossing the electrode plane can be calculated.This method features absolute position measurement,a position sensitivity coefficient independent of vacuum chamber apertures,and no requirement for a symmetrical detector electrode layout.The feasibility of this method is validated through numerical simulations and beam experiments.

Terahertz coherent transition radiation based on an ultrashort electron bunching beam

The experimental result of terahertz （THz） coherent transition radiation generated from an ultrashort electron bunching beam is reported. During this experiment, the window for THz transmission from ultrahigh vacuum to free air is tested. The compact measurement system which can simultaneously test the THz wave power and frequency is built and proofed. With the help of improved Martin-Puplett interferometer and Kramers-Krong transform, the longitudinal bunch length is measured. The results show that the peak power of THz radiation wave is more than 80 kW, and its radiation frequency is from 0.1 THz to 1.5 THz.

Bunch-by-bunch beam size measurement during injection at Shanghai Synchrotron Radiation Facility

Fast beam profile measurement is important in fast beam dynamic behavior investigations. A bunch-bybunch beam size measurement system, which is presently used to measure horizontal profile, has been developed at the Shanghai Synchrotron Radiation Facility(SSRF) and is capable of measuring bunches within a separation of 2 ns.The system is based on a direct-imaging optical system and high-speed photomultiplier array detector. A high-bandwidth linear signal amplifier and acquisition module have also been designed to process bunch-by-bunch multichannel signals from the detector. The software resampling technique and principal component analysis method were developed to obtain the synchronized data and enhance the signal-to-noise ratio. The fast injection of transients was successfully captured and analyzed. Moreover, the bunchby-bunch positions and sizes exhibited strong oscillation after the injection at the horizontal betatron oscillation frequency of the SSRF storage ring, and this demonstrated the bunch-by-bunch measurement capability of our system.

Space Charge Effect of Bunched Beam With Gaussian Distribution

The nonlinear space charge effect of a bunched beam with Gaussian distribu-tion in the longitudinal direction is discussed.Some useful formulae are derived for cal-culating the potential induced by a cylinder model of space charge in the waveguide of alinac with different combinations of density distribution:Gaussian distribution in thelongitudinal direction versus Kapchinskij Vladimirskij,waterbag,parabolic andGaussian distribution in the transverse direction,rcspectively.

Monitoring the charge bunch-by-bunch for the SSRF storage ring:Development and application

Bunch charge uniformity controlling is very important for top-up operation of the storage ring.In order to monitor filling pattern and measure the bunch charge precisely,a PXI waveform digitizer-based data acquisition system has been developed to retrieve bunch charge information from BPM pickup signals.An effective sampling rate is extended to 400 GHz by waveform rebuilding technology,which overlays multi-turn data into single turn with real time sampling rate of 8 GHz.An on-line evaluation indicates that resolution and linearity of the charge measurement are better than 0.5% at input range of 0.5-12nC.

Baseline recovery method to measure bunch charge under low-current mode of SSRF

The top-up injection mode of Shanghai Synchrotron Radiation Facility(SSRF) needs precise measurement of the beam bunch charges.This is performed by an integration current transformer,but the beam current is too low to neglect the background noise.In order to wipe out the noise coming from the ground loops,the adaptable polynomial fitting method is used to extract the baseline,instead of using the constant background or the linear background model. Test results show that the system resolution can be improved to <3%.

Touschek lifetime study based on the precise bunch-by-bunch BCM system at SSRF

Continuous tracking of bunch charges is the key to maintain stable operations in a storage ring in top-up mode. Recently, a precise bunch-by-bunch beam-current measurement (BCM) system has been developed at the Shanghai Synchrotron Radiation Facility. To avoid the influence of longitudinal oscillation on the amplitudes of the sampling points, a method called two-point equilibrium sampling is introduced. The results, obtained during routine operation time, show that the relative resolution of the measurement of the bunch charges is better than 0.02%. With this high resolution, the new BCM system is able to monitor the bunch-by-bunch beam lifetime. By using the filling pattern information, the Touschek lifetime and the vacuum lifetime can also be calculated. In this paper, the principle of the new method and the experiments is presented in detail.

Numerical simulation for space charge dominated beam transport

To simulate the intense bunched beam transport, a computer program LEADS-3D has been developed. The particle trajectories are analysed with the Lie algebraic method. The third order approximation of the trajectory solutions is made with space charge forces off, and the second order approximation is made with space charge forces on. The particle distribution in the 3D ellipsoid is uniform or Gaussian. Most of the conventional beam optical elements are incorporated in the code. The optimization procedures are provided to fit the beam lines to satisfy the given optical conditions.

