Non-Intrusive Magneto-Optic Detecting System for Investigations of Air Switching Arcs

In current investigations of electric arc plasmas, experiments based on modern testing technology play an important role. To enrich the testing methods and contribute to the understanding and grasping of the inherent mechanism of air switching arcs, in this paper, a nonintrusive detecting system is described that combines the magneto-optic imaging（MOI） technique with the solution to inverse electromagnetic problems. The detecting system works in a sequence of main steps as follows： MOI of the variation of the arc flux density over a plane, magnetic field information extracted from the magneto-optic（MO） images, arc current density distribution and spatial pattern reconstruction by inverting the resulting field data. Correspondingly, in the system, an MOI set-up is designed based on the Faraday effect and the polarization properties of light, and an intelligent inversion algorithm is proposed that involves simulated annealing（SA）.Experiments were carried out for high current（2 kA RMS） discharge cases in a typical low-voltage switchgear. The results show that the MO detection system possesses the advantages of visualization, high resolution and response, and electrical insulation, which provides a novel diagnostics tool for further studies of the arc.     

Image quality evaluation of linear plastic scintillating fiber array detector for X-ray imaging

It is important to assess image quality, in order to ensure that the imaging system is performing optimally and also identify the weak points in an imaging system. Three parameters mostly leading to image degradation are contrast, spatial resolution and noise. There is always a trade-off between spatial resolution and signal to noise ratio,but in scintillating fiber array detectors spatial resolution is not as important as signal to noise ratio, so we paid more attention to contrast and SNR of the system. By using GEANT4 Monte Carlo detector simulation toolkit, some effective parameters of the linear plastic scintillating fiber（PSF）array as an imaging detector were investigated. Finally we show that it is possible to use this kind of detector to take CT and DR (Digital Radiography) image under certain conditions.     

A complete implementation of list-mode reconstruction for PET

Tomography reconstruction algorithm is one of the key components of positron emission tomography (PET) scanners,most PET scanners use statistical iterative reconstruction algorithms from data in sinograms currently. However tomography reconstruction using list-mode data has many unique advantages,in recent years great attention has been paid to it,being in the process of rapid development and improvement.In this paper,using experimental data of small animal PET scanner Eplus-166,exploiting ordinary subsetized list-mode EM(S-LMEM) algorithm and orthogonal distance-based ray-tracer(OD-RT),we eventually achieve list-mode tomography reconstruction.System response matrix(SRM),which establishes mapping relationship between the image and the projection space,is one key problem in iterative reconstruction algorithm.OD-RT is based on an optimization Siddon’s algorithm to calculate the SRM,generating line-of-response(LOR) which is approximately Gaussian-shaped,achieving better modeling of detector response function(DRF).The results demonstrate that image resolution recovery achieves the inherent properties of the scanner and that on-the-fly ray-tracer for real-time calculation of system response matrix is feasible for dynamic reconstruction.Meanwhile,the optimal parameters for calculating SRM are found by experiments.     

Design of data transmission for a portable DAQ system

Field Programmable Gate Array （FPGA）, combined with ARM （Advanced RISC Machines） is increasingly employed in the portable data acquisition （DAQ） system for nuclear experiments to reduce the system volume and achieve powerful and multifunctional capacity. High-speed data transmission between FPGA and ARM is one of the most challenging issues for system implementation. In this paper, we propose a method to realize the high-speed data transmission by using the FPGA to acquire massive data from FEE （Front-end electronics） and send it to the ARM whilst the ARM to transmit the data to the remote computer through the TCP/IP protocol for later process. This paper mainly introduces the interface design of the high-speed transmission method between the FPGA and the ARM, the transmission logic of the FPGA, and the program design of the ARM. The theoretical research shows that the maximal transmission speed between the FPGA and the ARM through this way can reach 50 MB/s. In a realistic nuclear physics experiment, this portable DAQ system achieved 2.2 MB/s data acquisition speed.     

