L波段射频加速器电子束微脉冲诊断

 利用切伦柯夫辐射的瞬时发光机理，把相对论电子束打在熔石英靶片上转化为可见光，再用皮秒扫描相机进行测量，就可得到射频直线加速器皮秒电子束微脉冲的峰值电流及微脉冲束团。采用该方法，对L波段射频直线加速器的电子束微脉冲宽度和束团结构进行了诊断。由此构建了一套加速器电子束微脉冲的在线测量系统，该系统对调整加速器工作状态、提高束流品质使之适应自由电子激光要求起到了重要作用。     

皮秒扫描相机在加速器研究中的应用──监测电子束团的纵向分布

本文描述了一台基于皮秒扫描机机的电子束团纵向分布(电子束团长度)测试系统,报道了应用这套系统在中科院高能物理所北京自由电子激光装置(BFFL)S波段射频直线加速器、正负电子对撞机(BEPC)和中国原子能科学研究院L波段注入器(LBINJ)上开展的测量工作.     

北京正负电子对撞机同步辐射光脉冲形状的高分辨率测量

用国产BWS-5kII型皮秒扫描相机测量了北京正负电子对撞机(BEPC)上极端相对论性运动正负电子束团产生的同步辐射光脉冲的时间结构、光脉冲长度与电子束流强度以及射频源电压的关系.当负电子束流强度由2mA增加到30mA时,光脉冲长度由220ps增加到670ps;在20mA电子束流强度条件下,射频源电压由250kV增加到500kV时,光脉冲长度在500ps到700ps范围内变化.测量系统的时间分辨率为30ps;时间刻度误差±15%,触发晃动小于±200ps.     

一种在线式电子束能量测量方法

针对直线感应电子加速器中的束流特点,设计了一种在线式电子束能量测量方法。该方法使用分析磁铁和束位置探测器对电子束团切片平均能量进行测量,避免了束团取样带来的误差及测量过程对束流的影响,可以实现电子能量的在线测量。使用该方法对某强流直线感应电子加速器的电子束团能量进行了测量,获得了电子束团切片平均能量随时间变化的曲线,能量测量不确定度为0.177 MeV,能散度测量不确定度为0.39%。     

电光采样(EOS)法测量超短电子束束团长度中的模拟计算与误差分析

随着高能物理的发?高能量正负电子对撞机,射线自由电子激光器,先进的同步光源等,都需要产生高流强超短脉冲的相对论电子束团.于是,亚皮秒电子束束团诊断成为加速器物理新发展的关键技术,电子束长度的监测是其中的一部分.电光采样(EOS)法测量超短电子束团长度有非侵入、非破坏、实时测量的特点,具有较好的应用前景.本文介绍该方法的原理,通过模拟计算分析电子束束团与探测光间距、电子束电场与电光晶体晶轴夹角、探测光偏振方向与电光晶体晶轴夹角等实验参数与束团长度测量的关系,做系统误差分析,对实际实验有指导意义.     

电光采样(EOS)法测量超短电子束束团长度中的模拟计算与误差分析

随着高能物理的发展, 高能量正负电子对撞机, X射线自由电子激光器, 先进的同步光源等, 都需要产生高流强超短脉冲的相对论电子束团. 于是, 亚皮秒电子束束团诊断成为加速器物理新发展的关键技术, 电子束长度的监测是其中的一部分. 电光采样(EOS)法测量超短电子束团长度有非侵入、非破坏、实时测量的特点, 具有较好的应用前景. 本文介绍该方法的原理, 通过模拟计算分析电子束束团与探测光间距、电子束电场与电光晶体晶轴夹角、探测光偏振方向与电光晶体晶轴夹角等实验参数与束团长度测量的关系, 做系统误差分析, 对实际实验有指导意义.     

射频远红外波导自由电子激光器的新特性

将射频调制的超短脉冲电子束理想化为一系列δ时间函数,提出了用波导本征模展开的方法计算波导自由电子激光器中超短脉冲电子束的相干同步辐射.结果发现当谐振频率等于直线加速器射频的整数倍时,辐射模式表现为”纯”的波导本征模另外分析了超短脉冲在矩形波导中相干发射的频率特性和滑移问题,最后推导了有一定脉宽的矩形脉冲对辐射波的增益解析式.     