Stress arch bunch and its formation mechanism in blocky stratified rock masses

Stress arch is a common phenomenon occurring in continuous materials and has also l：een proved to have great influences on the self-stabilization of soils or rock masses after excavation. In this paper, based on UDEC simulation, stress redistribution after excavation is investigated for a kind of special discontinuous material, i.e. blocky stratified rock mass. A layered stress arch system is observed with each stress arch lying over another. This special phenomenon is defined herein as ＂stress arch bunch＂. Effects of dip angle of bedding plane, lateral pressure and joint offset on this stress arch bunch are studied. Its formation mechanism is also discussed based on voussoir beam theory.

Fast-bunching design of compact heavy ion RFQ linac

We propose the construction of a compact linac as the injector of a cancer therapy facility at the Institute of Modern Physics(IMP) of the Chinese Academy of Sciences(CAS). Based on a traditional setup, a new compact fast-bunching design is first introduced to optimize the 600 keV/u RFQ with a 0.05 pm A ^(12)C^(4+) beam. This shortens the RFQ structure length from the standard design value of272–230 cm while effectively regulating the particle loss and emittance growth. In addition, a detailed error analysis was performed after the optimization process. The error sources cover input beam parameters errors, machining errors and alignment errors. The simulation results show that the beam loss and emittance growth of the RFQ are acceptable and within typical ranges of error.

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.

Beam instrumentation and diagnostics for HLS

The beam diagnostic instrumentation for the Heifei Light Source (HLS)is described. It provides sufficient parameters for machine study during the commi-sioning and common operation. The measured results are presented.

电子储存环逐束团诊断技术研究进展

相比于目前在电子储存环中广泛应用的逐圈束流诊断技术,逐束团诊断技术能够对每一个束团进行测量与分析,更有助于充分了解束流内部的状态,测量结果更接近真实的物理模型。近年来,束流信号采集设备的发展与信号处理算法的进步为逐束团诊断技术的不断发展奠定了基础。本文简述了逐束团诊断技术的基本原理和架构,简要介绍了国内外主要研究组在此方向上的探索性工作和研究成果,重点介绍了上海光源研究团队的研究路线、目前的研究成果以及在应用技术中的探索,并讨论了后续值得关注的研究方向和发展趋势,为同样致力于束流测量领域的研究者提供有价值的思路。

C波段2MeV驻波加速管物理设计

为了发展结构紧凑、小束斑加速器,进行了C波段驻波电子直线加速器加速管的物理设计和研究。利用多级聚束和大孔径注入方法,抑制空间电荷效应。加速管由3个聚束腔和4个加速腔组成,长约163mm,馈入微波功率源1MW。在最终的数值模拟中,得到脉冲电流约150mA,俘获效率优于30%,在加速管出口外约14mm处,对电子的横向分布进行非线性Gauss拟合,得到束斑直径(FWHM)约为0.55mm。

基于示波器嵌入式IOC技术的逐束团位置监测系统研制

为研究尾场引起的束团不稳定性,本工作开发了基于高速宽带示波器嵌入式IOC的逐束团位置测量系统。该系统通过直接获取加速器储存环中钮扣型电极的原始束流信号,进行在线计算独立的水平和垂直方向的逐束团位置。介绍了此系统的需求分析、硬件结构以及嵌入式IOC软件结构。利用在上海光源储存环上获取的逐束团位置数据,对系统性能进行了评估。实验显示,不同束团感应到的工作点及横向振荡振幅与束团编号间的依赖关系,结果证明该系统是一个有效的机器研究工具。

扩展互作用谐振腔的模拟分析

分析了扩展互作用谐振腔的工作原理、特点以及工作过程，并利用PIC粒子模拟程序对其进行了数值模拟，分析了阴极电压、电子注半径、谐振腔个数以及谐振腔周期长度对输出功率、频率及转换效率的影响。结果表明：当阴极电压为28．5～30．0kV时，谐振腔能正常工作；当电子注半径为1．4mm，谐振腔个数为4，阴极电压为29kV时输出功率和转换效率最大，输出功率为128kW，频率12．9GHz，转换效率达37．93％；输出频率随谐振腔周期长度的变小而增大。

超导加速器CW模式的高阶模初步分析

超导加速器由于具有极高的Q值,因此表现出较强的腔束相互作用,尤其是在以CW模式运行下,严重时会产生束流崩溃(BBU)效应。德国TESLA式的9 cell超导串腔在束流负载为1 mA,束团重复频率为81 25 MHz情况下,对其高阶模的产生及相应的功率水平进行了分析。结果表明:对于该腔的主要高阶模,谐振偏差值在π/4以上,束流没有发生谐振,高阶模功率在mW量级。

合肥光源逐束团测量系统研制

逐束团测量装置属于宽带和实时测量,足以分辨重复频率为204 MHz的相邻束团的信号,设计功能包括横向水平和垂直Beta振荡,纵向同步相位振荡,束团填充等信息的实时检测。对信号频谱分析,系统参数设计,前端射频检测,锁相环信号合成,高速数据采集以及基于PXI的整个系统作了详细介绍,分析了若干调试和实验结果,并讨论了合肥光源储存环目前存在的不稳定性及该测试手段在诊断中的应用。