The development of data acquisition and processing application system for RF ion source

As the key ion source component of nuclear fusion auxiliary heating devices, the radio frequency(RF) ion source is developed and applied gradually to offer a source plasma with the advantages of ease of control and high reliability. In addition, it easily achieves long-pulse steady-state operation. During the process of the development and testing of the RF ion source, a lot of original experimental data will be generated. Therefore, it is necessary to develop a stable and reliable computer data acquisition and processing application system for realizing the functions of data acquisition, storage, access, and real-time monitoring. In this paper, the development of a data acquisition and processing application system for the RF ion source is presented. The hardware platform is based on the PXI system and the software is programmed on the Lab VIEW development environment. The key technologies that are used for the implementation of this software programming mainly include the long-pulse data acquisition technology, multithreading processing technology, transmission control communication protocol, and the Lempel–Ziv–Oberhumer data compression algorithm. Now, this design has been tested and applied on the RF ion source. The test results show that it can work reliably and steadily. With the help of this design, the stable plasma discharge data of the RF ion source are collected,stored, accessed, and monitored in real-time. It is shown that it has a very practical application significance for the RF experiments.     

A high-resolution small animal SPECT system developed at Tsinghua

An SPECT system dedicated to small animal imaging shall be of a millimeter spatial resolution or even better.This study was aimed at achieving 0.5-mm spatial resolution for a small animal SPECT system at low cost.It was developed from a single-head clinical SPECT scanner,with a seven-pinhole collimator and a four-degree-offreedom motion control stage.Several key techniques were developed,including high-resolution image reconstruction algorithm,high accuracy geometrical calibration method,and optimized system matrix derivation scheme.The system matrix was derived from Monte-Carlo simulation and de-noised by fitting each point spread function to a two dimensional Gaussian function.Experiments of point source and ultra micro hot rod phantom were conducted.With a spatial resolution of 0.5-0.6 mm,this system provides a practical way for low-cost high-resolution animal imaging on a clinic SPECT system.     

Development of Data Acquisition Card Driver for ICRH System on EAST

Presented in this paper is the development of the driver for the data acquisition card with a peripheral component interconnection （PCI） local bus on the ion cyclotron range of frequency heating （1CRH） system. The driver is mainly aimed at the embedded VxWorks system （real-time operating system） which is widely used in various fields of real-time systems. An efficient way is employed to develop this driver, which will advance the real-time control of the ICRH system on the experimental advanced superconductor tokamak （EAST）. The driver is designed using the TORNADO integrated development environment （IDE）, and implemented in C plus language. The details include the hardware configuration, analogue/digital （A/D） and digital/analogue （D/A） conversion, input and output （I/O） operation of the driver to support over five cards. The data acquisition card can be manipulated in a low-level program and meet the requirements of A/D conversion and D/A outputs.     

Determination of spatial resolution of plastic scintillation fiber array with a simple method

The spatial resolution of a position sensitive gamma-ray detector configuration based on plastic scintillation fiber array was measured using a Monte Carlo simulation method. Both point spread function and modulation transfer function （MTF） were presented. The factors that influence the spatial resolution were also discussed. The results of the simulation showed that the intrinsic spatial resolution was consistent with the size of the physical pixels and a few centimeters spatial resolution could be obtained under certain circumstances.     

An acquisition system of digital nuclear signal processing for the algorithm development

A principle and method of constructing the digital acquisition system is presented in this work, which is convenient for the study on the theories and algorithms of digital nuclear signal processing. The hardware system of the digital acquisition system consists of front-end controller, waveform digitizer and PC workstation, on which the software system has been developed based on Visual C＋＋ under Windows environment. The alterable-frequency sampling （AFS） algorithm and the alterable-frequency trapezoidal filter （AFTF） algorithm have also been studied in the real-time environment, along with a digital nuclear spectrum acquisition system being set up based on the new algorithms and the γ-ray spectra of 241Am being shown. A useful experimental platform could be provided by this work for the successive work such as the development of global digitized nuclear measurement system and the study of digital nuclear signal processing.     

Analysis and Performance of the Thomson Scattering Diagnostics on HT-7 Tokamak Based on I-EMCCD

A visible light imaging Thomson scattering （VIS-TVTS） diagnostic system has been developed for the measurement of plasma electron temperature on the HT-7 tokamak. The system contains a Nd：YAG laser （A = 532 nm, repetition rate 10 Hz, total pulse duration ≈ 10 ns, pulse energy 〉 1.0 J）, a grating spectrometer, an image intensifier （I.I.） lens coupled with an electron multiplying CCD （EMCCD） and a data acquisition and analysis system. In this paper, the measurement capability of the system is analyzed. In addition to the performance of the system, the capability of measuring plasma electron temperature has been proved. The profile of electron temperature is presented with a spatial resolution of about 0.96 cm （seven points） near the center of the plasma.     

