不同强度射线源工业CT扫描参数优化研究

以含有不同强度射线源的高精度工业CT设备为研究对象，开展了投影数K与每个角度投影测量次数M等扫描参数优化配置的研究。建立了Matlab扇束CT仿真平台，基于不同扫描参数，模拟了不同射线强度下的CT投影与重建仿真，并采用人眼主观评价及CT重建图像客观评价相结合的方法对仿真图像质量进行了评估，给出了在限定检测时间条件下的扫描参数K、M优化配置准则及相应计算公式。在包含X光机和⁶⁰Co两种不同射线源的高精度工业CT设备上开展了锥束CT验证试验，试验结果表明，CT扫描参数优化方法及公式可行有效，为高精度工业CT检测设备的优化使用提供了一种技术手段。     

基于电子束扫描阵列微焦点射线源的倒置结构Micro-CT成像研究

倒置几何结构CT成像系统理论上具有扫描视场大、图像信噪比好、锥束伪影小等优点,但其多焦点、稀疏角的扫描模式亦会带来投影数据截断、稀疏和局部数据冗余等问题。本文利用电子束扫描阵列微焦点射线源和高分辨率小面积探测器等构建了一种新型高分辨率、大视场的倒置几何结构Micro CT实验系统(IG Micro CT)。针对该系统多焦点、稀疏角扫描模式下的投影数据截断和稀疏等特点,提出一种图像先验约束的全变分正则化SART迭代CT图像重建算法。首先通过仿真实验对图像重建算法进行了验证,并对阵列微焦点数量、旋转扫描分度数量等扫描参数进行优化,最后在IG Micro CT实验系统上获得了高分辨的Micro CT测试图像。实验结果表明,本文提出的算法适用于IG Micro CT系统,解决了投影数据截断、稀疏采样和局部数据冗余带来的条状等伪影问题,并验证了IG Micro CT这种新型成像方式的可行性。     

静态CT行包安检系统关键技术研究

本文介绍了安检用静态CT技术的基本原理,对基于超顺排碳纳米管技术的冷阴极X射线源、基于光子计数技术的多能谱X射线成像技术和安检用静态CT系统图像重建算法等进行了研究。冷阴极X射线源由基于超顺排碳纳米管技术的冷阴极X射线管、两套高压系统和1个控制系统组成,在130 kV以下可稳定工作。研制并测试了一款具有三能谱成像功能的光子计数型X射线探测器系统。对安检用静态CT系统图像重建算法进行了讨论,提出了一种解决方法。安检用静态CT系统关键技术的研究为安检用静态CT系统的研制提供了技术基础。     

X射线源针孔成像方法可行性研究

为检验利用针孔成像对X射线源进行研究的可行性，对X射线针孔成像系统进行优化设计，搭建了1套X射线源针孔成像装置。从理论上对X射线源的位置和强度发生变化时图像的相应变化进行了计算和预估，并用实验加以验证。结果表明，像斑中心位置的移动和像斑灰度值的变化分别与X射线源位置和强度的变化在一定范围内存在线性关系，由此证明了利用针孔成像对X射线源进行空间定位及定量研究的可行性。本文结果对X射线源针孔成像的系统设计具有参考意义。     

高能工业CT用4MeV加速器的研制

X射线CT检测技术通过投影重建方法获取被检测物体的数字图像，解决了传统X射线透视成像中影像重叠、密度分辨率低等缺点。ICT（工业CT）是一种重要的无损检测工具，能紧密、准确地再现物体内部的三维立体结构，能定量地提供物体内部的物理、力学特性，如缺陷的位置及尺寸、密度的变化，异型结构的形状及精确尺寸，物体内部的杂质及分布等。     

基于重投影的CT图像硬化伪影校正

在工业计算机断层成像(CT)技术中所用的X射线源通常是多能的,检测过程中只能获得多能投影数据,若直接重建图像则会出现硬化伪影,硬化伪影校正是提高重建图像质量的一重要步骤。本文采用重投影的方法来校正由于射线硬化导致重建图像出现的硬化伪影,通过硬化校正后的重建CT图像质量得到显著提高。     

基于DICOM标准的微焦点辐射图像采集与传输

微焦点X射线成像设备FXS-160包括微焦点X光机、图像增强器、5个运动自由度物品台等,适合于检测集成芯片、电路板、小型器件等,在监视器上可实时获得物体的透视图像。以微焦点X射线成像设备为基础,开发遵循DICOM标准的小型PACS系统,完成微焦点X射线图像的采集与传输,提供了一个可扩展性强、架构灵活的辐射成像实验平台,并为辐射成像工业应用标准的建立进行了有益的尝试。     

