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。     

Improved ultrasonic testing by phased array technique and its application

The phased array ultrasonic testing method is available for beam steering and focusing, and then the focused beam divergence angle can be narrowed and the sound level can be intensified at the focused region. In the present study, two examples of phased array application which are the linear scanning mode operation and the sector scanning mode operation, were conducted in order to establish the availability of this technique as an actual NDT technique. As the result of the experiments, it was recognized that both types of scanning mode had the capability for defect detection and successful estimation of the defect size. Furthermore, it was well realized that the real time B-scope display without mechanical scanning was effective to reduce the operating time of inspection.     

Wave propagation visualization in an experimental model for a control rod drive mechanism assembly

Nondestructive inspection techniques such as ultrasonic testing, eddy current testing, and visual testing are being developed to detect primary water stress corrosion cracks in control rod drive mechanism (CRDM) assemblies of nuclear power plants. A unit CRDM assembly consists of a reactor upper head including cladding, a penetration nozzle, and J-groove dissimilar metal welds with buttering. In this study, we fabricated a full-scale CRDM assembly mock-up. An ultrasonic propagation imaging (UPI) method using a scanning laser ultrasonic generator is proposed to visualize and simulate ultrasonic wave propagation around the thick and complex CRDM assembly. First, the proposed laser UPI system was validated for a simple aluminium plate by comparing the ultrasonic wave propagation movie (UWPM) obtained using the system with numerical simulation results reported in the literature. Lamb wave mode identification and damage detectability, depending on the ultrasonic frequency, were also included in the UWPM analysis. A CRDM assembly mock-up was fabricated in full-size and its vertical cross section was scanned using the laser UPI system to investigate the propagation characteristics of the longitudinal and Rayleigh waves in the complex structure. The ultrasonic source location and frequency were easily simulated by changing the sensor location and the band pass filtering zone, respectively. The ultrasonic propagation patterns before and after cracks in the weld and nozzle of the CRDM assembly were also analyzed. Since this visualization method is not limited in the flat cross section, it will be useful in developing ultrasound-based structural health monitoring technologies, advanced nondestructive methods, and numerical models. In addition, the proposed laser UPI system could be a useful tool in optimizing the receiver and transmitter locations, the ultrasonic path, and the ultrasonic frequency.     

Measurements of the acoustic field on austenitic welds: a way to higher reliability in ultrasonic tests

In nuclear power plants many of the welds in austenitic tubes have to be inspected by means of ultrasonic techniques. If component-identical test pieces are available, they are used to qualify the ultrasonic test technology. Acoustic field measurements on such test blocks give information whether the beam of the ultrasonic transducer reaches all critical parts of the weld region and which transducer type is best suited. Acoustic fields have been measured at a bimetallic, a V-shaped and a narrow gap weld in test pieces of wall thickness 33, 25 and 17 mm, respectively. Compression wave transducers 45, 60 and 70° and 45° shear wave transducers have been included in the investigation. The results are presented: (1) as acoustic C-scans for one definite probe position, (2) as series of C-scans for the probe moving on a track perpendicular to the weld, (3) as scan along the weld and (4) as effective beam profile. The influence of the scanning electrodynamic probe is also discussed.     

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.     

Monitoring the filling level of the rpv using stationary emus-probes

The determination of the filling level and the initiation of growth of bubbles in vessels and pipes containing fluids is an essential component of monitoring during operation.The ultrasonic pulse-echo-method is a measuring procedure suited for this purpose and applicable from the outside. Piezoelectric ultrasonic transducers can be used in principle at a temperature of 300°C, but in practice these transducers are not preferred because of the expense and inconvenience in coupling them to the vessel wall.These problems are solved using lectro agnetic- ltrasonic-(EMUS-)transducers. Due to physical reasons a longitudinal wave is generated in the fluid by the refraction of a shear wave in the vessel-wall. The filling level is measured in a pitch and catch-technique by a mirror reflection of the longitudinal wave at a construction element inside the vessel. This paper reports on laboratory investigations concerning the applicability of the technique and first experiences with an EMUS-prototype system installed in a nuclear power plant.     

Development of an ultra sonic phased array system for nondestructive tests of nuclear power plant components

A phased array ultrasonic inspection (PAULI) system is being developed to obtain electronically scanned ultrasonic images of the inside of nuclear power plant components for nondestructive evaluation. The development strategy of PAULI system was the modification of a medical ultrasound imaging system that had 64 individual transceiver channels. Optimization of array transducers has been also pursued based on the systematic investigation of the radiation beam field simulated by the use of the boundary diffraction wave models. 7.5 MHz phased array transducers was, then, fabricated and tested with the carbon steel specimen having side-drilled holes. For the nondestructive tests on power plant component, a sample mockup of turbine blade root with EDM notches was fabricated and the detection capability was demonstrated. The developed system can provide electronically scanned ultrasonic images in real time fashion and greatly enhance the efficiency and reliability in the flaw detection and location in comparison with the classical ultrasonic testing (UT) using A-scan signals. For the flaw classification, the analysis of the electronically scanned ultrasonic images was not sufficient at this moment but analysis of features obtained from A-scan signals of flaws at the various steering angles showed the potential capability.     

