微脉冲电子枪的动力学研究

 利用SEEG程序模拟计算了微脉冲电子枪束流动力学问题。在不考虑空间电荷效应的情况下，模拟了在微脉冲电子枪中电子纵向聚束的过程。进而详细研究了在空间电荷效应作用及相聚过程共同作用下形成饱和电流的过程。在此基础上，给出了经过优化后的微脉冲电子枪腔型特性,使用SEEG程序对该枪进行束流动力学模拟计算。最后给出一个实验用微脉冲电子枪的物理设计。     

DNA microarray scanner with a DVD pick-up head

A low-cost highly sensitive DNA microarray scanner for fluorescent detection is developed based on the pick-up head of a commercially available optical storage device, DVD. A laser beam of 650 nm, generated by a DVD laser diode, is used for dynamic auto-focusing as well as the excitation of Cy5 fluorescent dye. The fluorescence intensity emitted from Cy5 dye is measured by a photomultiplier tube (PMT). In contrast to other microarray scanners, the DVD-based scanner offers the auto-focusing function using the focus error signal (FES) and a voice coil motor (VCM), and this enables fast response, high accuracy and compact size. The fluorescence-detecting performance of the scanner is inspected by using a commercial BAC (bacterial artificial chromosome) oligonucleotide chip and a scanner evaluation microarray (DS01). Experiments have shown that the DVD-based scanner meets the limit of detection, ensuring the feasibility of a low-cost, highly sensitive DNA microarray scanner.     

Beam distribution reconstruction simulation for electron beam probe

An electron beam probe(EBP) is a detector which makes use of a low-intensity and low-energy electron beam to measure the transverse profile, bunch shape, beam neutralization and beam wake field of an intense beam with small dimensions. While it can be applied to many aspects, we limit our analysis to beam distribution reconstruction.This kind of detector is almost non-interceptive for all of the beam and does not disturb the machine environment.In this paper, we present the theoretical aspects behind this technique for beam distribution measurement and some simulation results of the detector involved. First, a method to obtain a parallel electron beam is introduced and a simulation code is developed. An EBP as a profile monitor for dense beams is then simulated using the fast scan method for various target beam profiles, including KV distribution, waterbag distribution, parabolic distribution,Gaussian distribution and halo distribution. Profile reconstruction from the deflected electron beam trajectory is implemented and compared with the actual profile, and the expected agreement is achieved. Furthermore, as well as fast scan, a slow scan, i.e. step-by-step scan, is considered, which lowers the requirement for hardware, i.e. Radio Frequency deflector. We calculate the three-dimensional electric field of a Gaussian distribution and simulate the electron motion in this field. In addition, a fast scan along the target beam direction and slow scan across the beam are also presented, and can provide a measurement of longitudinal distribution as well as transverse profile simultaneously. As an example, simulation results for the China Accelerator Driven Sub-critical System(CADS) and High Intensity Heavy Ion Accelerator Facility(HIAF) are given. Finally, a potential system design for an EBP is described.     

Beam foil electron spectroscopy near the forward direction

We report measurements of angular distributions of the integrated yields and energy distributions of electrons having velocities near the ion velocity for 0.75, 1 and 2 MeV ³He II incident on amorphous carbon foils of 10, 20 and 50 μg/cm².     

微脉冲电子枪的动力学研究

利用SEEG程序模拟计算了微脉冲电子枪束流动力学问题。在不考虑空间电荷效应的情况下,模拟了在微脉冲电子枪中电子纵向聚束的过程。进而详细研究了在空间电荷效应作用及相聚过程共同作用下形成饱和电流的过程。在此基础上,给出了经过优化后的微脉冲电子枪腔型特性,使用SEEG程序对该枪进行束流动力学模拟计算。最后给出一个实验用微脉冲电子枪的物理设计。     

Proton pick-up from Mo

The reaction ⁹²Mo(t, α)⁹¹Nb has been carried out at a triton bombarding energy of 12 MeV. Angular distributions of the emitted α-particles were obtained and compared with DWBA predictions. Relative spectroscopic factors were obtained for six low-lying states and are discussed with reference to shell-model calculations.     