“神龙一号”电子束时间分辨能谱测量新方案

介绍了"神龙一号"直线感应加速器电子束时间分辨能谱测量新方案——用螺线管磁场旋转束流法测量其出口电子束能谱,阐述了旋转束流法基本原理及测量方案设计,并且讨论了测量误差。此方案所测能谱为时间分辨离散型束流能谱,其误差与所测离散束流能谱相关。通过测量"神龙一号"加速器末端的电子束流在螺线管磁场中的旋转角度及角度展宽,从而得到脉冲电子束流能谱。     

神龙二号多脉冲电子束束参数的时间分辨测量技术

神龙二号是一台三脉冲强流脉冲电子束直线感应加速器,就其多脉冲的电子束束参数的测量而言,基本要求是单个脉冲可分辨,进一步的要求是脉冲内时间可分辨。基于光学渡越辐射原理及瞬态发射度测量系统原理,发展了一种束斑与发散角可以分开测量的光学布局结构,结合多台高速分幅相机,成功研制了一套完整的多脉冲电子束束参数的测量系统,其特点是灵活的组合测量方式,全面满足了神龙二号复杂艰难的调试及参数测量工作要求。测量系统最高时间分辨测量能力达到约2 ns的水平,单个脉冲可以获得至少8个时间分辨的束参数测量结果。     

强流脉冲电子束时间分辨测试技术研究

简单介绍了LIA注入器中强流脉冲电子束能谱分布及发射度的测量原理.应用变象管扫描相机测量了脉冲宽度为100ns的强流脉冲电子束的能谱分布及发射度两个参量,得到了具有时间分辨本领为1ns的切伦科夫辐射图像.为强流直线感应加速器的研制,提供了实验数据.     

Beam test of CSES silicon strip detector module

The silicon-strip tracker of the China Seismo-Electromagnetic Satellite(CSES) consists of two doublesided silicon strip detectors(DSSDs) which provide incident particle tracking information.A low-noise analog ASIC VA140 was used in this study for DSSD signal readout.A beam test on the DSSD module was performed at the Beijing Test Beam Facility of the Beijing Electron Positron Collider(BEPC) using a 400–800 MeV/c proton beam.The pedestal analysis results,RMSE noise,gain correction,and intensity distribution of incident particles of the DSSD module are presented.     

A proposed U.S./China theoretical/experimental collaborative effort on baryon resonance extraction

In this paper we discuss the reasons for our work towards establishing a new collaboration between Jefferson Lab （JLab） and the Institute of High Energy Physics （IHEP） in Beijing. We seek to combine experimentalists and theorists into a dedicated group focused on better understanding the current and future data from JLab and from the Beijing Electron Positron Collider （BEPC）. Recent JLab results on the extraction of single- and double-polarization observables in both the lπ- and 2π-channel show their high sensitivity to small production amplitudes and therefore their importance for the extraction of resonance parameters. The Beijing Electron Spectrometer （BES） at the BEPC has collected high statistics data on J/ψ production. Its decay into baryon-antibaryon channels offers a unique and complementary way of probing nucleon resonances. The CEBAF Large Acceptance Spectrometer, CLAS, has access to N＊ form factors at high Q2 which is advantageous for the study of dynamical properties of nucleon resonances, while the low-background BES results will be able to provide guidance for the search for less-dominant excited states at JLab. Moreover, with the recently approved experimental proposal Nucleon Resonance Studies with CLAS12 and the high-quality data streaming from BES-Ⅲand CLAS, the time has come for forging a new Trans-Pacific collaboration of theorists and experimentalists on NSTAR physics.     