An online monitor ionization chamber used in particle therapy

The clinical trials of tumor therapy using heavy ions beam 12C are now in progress at Institute of Modern Physics in Lanzhou. In order to achieve the precise radiotherapy with the high energy 12C beam in active pencil beam scanning mode, we have developed an ionization chamber(IC) as an online monitor for beam intensity and also a do-simeter after calibration. Through the choosing of working gas and voltage, optimizing of the electrics and the read-out system, calibrating the linearity, the detector system provide us one of the simple and highly reliable way to monitoring the beam during the active pencil beam scanning treatments. The measurement results of this detector sys-tem show that it could work well under the condition of high energy 12C beam in active pencil beam scanning mode.     

常波长和飞行时间模式下中子散射的散射矢量分辨率分析

讨论了中子散射实验中散射矢量分辨率问题，并根据目前谱仪通常的角度分辨和波长分辨参数，给出了常波长模式和飞行时间模式的分辨率曲线，并比较了不同模式的优缺点。分析表明，对于低q范围（〈0．4nm^-1）散射实验测量，飞行时间模式的分辨率更好；对于高q范围的中子散射测量，常波长模式更适合。     

Performance of the Sumy nuclear microprobe with the integrated probe-forming system

The integrated probe-forming system for the Sumy nuclear microprobe comprises two doublets of magnetic quadrupole lenses of new design. Each doublet has been made from a single piece of soft iron by electro-discharge machining. This paper describes the performance tests of the microprobe including the beam scanning control and data acquisition systems. In the first runs a spot size of about 2 μm (FWHM) was obtained for the high beam current mode (up to 200 pA) by scanning a conventional copper grid with 1000 meshes per inch. Simulated beam optics parameters are compared with the experimental data.     

Inspection procedure assessment using modelling capabilities

Before carrying out inspections on technical components, criteria have to be met to qualify the inspection procedure. The inspection qualification can be performed by technical justification or performance demonstration. The qualification of non-destructive testing methods can be checked on full scale mock-ups where real or realistic defects are implemented. To minimize costs it will become mandatory to model the inspection procedure. In the case of ultrasonic testing, the modelling includes the ultrasonic probe, the pulse-defect interaction and the probe geometry. The applied modelling code is the elastodynamic finite integration technique (EFIT) which includes mode conversion effects. The results of the code are either wave fields, A-scans at different probe positions or complete r.f. data fields. Examples demonstrate the efficiency in modelling angle beam probes which transmit both pressure, shear and subsurface longitudinal waves. These waves are scattered by horizontal or surface breaking cracks. The modelled r.f. data fields are used within the synthetic aperture focusing approach to predict the ultrasonic image which would be obtained in performing the experiment. In addition it will be shown that the EFIT wave fronts for anisotropic homogeneous media are explicitly related to the group velocity in these media.     

First direct-write lithography results on the Guelph high resolution proton microprobe

The recently completed high-resolution proton microprobe at the University of Guelph is Canada’s first one-micron nuclear microprobe, which represents the country’s state-of-the-art technology for various nuclear microprobe applications, e.g. direct-write microlithography. Its probe-forming system is comprised of a triplet Oxford Micro beams magnetic quadrupole lenses, along with high-precision objective slits. High energy protons coming off a 3 MV particle accelerator can achieve a nominal resolution of one micro and a beam current of several hundred of picoamperes when arriving at the target. This proton probe is ideal for the use of direct-write lithography with the incorporation of a magnetic scanning system and motorized sample stage.Preliminary lithography results have been obtained using spin-coated PMMA photoresist as specimen. The beam spot size, beam range and straggling inside the substrate and the exposure conditions are investigated by using scanning electron microscopy. This facility is the first in Canada to perform focused direct-write ion beam lithography, which is ideal for modification and machining of polymer and semiconductor materials for biological, microfluidic and ultimate lab-on-chip applications.     

蒸汽发生器换热管电磁超声纵向导波换能器设计与优化

高温气冷堆蒸汽发生器换热管特殊的螺旋结构导致传统外置型电磁超声导波换能器难以进行有效检测。本文针对蒸汽发生器不锈钢换热管的缺陷检测,开发了一种新型内置型电磁超声纵向导波换能器,建立了有限元多物理场耦合模型,研究了换能器铁磁结构的静态磁场分布,并对换能器激励出的纵向导波进行了时域仿真。结果表明：采用挤压聚磁的换能器结构可保证线圈附近的垂直方向磁场远大于水平方向磁场,能高效地在管道内部激励单一模式的纵向导波;优化后的探头可检测直径为5 mm的通孔缺陷和长×宽×深为20 mm×1.5 mm×1.2 mm的环向槽缺陷。因此,新型电磁超声纵向导波换能器可有效激励纵向导波,并有望应用于高温气冷堆蒸汽发生器换热管的在役缺陷检测。     

