Terahertz radiation from interaction between an electron beam and a planar surface plasmon structure

The possibility of an electron beam exciting surface plasmons in conducting metal is discussed in this paper. A planar perfect-structure with subwavelength holes is proposed. The phenomenon that mimicking surface plasmon waves can be excited and amplified by an electron beam is proved theoretically and numerically. The mechanism of transmission through a subwavelength hole array is exploited to enhance the interaction between the electron beam and the mimicking surface plasmons.     

Focused electron beam induced deposition as a tool to create electron vortices

Focused electron beam induced deposition (FEBID) is a microscopic technique that allows geometrically controlled material deposition with very high spatial resolution. This technique was used to create a spiral aperture capable of generating electron vortex beams in a transmission electron microscope (TEM). The vortex was then fully characterized using different TEM techniques, estimating the average orbital angular momentum to be ∼0.8ℏ per electron with almost 60% of the beam ending up in the ℓ = 1 state.     

用于测量强流脉冲电子束的B-dot

 描述了B-dot探头测量脉冲电子束流强度和束质心位置的原理,分析了B-dot探头工作于自积分和微分模式的条件,并根据所测电子束流信号的前沿和脉冲宽度特点,确定B-dot探头工作于微分模式,设计其电感参数约为60 nH。在电子束流模拟装置上对B-dot探头的灵敏度系数和偏心曲线进行了标定,标定得到B-dot探头及测试线路的灵敏度系数为4 147 A/V。将探测器安装在神龙一号加速器上进行束测实验,多次实验结果表明该探测器可以实现电子束流强度和质心位置的准确测量。     

电子束空间极限电流的非线性理论研究

从电子束一维稳态传输的电势非线性Poisson方程出发,推导了圆柱波导内实心束和环形束空间极限电流与电子入射电势的依赖关系,给出了数值求解方法和解的特征,分析比较了数值计算与现有解析公式及粒子模拟的结果.考虑电子的横向运动,对数值方法进行了二维修正,计算结果与粒子模拟结果具有很好的一致性.说明利用数值方法计算电子电势非线性微分方程能够得到更精确的电子束在圆柱波导内的空间极限电流;另外,对其他形状的波导,尤其是难以得到解析式的情况,根据实际几何结构设置边界条件,数值方法可以方便地给出束流传输特性,对设计新型结构的高功率微波器件提供理论指导. 关键词： 相对论电子束 圆柱波导 空间极限电流 束流传输     

Radiation induced synthesis of gold/iron-oxide composite nanoparticles using high-energy electron beam

Composite nanoparticles consisting of gold and iron oxide were synthesized in aqueous solution systems by using a high-energy electron beam. The electron irradiation induces radiation-chemical reaction to form metallic gold nanoparticles. These gold nanoparticles were firmly immobilized on the surface of the support iron oxide nanoparticles. Surface of the support iron oxide nanoparticles are almost fully coated with fine gold nanoparticles. The size of these gold nanoparticles depended on the concentrations of gold ions, polymers and iron oxide nanoparticles in the solutions before the irradiation.     

A method for determining foil thicknesses in TEM by using convergent beam electron diffraction under weak beam conditions

In the present work, convergent beam electron diffraction was studied in zirconium (a material of intermediate atomic number) at 300 keV, under weak beam diffraction conditions. For a particular thickness, the details in an observed low order disc were matched to those calculated using the multibeam dynamical theory. This presents the possibility of determining foil thickness over a wide range, with an estimated experimental accuracy of ≈7% or less. In contrast to other convergent beam techniques, the present method, which uses weak beam conditions, can employ commonly-occurring low order reflections to extract thicknesses.

A simple equation based on the two beam approximation, is derived to determine foil thickness (to within ≈ 10%) without resorting to detailed image matching. This equation can be used for a rough estimate of foil thickness while carrying out TEM observations.     

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.     