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。     

箱包DR/SSCT检查系统图像重建算法研究

在箱包DR(DigitalRadiography)/CT安全检查系统基础上,开发了箱包DR/SSCT(singleslicespiralCT)检查系统,该系统可改善原系统检测客体耗时和漏检方面的缺点。研究工作分为更改数据采集系统和设计SSCT重建算法两部分,分别在模拟实验和物理实验中比较了各种SSCT重建算法的重建效果,并利用探测器数据插值提高重建图像质量。通过实验对照,本系统采用了360°LI(LinearInterpolation)和JH-HI(JiangHsieh-HalfscanInterpolation)加权重建算法。     

恒流模式直流流强检测系统的优化

介绍了上海光源恒流模式下直流流强检测系统的软硬件结构。Matlab仿真比对两种束流流强算法性能,结果表明,使用整数周期算术平均算法时,2 Hz系统带宽下系统直流流强测量分辨率可望好于0.38μA。由于Top-up模式束流的特性,对束流寿命算法进行优化,进行两点曲线拟合。介绍了Top-up模式下直流流强检测系统的置信度算法,并用实测数据进行了验证,数据预测准确,收敛速度快,性能较好。对DCCT系统的软件实现给出了软件流程图,指导软件代码的实现。     

Multi-pinhole SPECT Imaging with Silicon Strip Detectors

Silicon double-sided strip detectors offer outstanding instrinsic spatial resolution with reasonable detection efficiency for iodine-125 emissions. This spatial resolution allows for multiple-pinhole imaging at low magnification, minimizing the problem of multiplexing. We have conducted imaging studies using a prototype system that utilizes a detector of 300-micrometer thickness and 50-micrometer strip pitch together with a 23-pinhole collimator. These studies include an investigation of the synthetic-collimator imaging approach, which combines multiple-pinhole projections acquired at multiple magnifications to obtain tomographic reconstructions from limited-angle data using the ML-EM algorithm. Sub-millimeter spatial resolution was obtained, demonstrating the basic validity of this approach.     

Filter-based energy-resolved X-ray computed tomography with a clinical imager

Filter-based energy-resolved X-ray computed tomography (CT) is an approach for implementing energy-resolved CT imaging using a flat-panel-detector-based cone-beam system. In this study, we performed experiments with a 20-cm-diameter phantom on a clinical X-ray imager. The material density results showed good agreement with the ideal values. We also propose an improved method for obtaining the detector response function and the X-ray spectrum, which requires fewer measurements and will be practical for future clinical use. Issues such as scatter and image noise remain to be addressed.     

2D and 3D refraction-based visualization of breast cancer for early clinical check

Duetal carcinoma in-situ （DCIS） has been visualized by 2D XDFI （X-ray dark-field imaging） and further by a 3D X-ray CT, and the data was acquired by the X-ray optics DEI （diffraction-enhanced imaging）. A newly made al- gorithm was used for CT, Data of 900 projections with interval of 0.2 degrees were used. Ductus lactiferi, microcalci- fication in a 3D form have been clearly visible. The spatial resolution available was approximately 30 μm.     

Impedance imaging of two-phase flow field with mesh grouping method

There have been many attempts to measure the bubble distribution in two-phase flow fields and various techniques have been devised. However, the existing techniques require much improvement for imaging two-phase flow fields. In this study, the EIT (Electrical Impedance Tomography) technique is introduced for two-phase flow visualization. In the EIT, a static image reconstruction algorithm providing a higher spatial resolution is required. Using the conventional iterative static image reconstruction algorithms, however, the processing time increases rapidly with poor convergence characteristics as we try to obtain a higher spatial resolution. In order to overcome this problem, we propose an adaptive mesh grouping method utilizing the genetic algorithm and the fuzzy set theory. Computer simulations using the improved Newton–Raphson method with the proposed method show promising results indicating that we can significantly reduce the image reconstruction time without sacrificing spatial resolution.     

450keV锥束CT系统的散射校正研究

在450keV锥束工业CT成像系统中,对投影数据进行适当的散射校正是一步重要的数据校正.结合国内外散射校正方法研究的现状,对一种用散射校正板来进行散射校正方法的原理和实现进行了深入的研究.实验结果表明,这种校正方法能够对450KeV锥束CT成像系统进行有效地散射校正.