负氢潘宁型离子源的束流引出测量

在中国工程物理研究院流体物理研究所自行研制的负氢潘宁型离子源上进行负氢束流引出测量实验,采用单电极、双电极、三电极束流引出测量方法进行初步束流引出测量,束流强度的实验测量结果远远高于空间限制流的理论计算值。因此,提出一种电屏蔽盒的直流束流引出测量方法。阐述了电屏蔽盒直流束流引出测量的基本方法、束流轨迹的CST数值模拟以及束流引出测量实验结果。研究表明:引出电压为2 kV,引出间隙为3 mm,磁感应强度为0.435 T时,得到较为精确的负氢束流引出强度约100 A。通过空间电荷限制流的V3/2定律进行拟合,推算得到引出电压为40 kV时,负氢束流强度约达到4 mA。     

强流电子束引出窗风冷数值模拟

 研究了1.2 MW大功率电子加速器引出窗钛膜受力状况,确定其工作温度必须控制在150 ℃以内。此温度下,热传导和热辐射的散热作用可以忽略,强迫风冷是唯一的散热途径。用流体模拟计算软件分析了钛膜冷却效果与出口风速和距离之间的关系,分析回流区的存在及其影响,并对引出窗结构做了初步优化。模拟了附加隔离窗形成的封闭空间对引出窗风冷的影响,模拟结果为：提出的非均布扫描方式可以将引出窗输出能力提升76%。     

Beam rotation and shear in a large electron beam diode

The time-averaged electron-beam current distribution of one of the electron guns of the large Aperture Module (LAM) of the Aurora laser was measured as part of a larger set of experiments designed to study the electron beam transport to and energy deposition in the LAM laser chamber. The radiograms made on the center line of the LAM laser chamber while the laser chamber was at vacuum pressure demonstrated several of the expected results. The beam was relatively uniform over the aperture, with the exception of shadows cast by the diode anode wires, the Hibachi ribs, and the Hibachi support structure. At a depth of 50 cm into the laser chamber, the self-magnetic field of the beam produced a shear in the top and bottom edges of 15 cm. At the same depth the applied magnetic field caused a rotation of the entire beam profile of about 3°     

不同磁路电子回旋共振离子源引出实验

空间推进所用的电子回旋共振离子源(ECRIS)应具有体积小、效率高的特点. 本文研究的ECRIS使用永磁体环产生磁场, 有效减小了体积, 该离子源利用微波在磁场中加热电子, 电子与中性气体发生电离碰撞产生等离子体. 磁场在微波加热电子的过程中起关键作用, 同时影响离子源内等离子体的约束和输运. 通过比较四种磁路结构离子源的离子电流引出特性来研究磁场对10 cm ECRIS性能的影响. 实验发现: 在使用氩气的条件下, 特定结构的离子源可引出160 mA的离子电流, 最高推进剂利用率达60%, 最小放电损耗为120 W·A^-1; 所有离子源均存在多个工作状态, 工作状态在微波功率、气体流量、引出电压变化时会发生突变. 离子源发生状态突变时的微波功率、气体流量的大小与离子源内磁体的位置有关. 通过比较不同离子源的引出离子束流、放电损耗、气体利用率、工作稳定性的差异, 归纳了磁场结构对此种ECRIS引出特性的影响规律, 分析了其中的机理. 实验结果表明: 保持输入微波功率、气体流量、引出电压不变时, 增大共振区的范围、减小共振区到栅极的距离, 离子源能引出更大的离子电流; 减小共振区到微波功率入口、气体入口的距离能降低维持离子源高状态所需的最小微波功率和最小气体流量, 提高气体利用率, 但会导致放电损耗增大. 研究结果有助于深化对此类离子源工作过程的认识, 为其设计和性能优化提供参考.     

一种边缘提取的图像分割方法

图像分析技术从广义上来讲 ,是指从图像中提取有用的数据或其它信息。图像分割是图像分析技术的重要手段 ,在前人的理论基础上经过实验提出了一种边缘提取的图像分割方法———行扫描空间带通滤波法。该方法在电视图像的自动跟踪识别中取得了很好的效果 ,是一种较为可取的图像分割方法     

Beam lifetime measurement and analysis in Indus-2 electron storage ring

In this paper, the beam lifetime measurement and its theoretical analysis are presented using measured vacuum pressure and applied radio frequency (RF) cavity voltage in Indus-2 electron storage ring at 2 GeV beam energy. Experimental studies of the effect of RF cavity voltage and bunched beam filling pattern on beam lifetime are also presented. An equation of stable beam current decay is evolved and this equation closely follows the observed beam current decay pattern. It shows that the beam is stable and the beam current decay is due to the beam–residual gas interaction (vacuum lifetime) and electron–electron interaction within a bunch (Touschek lifetime). The estimated vacuum, Touschek and total beam lifetimes from analytical formulations are also compared with the measured beam lifetime.     

Beam damage by the induced electric field in transmission electron microscopy

Electric fields can be induced by electron irradiation of insulating thin film materials. In this work, the electric fields under a broad beam illumination in transmission electron microscopy (TEM) are analyzed for insulating samples. Some damage phenomena observed can be interpreted by the mechanism of damage by the induced electric field (DIEF). For broad-beam illumination in an ultra-thin specimen, the electric field near the center of the illumination may not be strong, but at the periphery of the illumination the electric field can be significant. Therefore, damage may be easily observed in these regions rather than at the center of the illumination. For a beam which is broad compared to the specimen thickness, e.g. 100 ∼ 1000 nm, a strong electric field pointing inward into the specimen near the surface region may result in cation diffusion into the specimen and/or anion diffusion out to the surface region. Meanwhile, a strong electric field perpendicular to the beam direction near the edge of the illumination may attract anions into the illuminated region, but eject cations to the periphery. For a wedge-shaped specimen, the electric field points inward into thicker region, driving cations toward the thicker region, while attracting anions to the edge region. On the sharp edge, a strong electric field pointing outward may be responsible for the edge-smoothing effect observed in insulating materials.     

