多狭缝法测量激光尾场电子束发射度的模拟研究

发射度是描述束流品质的重要物理量,根据发射度和传输矩阵可以准确计算束流包络和发散角的变化。在考察传统加速器束流发射度测量方法的基础上,提出采用多狭缝法对激光尾场产生的电子束发射度进行测量。采用宽度为20 m的多狭缝板对发射度为0.05 mmmrad的激光尾场加速电子发射度进行测量,数值模拟结果表明采用多狭缝法测量的相对误差可以控制在5%以内。并给出了不同狭缝参数对测量精度的影响,模拟结果表明狭缝宽度对发射度测量精度影响最大。狭缝宽度越窄,测量精度越高,反之,则越低。     

高亮度注入器取得进展

1993年8月18日,高亮度注入器课题组邀请王淦昌教授,陈能宽教授,杜祥琬首席科学家,陈佳洱教授和王乃彦教授,对中国原子能科学研究院研制的L波段高亮度注入器进展情况进行了检查并观看了现场测试情况。测试结果表明:微脉冲束流目前可达84A,超过了25A的设计指标;在微脉冲流为46A时,归一化发射度     

合肥软X射线波段自由电子激光注入器模拟优化

合肥软X射线波段自由电子激光项目是基于直线加速器的软X射线光源. 其注入器由光阴极微波电子枪与两个直线加速3米段构成. 光阴极微波电子枪产生束团电荷量1nc、峰值流强100A、重复频率10Hz电子束流, 并利用螺线管磁场在其出口处进行发射度补偿, 在经过一段漂移距离后电子束流进入增强直线段加速. 使在低能端由于空间电荷效应产生的横向发射度增长基本被完全补偿. 本文中利用PARMELA对注入器进行了模拟计算, 对发射度的补偿效果进行了优化, 同时对注入器内各元件的布置也进行了优化. 在注入器出口可以得到归一化横向发射度小于1.5mm.mrad的低发射度束流.     

光阴极微波电子枪驱动激光整形与传输系统

为满足合肥先进光源对高品质注入束流的要求,合肥先进光源预研项目研制了一套光阴极微波电子枪系统作为注入器电子源。为降低空间电荷效应引起的束流发射度增长,对驱动激光整形及传输系统进行了理论和实验研究。通过双折射晶体的脉冲时间整形以及采用光阑高斯截断的空间整形,得到了近似均匀分布的激光脉冲。像传递激光传输光路,实现了光阴极表面激光位置的高稳定性。实验结果显示,光阴极表面的激光位置抖动小于4 μm,激光性能满足实验要求。     

三种高密度强流束亮度测量技术

利用已经建成的4 MeV LIA注入器,结合时间分辨测量系统研究了三种测量技术:发射度测量法、无场准直器和磁场准直器测量法。介绍了强流束亮度定义和典型方法理论分析及测量技术的物理概念,提出了用于猝发多脉冲电子束发射度测量装置的设计与调试,通过对时间分辨测量系统的分幅相机记录的光强度分布信息处理,得到电子束束斑均方根半径和发射角,分析某一时刻数据,即可得到电子束某一时刻发射度,从而获得多脉冲电子束时间分辨发射度。在4 MeV LIA注入器上对多脉冲电子束流的发射度进行测量,得到电子束归一化均方根发射度约为114 mmmrad、双脉冲456 mmmrad的归一化发射度。最后结合电子束的高斯分布初步分析并给出均方根发射度、实测发射度和边发射度的关系。     

用修正三梯度法测量束流发射度

 介绍了修正三梯度法的原理和利用该方法测量发射度的实验装置。编写了基于束包络方程的数值拟合程序，并进行了模拟计算。用修正三梯度法对3.5MeV注入器出口处脉冲电子束的发射度做了时间分辨的测量。结果表明，当空间电荷力不可忽略时，该注入器输出的电子束脉冲期间中间部分束的发射度为1 040π·mm·mrad。     