X射线源焦点尺寸的测试与对比分析

射线源焦点的大小与形状对射线检测图像质量有重要的影响,但在射线检测中却很少对射线源焦点进行实测,这不利于准确控制射线检测图像质量。对射线源焦点的测量方法进行对比试验分析,以获得对射线源焦点进行评估的有效便捷方法。分别应用小孔成像板、星形测试卡、双线型像质计(Image quality indicator,IQI)等测试体,对工业应用的便携式X射线机进行了焦点尺寸测量。用星形测试卡、双线型像质计所测算的焦点尺寸一致性较好,但较之小孔成像的测量结果却存在较大偏差。实际检测时射线机焦点大小可能与标称值明显不同,有必要对射线焦点特性进行及时评价;双线型像质计可一定程度上代替星形测试卡的使用,便捷地实现图像不清晰度的测量、射线源焦点尺寸的评估。     

平板X射线源重叠投影的线性迭代重建

为解决平板X射线源多个射线源同时照射时产生的投影重叠问题带来的图像重建困难,本研究提出了一种基于平板X射线源重叠投影的CT图像重建方法。该方法引入线性修正因子修正投影重叠带来的非线性,然后使用联合代数重建算法(SART)实现CT图像的重建。实验表明,该方法可以实现平板X射线源重叠投影直接重建CT图像,但是随着平板X射线源阵列数增大,重建图像质量下降。     

高能旋转物体CT随机投影的角度识别

介绍一种高能旋转物体CT(HeroCT)随机投影的角度识别研究。采用ns和μs闪光X射线，对高能旋转物体进行透射可以获取一系列瞬时投影。在闪光无法与旋转物体角移严格同步时，为进行CT图像重建，需对这些随机投影的投影角进行识别和确定其在正弦图上的位置。利用计算机模拟，对投影角识别方法进行了研究。     

Beam and image experiment of beam deflection electron gun for distributed X-ray sources

Distributed X-ray sources comprise a single vacuum chamber containing multiple X-ray sources that are triggered and emit X-rays at a specific time and location. This process facilitates an application for innovative system concepts in X-ray and computer tomography. This paper proposes a novel electron beam focusing, shaping,and deflection electron gun for distributed X-ray sources.The electron gun uses a dispenser cathode as an electron emitter, a mesh grid to control emission current, and two electrostatic lenses for beam shaping, focusing, and deflection. Novel focusing and deflecting electrodes were designed to increase the number of focal spots in the distributed source. Two identical half-rectangle opening electrodes are controlled by adjusting the potential of the two electrodes to control the electron beam trajectory, and then, multifocal spots are obtained on the anode target. The electron gun can increase the spatial density of the distributed X-ray sources, thereby improving the image quality. The beam experimental results show that the focal spot sizes of the deflected(deflected amplitude 10.5 mm)and non-deflected electron beams at full width at half maximum are 0.80 mm 90.50 mm and 0.55 mm 90.40 mm, respectively(anode voltage 160 kV; beam current 30 mA). The imaging experimental results demonstrate the excellent spatial resolution and time resolution of an imaging system built with the sources, which has an excellent imaging effect on a field-programmable gate array chip and a rotating metal disk.     

Dependence of PXR beam performance on the operation of the pulsed electron linac

Advanced applications of parametric X-ray radiation (PXR) such as energy-dispersive X-ray absorption fine structure (DXAFS) analysis and phase-contrast imaging have been developed at the Laboratory for Electron Beam Research and Application (LEBRA) of Nihon University. To improve the electron beam quality and geometrical stability of the target crystal, the cooling-water system for the linac and the PXR target was replaced with a new one capable of more precise control. As a result, the reliability of the experimental data in PXR applications, especially in X-ray imaging, has improved. The effect of the electron beam focusing on the target crystal was also investigated. The results of X-ray imaging with a long propagation distance and measurement of the time-structure of the PXR intensity suggest that the correlation between the electron beam profile and the X-ray coherence is rather complicated. It is possible that incident electrons cause some deformation of the target crystal, becoming the dominant factor restricting the quality of intense PXR.     