A proposed U.S./China theoretical/experimental collaborative effort on baryon resonance extraction

In this paper we discuss the reasons for our work towards establishing a new collaboration between Jefferson Lab (JLab) and the Institute of High Energy Physics (IHEP) in Beijing. We seek to combine experimentalists and theorists into a dedicated group focused on better understanding the current and future data from JLab and from the Beijing Electron Positron Collider (BEPC). Recent JLab results on the extraction of single- and double-polarization observables in both the 1π- and 2π-channel show their high sensitivity to small production amplitudes and therefore their importance for the extraction of resonance parameters. The Beijing Electron Spectrometer (BES) at the BEPC has collected high statistics data on J/ψ production. Its decay into baryon-antibaryon channels offers a unique and complementary way of probing nucleon resonances. The CEBAF Large Acceptance Spectrometer, CLAS, has access to N~* form factors at high Q~2, which is advantageous for the study of dynamical properties of nucleon resonances, while the low-background BES results will be able to provide guidance for the search for less-dominant excited states at JLab. Moreover, with the recently approved experimental proposal Nucleon Resonance Studies with CLAS12 and the high-quality data streaming from BES-Ⅲ and CLAS, the time has come for forging a new Trans-Pacific collaboration of theorists and experimentalists on NSTAR physics.     

Search for invisible decays of eta and eta' in J/psi --> phi eta and phi eta'

Using a data sample of 58 x 10(6) J/psi decays collected with the Beijing Spectrometer II detector at the Beijing Electron Positron Collider, searches for invisible decays of eta and eta' in J/psi to phi eta and phi eta' are performed. The phi signals, which are reconstructed in K+K- final states, are used to tag the eta and eta' decays. No signals are found for the invisible decays of either eta or eta', and upper limits at the 90% confidence level are determined to be 1.65 x 10(-3) for the ratio B(eta-->invisible)/B(eta --> gamma gamma) and 6.69 x 10(-2) for B(eta' --> invisible)/B(eta' --> gammagamma). These are the first searches for eta and eta' decays into invisible final states.     

对北京正负电子对撞机阻抗的研究

比较全面地研究了北京正负电子对撞机(BEPC)的耦合阻抗并试图从降低耦合阻抗的角度来探讨压缩BEPC束长的可能性.     

Study of BEPC Impedance

The impedance of Beijing Electron positron Collider (BEPC) is studied in detail, and the possibility of suppressing bunch lengthening in BEPC is discussed in the view of decreasing the coupling impedance.     

BEPC能区强子事例形态特性及模拟

利用北京谱仪(BES)在3.55GeV附近采集的数据和国际上已发表的数据,研究了北京正负电子对撞机(BEPC)能区强子事例形态特征的分布,对LUND模型的JETSET7.4产生子作了仔细研究,并得到与低能实验数据相符的模型参数.     

A photon conversion finder at BESⅢ

A photon conversion finder (PCF) based on track information from the main drift chamber (MDC) of the Beijing Spectrometer (BES0) at the Beijing Electron Positron Collider (BEPC/) is developed. The validation of the PCF is done by reconstructing π⁰ and measuring the branching fraction of J/ψ →γη'. Using the developed PCF tool, we mapped the materials from the interaction point through the BEPCII beam pipe up to the inner wall of the MDC.     

BEPC中的电子云不稳定性研究

多束团正电子储存环中可能发生电子云不稳定性(ECI). 自1996年起, 在北京正负电子对撞机(BEPC)上开展了与这种束流不稳定性相关的系列研究. 文章扼要介绍在BEPC上进行的电子云不稳定性研究, 包括实验观测和模拟计算, 并讨论可能的抑制措施.     

BEPC Compton散射极化仪的理论研究

简要介绍了圆偏振激光在极化电子束上的Ｃｏｍｐｔｏｎ散射理论,研究了北京正负电子对撞机（ＢＥＰＣ）极化仪的测量原理,并根据ＢＥＰＣ极化仪的实验参数计算了散射的能谱、空间分布和强度．The theory of Compton scattering of polarized photons on polarized electrons, and the principle of Beijing Electron Positron Collider (BEPC) Compton polarimeter are shortly discussed. The energy spectrum, vertical distributions and the intensity of Compton scattering under particular conditions are also calculated.