基于合肥先进光源的准直参考网络机械系统设计及其仿真分析

新一代粒子加速器中磁铁位置与姿态的准确测量和安装依赖于各项技术的综合运用。实现磁铁在全局坐标系中准确定位,并且快速精密安装测量,为了建造高亮度、低发射度的第四代同步辐射光源,国家同步辐射实验室开展了"合肥先进光源(HALF)"的预研工作。作为准直测量系统的重要研究内容,创新性地提出了准直参考网络方法。为了保证准直测量精度,对准直参考网络的机械系统本身的形变要求很高,通过ANSYS软件对机械系统整机进行了静力学仿真,根据分析结果对准直基准板进行了优化设计,使其满足工作条件要求。     

粒子束团状态对测量束流发射度及能量的影响

为了验证国产质子注入器的参数是否满足需求,注入器团队设计了束流测量系统用于测量国产质子直线注入器束流的流强、发射度、能量以及能散等关键指标。此测量系统包含了采用变聚焦法测量发散度、采用分析磁铁测量束流能量和能散的主要功能。利用束流输运线设计软件Tracewin(版本2.11.4.1)进行了系统束线的物理设计,对束测系统测量质子束流的发散度和能量的精度进行了模拟计算。由于经过RFQ-(APF)DTL加速后的粒子束团为“拖尾”的非理想粒子束团,需要针对非理想束团对束测系统测量发射度和能量产生的影响进行分析。通过对模拟计算结果的分析,发现相对于测量理想粒子束团的结果非理想粒子束团对束测系统测量发射度精度影响较大;非理想粒子束团对束测系统测量能量精度影响较小。     

RF腔光阴极注入器中热发射度的测量研究

论文介绍RF腔光阴极注入器中热发射度的测量方法，在注入器中有三个因素影响热发射度的测量，它们是：射频场效应、空间电荷效应和发射度测量误差. 在注入器出口处，电子束发射度由：热发射度、射频场效应引起的发射度增长和空间电荷效应的发射度增长三部分组成. 论文从注入器中发射度增长理论和模拟出发，给出了一个能够消除射频场效应和空间电荷效应的热发射度测量方法.     

合肥光源上采用干涉方法测量束流截面

 束流截面尺寸测量对优化系统参数、确保光源运行至关重要。采用干涉法测量合肥同步辐射光源束流截面垂直方向的尺寸。基于Cittert-Zernike 定理,利用双缝干涉条纹的对比度得出相干度和束流截面尺寸。测量系统由干涉成像与图像处理系统组成。进行了5组试验,试验结果证明了干涉法测量合肥同步辐射束流截面尺寸的可行性。     

A fast emittance measurement unit for high intensity DC beam

A combined unit, which has the ability to measure the current and emittance of the high intensity direct current(DC)ion beam, is developed at Peking University(PKU). It is a multi-slit single-wire(MSSW)-type beam emittance meter combined with a water-cooled Faraday Cup, named high intensity beam emittance measurement unit-6(HIBEMU-6). It takes about 15 seconds to complete one measurement of the beam current and its emittance. The emittance of a 50-mA@50-kV DC proton beam is measured.     

A method to measure the nonlinear force caused emittance growth in a RF photoinjector

Based on the multi-slit method, a new method is introduced to measure the non linear force caused emittance growth in a RF photoinjector. It is possible to reconstruct the phase space of a beam under some conditions by the multi-slit method. Based on the reconstructed phase space, besides the emittance, the emittance growth from the distortion of the phase space can also be measured. The emittance growth results from the effects of nonlinear force acting on electron, which is very important for the high quality beam in a RF photoinjector.     