Ultra fast electron beam X-ray computed tomography for two-phase flow measurement

Electron beam X-ray CT is a new technique for a fast measurement of multiphase flows with frame rates of 1000 images per second and more. It gives, in principle, quantitatively accurate images of the flow at high spatial resolution and it is non-intrusive since moderately radiation absorbing vessel walls can be penetrated by X-rays. However, on the road to a technical realisation of such a technique within a computed tomography system many problems have to be solved. As a first prototype for scientific flow measurement studies, we devised and built a fast scanned electron beam X-ray tomography scanner. The scanner consists of an electron beam unit that can be operated at up to 150 kV acceleration voltage and up to 65 mA electron beam current, with the required electron optics for beam adjustment, beam focusing and beam deflection unit and a fast circular CZT detector comprising 240 elements of 1.5 mm × 1.5 mm × 1.5 mm active pixel area. X-ray radiation is produced on a circular water cooled tungsten target. The CT system achieves up to 7000 frames per second with a spatial resolution of 1 mm. First two-phase flow experiments have been carried out on gas-water flows in bubble columns. Further, a vertical test section made of titanium alloy has been installed at the TOPFLOW facility and will be used in future to study the evolution of two-phase gas-water pipe flow at high pressures and temperatures.     

一个基于EPICS框架的EPU前端反馈系统

插入件是现代光源重要组成设备之一,其质量直接影响上海光源整体性能。由于建造和安装工艺的限制,插入件的磁场会对束流轨道稳定性产生影响。为降低对束流的扰动,在插入件电子束流入口和出口位置增加校正线圈实现自动补偿功能。因此我们设计了基于EPICS的插入件前端反馈系统,经测试,该前馈系统用户界面简洁,反馈控制功能完整可靠,实时性高,提高了束流的稳定性,为试验站稳定供光提供了保证。     

Numerical simulation and experiment of error field measurement using luminous trace of electron beam in SST-1

In contrast to the earlier experiments conducted in other machines,here,in SST-1 the error field measurement experiment is performed with a filled gas pressure ～8×10~(-4) mbar which helped to create a luminescent toroidal beam of electron path originated due to impact excitation and guided by the toroidal magnetic field.Beam path deviations are observed and recorded from radial and top ports using visible range cameras.Such creation and detection of the electron beam path differs from the earlier works where the gun emitted electron beam deviation in ultrahigh vacuum was detected on a collector-grid/fluorescent screen.In the present experiment,large beam deviations were observed.Later investigation of the experimental set-up reveals existence of a possible source of radial electric field in between the source and the vacuum vessel which are separately grounded.Thus,to understand the observed phenomena,experiments are numerically modeled with deviated TF coil set,PF coil set and the electron source location.A particle tracing code is used to follow the electron path in the magnetic field generated by the coil set of interest.Simulation results suggest that the large deviation corresponds to the E×B drifts and not due to the large field errors.Toroidally averaged field errors of the SST-1 TF coils at toroidal field of B_0=15 kG are negligibly small～B_0×10~(-6) or less,which should not adversely affect the plasma performance.     

关于扫描电子束的均匀性

电子加速器的主要用途是用作辐射源。然而,从加速器中引出来的电子束的束流密度太大,一般不能直接用来辐照样品,而要用扫描仪把电子束扫开。扫描后的电子束分布应力求均匀,但事实上并非如此。本文认为用三角波磁场扫描引起束流密度不均匀的原因之一是涡流造成的。     

Beam dynamics design of an SP-FEL compact THz source

In recent years, people are looking for a new compact THz source with high emission power, one potential choice is to build small accelerator with Smith-Purcell radiation. The main difficulty is how to obtain high quality electron beam. In this paper, the beam dynamics design of a compact THz source is presented. The electron beam is produced by an electron gun and compressed by permanent magnets. The electron gun is similar to the Shanghai EBIT,but permanent magnets are used, instead of the superconducting magnets in Shanghai EBIT. With this design, we can reduce the size and cost of the whole device. Poisson/Pandira was employed to simulate and optimize the magnetic field. Egun was used to simulate the beam trajectories from the electron gun to the collector. Within 2 centimeters around the center of longitudinal magnetic field, the calculation showed that the beam satisfies to our design aim.     

电子束真实发射度测量原理

描述了一个新的发射度测量方法.它包括有磁扫描系统,厚窄缝,荧光屏以及CCD图像处理系统.这个方法能够测量出电子束的真实发射度图形.文章设计了磁扫描系统,估计了束流通过磁扫描系统引起的发射度增长,还讨论了为阻挡高能电子穿透,窄缝必须选择的厚度.电子束发射度的测量对于自由电子激光以及其它对束流品质要求较高的加速器装置都是很重要的.