小型静态CT用多焦点X射线源电子束偏转系统研究

第5代全静态电子束CT（EBCT）能在被检测物体、射线源和探测器均处于静止状态下完成CT扫描成像。这种EBCT成像方式既可应用于粉体材料、生物活体样品等易形变物体的CT检测,又可应用于物流包裹、在役管线等的快速CT检测。高精度的电子束偏转系统是静态CT成像多焦点射线源的关键技术之一。本文基于麦克斯韦电磁场相互作用理论,探讨了电子束在均匀磁场、小偏转角、近轴区域内的散焦、畸变及灵敏度特性,研究了影响电子束扫描系统焦点位置重复精度的物理参数及电子束在靶平面上的扫描偏转量与偏转线圈电流的线性关系。并设计、加工制作了一种小型高精度多焦点X射线的电子束偏转扫描系统,实验采用直径0.1 mm标准针规电子束扫描DR投影图像序列,验证了电子束偏转系统有良好的偏转线性,偏转量正比于O点的磁场强度,而与电子束的位置等初始条件无关。实验通过电子束偏转系统控制电子束偏转扫描,获得了熔断式保险管（Ø100 μm）的250个 X 射线视角投影,完成了第5代全静态三维CT重建图像。     

Ray Tracing for Doppler Backscattering System in the Experimental Advanced Superconducting Tokamak

The Doppler backscattering system has been widely used for turbulence measurements,and the microwave beam will be backscattered near the cut-off layer when the Brag condition is fulfilled.In tokamak,the ray-tracing code is used to obtain the radial position and perpendicular wave number of the scattering layer for turbulence velocity measurement and the WKB(Wentzel-Kramers-Brillouin) approximation should be satisfied for optical propagation.To calculate the backscattering location and wave number at the cut-off layer only,a single ray tracing in the cross section is enough,while for spatial and wave number resolution calculation,multiple rays reflecting the microwave beam size should be used.Considering the angle between the wave vector and the magnetic field,a three-dimension quasi-optical Gaussian ray tracing is sometimes needed.     

大型集装箱检测系统管理站的任务需求分析与结构规划

由加速器周期性产生的Ｘ射线经前准直器成形为扇形脉冲束流，透过集装箱后再经过后准直器进入阵列探测器，再由前置放大器放大成形为电压信号送入采样保持电路，经多路选择器送去变换成为一组数字量，再经过一系列的预处理就可形成一列象素。由于集装箱是载于拖动装置上的，随着拖动装置的运动，这一列列的象素就可组成一幅完整的集装箱透视图，这样的一个完整过程由中心管理站统一控制和同步。本文介绍实时扫描数据获取与处理，并给     

Polarization and Mode Control of EAST 140 GHz ECRH&CD System

The 140 GHz electron cyclotron heating and current drive (ECRH&CD) project was launched in 2011 on EAST tokamak facility, which is designed to launch 4 MW of total power for the duration up to 1,000 s into the plasma. The heating and current drive efficiencies depend on the wave coupling mode in plasma and the coupling performance relies on polarization characteristics of injected beam, so polarization control is necessary for efficient plasma heating and current drive. Two polarizer miter bends will be used to control the wave polarization for each transmission line on EAST ECRH&CD system, any required wave polarization can be produced by adjusting the mirror rotation angle of each polarizer miter bend. This work mainly shows the calculated polarizer mirror settings as a function of the injection angles for pure second extraordinary harmonic mode coupling.     

在线同位素分离器监控系统的研制

在线同位素分离器(ISOL)装置是HI-13串列加速器升级工程中产生放射性核束及13 MeV串列加速器的注入部分,其能产生多种放射性核束,具有高质量分辨率的特点。为实现该装置的监控任务,结合ISOL的分布情况和特点,设计了一套PLC框架下构建的基于以太网的分布式控制系统。本文介绍受控设备的特点、控制方式、监控系统的基本结构、安全联锁和抗干扰设计、图形化监控软件设计、数据存储方式及运行情况。     

扫描探针电子能谱仪控制系统的研制

报道了自行搭建的扫描探针电子能谱仪(SPEES)控制系统的硬件及软件实现.该系统包括探针三维扫描控制、谱仪通过能电压扫描控制及样品电流反馈控制,在针尖控制上能够实现x、y、z三个方向上的定位以及恒高模式与恒流模式的扫描,在电子能谱测量上能够实现能量定点模式和能量扫描模式.对石墨表面Ag岛及石墨表面Au纳米结构的SPEE...     

合肥光源注入过程中束流负载效应和束流强度限制

根据储存环高频系统束流负载理论，研究计算了合肥光源注入过程中高频系统的大失谐角工作模式和调谐工作模式。综合考虑两种模式利弊，给出了更为灵活的注入模式。对于合肥光源，只要新高频系统参数设置合理，束流可顺利注入积累到设计值300mA以上。