Beam deceleration for block-face scanning electron microscopy of embedded biological tissue

The beam deceleration (BD) method for scanning electron microscopes (SEM) also referred to as "retarding" was applied to back-scattered electron (BSE) imaging of the flat block face of a resin embedded biological specimen under low accelerating voltage and low beam current conditions. BSE imaging was performed with 0-4 kV of BD on en bloc stained rat hepatocyte. BD drastically enhanced the compositional contrast of the specimen and also improved the resolution at low landing energy levels (1.5-3 keV) and a low beam current (10 pA). These effects also functioned in long working distance observation, however, stage tilting caused uncorrectable astigmatism in BD observation. Stage tilting is mechanically required for a FIB/SEM, so we designed a novel specimen holder to minimize the unfavorable tilting effect. The FIB/SEM 3D reconstruction using the new holder showed a reasonable contrast and resolution high enough to analyze individual cell organelles and also the mitochondrial cristae structures (~5 nm) of the hepatocyte. These results indicate the advantages of BD for block face imaging of biological materials such as cells and tissues under low-voltage and low beam current conditions.     

强流电子束引出窗风冷数值模拟

研究了1.2 MW大功率电子加速器引出窗钛膜受力状况,确定其工作温度必须控制在150 ℃以内。此温度下,热传导和热辐射的散热作用可以忽略,强迫风冷是唯一的散热途径。用流体模拟计算软件分析了钛膜冷却效果与出口风速和距离之间的关系,分析回流区的存在及其影响,并对引出窗结构做了初步优化。模拟了附加隔离窗形成的封闭空间对引出窗风冷的影响,模拟结果为：提出的非均布扫描方式可以将引出窗输出能力提升76%。     

Effect of electron and optical factors on the beam extraction coefficient of large-area electron accelerators

A combined numerical-analytical model for the electron-optical system of a large-area accelerator is suggested. The model is used to analyze various electron and optical factors that affect the beam extraction coefficient. To find ways of improving the beam extraction coefficient, the spatial and angular characteristics of the beam are calculated in various cross sections. The effect of the magnetic field produced by the cathode filament current is studied in detail for the first time.     

不同磁路下微型ECR中和器电子引出的模拟研究

电子回旋共振(ECR)中和器是微型ECR离子推力器的重要组成部分,其引出的电子用于中和ECR离子源的离子束流,避免了航天器表面电荷堆积,并且电子引出性能对推力器的整体性能起着重要作用.为了分析影响微型ECR中和器电子引出的因素,本文建立了二维轴对称PIC/MCC计算模型,通过数值模拟研究不同磁路结构对中和器的电子引出,及不同腔体长度对壁面电流损失的影响.计算结果表明, ECR区位置和引出孔附近磁场构型对中和器的电子引出性能至关重要.当ECR区位于天线上游,电子在迁移扩散中易损失,并且电子跨过引出孔前电势阱所需的能量更高.如果更多磁力线平行通过引出孔,中和器引出相同电子电流所需电压较小.当ECR区被天线切割或位于下游时,电子更易沿磁力线迁移到引出孔附近,从而降低了收集板电压.研究了同一磁路结构下不同腔体长度对电子引出的影响,发现增加腔体长度,使得更多平行轴线的磁力线通过引出孔从而避免电子损失在引出板表面,增加了引出电子电流.研究结果有助于设计合理的中和器磁路和腔体尺寸.     

Beam electron energy distribution at a volume nanosecond discharge in atmospheric-pressure air

The energy distributions of beam electrons and x-ray photons in a volume nanosecond discharge on atmospheric-pressure air are studied. Several groups of elevated-energy electrons are found. It is shown that electrons with an energy from several tens to several hundreds of kiloelectronvolts (which is lower than a maximal voltage across the gap) make a major contribution to the beam current measured behind thin foils. It is corroborated that fast electrons (with an energy from several kiloelectronvolts to several tens of kiloelectron-volts) arise 100–150 ps before the basic peak of the beam current, elongating the current pulse and significantly increasing its amplitude. The contribution from electrons with an anomalously high energy (exceeding a maximal voltage across the gap) to the beam current is shown to be insignificant (less than 5%). The x-ray spectra in gas-filled diodes of different design are studied. Techniques of measuring the subnanosecond electron beam current and mechanisms generating fast and runaway electrons in volume high-pressure gas discharges are analyzed.