An emittance measurement device for a space-charge dominated electron beam

Beam emittance is one of the most important parameters for electron sources. To investigate the beam emittance of the 3.5-cell DC-SC photocathode injector developed at Peking University, a multi-slit emittance measurement device has been designed and manufactured. The designed slit width, mask thickness and beamlet drift length are 100 μ m, 3 mm and 430 mm respectively. It is suitable for the electron beam with energy of about 5 MeV and the average current less than 0.1 mA. The preliminary measurement result of the rms emittance of the electron beam produced by the DC-SC injector is about 5-7 mm·mrad.     

合肥光源新的束团截面及发射度测量系统的研制

介绍了合肥光源储存环紫外光束团截面及束流发射度测量系统. 本系统采用光学探测, 由光学成像和图像采集处理两大部分组成. 光学成像部分利用光学成像将中心波长366.1nm紫外光1:1成像于CCD探测器上. 图像采集处理部分将CCD探测器采集的视频信号由电缆输出到图像采集卡进行图像采集, 然后由LabVIEW程序进行数据处理获得束团截面尺寸以及束流发射度和耦合度, 最后给出了实验结果.     

Multi-Slit Diffraction of Evanescent Electromagnetic Waves

The well-known Fraunhofer multi-slit diffraction is described as the multi-slit interference modulated by the singleslit diffraction, namely the multiplication between the single-slit diffraction factor and the multi-slit interference factor. By considering the simplified argument we show that the multi-slit diffraction of evanescent waves which are in the near-field region also has the interference and diffraction effects, and that this two-fold effect can be expressed as the convolution of the diffraction factor and the interference factor. Our conclusion could be helpful to understand the contribution of evanescent waves to the optical responses of sub-wavelength structures such as slits and grooves.     

HLSⅡ干涉法测量储存环横向尺寸与发射度

为了满足合肥光源升级改造后测量小束流尺寸的需求,设计了干涉法测量束团尺寸与发射度系统。简要介绍了在可见光波段利用干涉法测量束团横向尺寸的原理,详细介绍了该系统的光路与软硬件系统和图像处理算法。为了消除CCD的本底噪声对测量的影响,建立了本底噪声图像与束流流强的查找表,最终得到了多束团模式下的在线实验结果。测量得到的水平尺寸为265μm,测量误差为5.78μm;垂直尺寸为114μm,测量误差为4.89μm。     

High-resolution imaging of a long-distance target with a single-slit streak-tube lidar

Streak-tube lidar (STIL) is an excellent laser-imaging system, which can provide a high-resolution 4D-image. Compared to multi-slit STIL (MS-STIL), single-slit STIL (SS-STIL) can offer much higher image resolution using beam compression. This advantage is important for identification of a long distance target. We propose a method for increasing the SS-STIL-system resolution and perform an experiment on high-resolution imaging of a long-distance target. Since the beam-compression rate is limited due to the resolution of the streak-tube photocathode, we propose a method for defining the proper laser-beam shape in the STIL-system design.     

Instantaneous electron beam emittance measurement system based on the optical transition radiation principle

One kind of instantaneous electron beam emittance measurement system based on the optical transition radiation principle and double imaging optical method has been set up. It is mainly adopted in the test for the intense electron-beam produced by a linear induction accelerator. The system features two characteristics. The first one concerns the system synchronization signal triggered by the following edge of the main output waveform from a Blumlein switch. The synchronous precision of about 1 ns between the electron beam and the image capture time can be reached in this way so that the electron beam emittance at the desired time point can be obtained. The other advantage of the system is the ability to obtain the beam spot and beam divergence in one measurement so that the calculated result is the true beam emittance at that time, which can explain the electron beam condition. It provides to be a powerful beam diagnostic method for a 2.5 kA, 18.5 MeV, 90 ns (FWHM) electron beam pulse produced by Dragon I. The ability of the instantaneous measurement is about 3 ns and it can measure the beam emittance at any time point during one beam pulse. A series of beam emittances have been obtained for Dragon I. The typical beam spot is 9.0 mm (FWHM) in diameter and the corresponding beam divergence is about 10.5 mrad.