Theoretical analysis of electron acoustic shock waves in magnetized superthermal plasma with electron beam

We have analysed the small-amplitude non-linear electron acoustic shock waves by taking into account the effects of electron beam in magnetized plasma. Satellite observations in different regions of the Earth's magnetosphere have shown that the electrostatic solitary waves are generally associated with electron or/and ion beams. The nonlinear Korteweg-de-Vries Burgers (KdVB) equation has been derived by considering the basic fluid equations and dissipation effects. The nonlinear coefficient of KdVB equation comes out to be negative. Only dip-shaped potential structures are reported here. For the parameters discussed in this paper, we did not find positive polarity shocks. This could be due to the restrictions on the plasma parameters since we are using the fixed densities of the cold, hot, and beam electrons as observed by the Viking satellite in the auroral region. In this paper, the importance of the cold electron to hot electron temperature in conjunction with the beam speed is pointed out. Increase in beam density, kinematic viscosity, and magnetic field results in increase in the amplitude while the increase in hot electron concentration and superthermality leads to decrease in potential. The numerical analysis is presented for the parameters corresponding to the observation of burst b event by Viking satellite in the dayside auroral zone of the earth's magnetosphere.     

带状电子束的空间电荷场

 利用理论分析和数值计算的方法研究了矩形波导内均匀电流密度的带状电子束模型的空间电荷场,给出了该带状电子束模型的空间电荷场的解析表达式,并研究了空间电荷场随带状电子束的几何参数和物理参数的变化规律。研究表明：在不改变电流密度的前提下,更宽的电子束可以传输更强的束流,而空间电荷场并不随束宽度的增大而增大,但是增加电子束厚度会使空间电荷场显著增强,从而不利于高流强电子束的传输;对于相同电流的带状电子束,保持电子束厚度不变,增大电子束宽度,相应地降低电流密度是降低空间电荷场的一个很好的途径,而保持电子束的宽度不变,增大束厚度,相应地降低电流密度只会使沿着电子束截面宽度方向的电场减小,而沿着电子束截面厚度方向的电场基本不变;对于相同电流和电流密度的带状电子束,更宽、更薄的电子束横截面尺寸能使沿着电子束截面宽度方向的电场降到更低,而沿着电子束截面厚度方向的电场只是略有减小。     

A novel approach for preparing silver nanoparticles under electron beam irradiation

Silver (Ag) nanoparticles were obtained when Ag microparticles were exposed to an electron beam in a transmission electron microscope (TEM). Results from TEM characterization indicated that the morphologies of the prepared Ag nanoparticles were quasi-circular, and the sizes were mainly in the range of 5–60 nm. The effect of irradiation time (t) on size and distribution of Ag nanoparticles was investigated. It was found that the sizes of Ag nanoparticles increased with the increase of t. The bigger Ag nanoparticles were near the Ag microparticle and the smaller ones were far from it. In addition, these Ag nanoparticles were monodisperse. This approach offered a new route for preparing Ag nanoparticles under electron beam irradiation, and the forming process of Ag nanoparticles was explained by the nucleation-growth mechanism.     

周期会切磁场聚焦强流相对论带状电子束的理论分析和粒子模拟

对低幅值、短周期、有偏置磁极的周期会切磁场中300 keV,3 kA带状电子束的传输进行了理论分析和粒子模拟。给出了将波导宽度考虑在内的轴向均匀带状电子束的空间电荷场和作用在有限厚度的带状电子束的短边和宽边上的聚焦力的表达式,并利用束匹配的方法得到了磁场的幅值和周期,以及电子束通道的宽度和高度等参数。最后根据理论计算的结果进行了3维粒子模拟验证,结果表明:束宽边上聚焦良好,而在短边上带状电子束的轴向有限长效应使得聚焦力与散焦力沿轴向不能完全匹配,在束包络上产生了Betatron振荡,但在300 mm的距离上传输效率仍能达到98%以上,说明有偏置磁极的周期会切磁场聚焦强流带状电子束在理论上是可行的。     

Wiggler磁场聚焦带状电子注

 带状电子注在螺线管磁场作用下传输时,易形成Diocotron不稳定性,导致电子注崩溃。采用Wiggler磁场聚焦带状电子注能防止Diocotron不稳定性。研究了Wiggler磁场聚焦带状注的作用机理,得出带状电子注在Wiggler场作用下的包络方程。结合理论分析,使用3维粒子模拟程序对带状电子注的Diocotron不稳定性和Wiggler磁场抑制不稳定性分别进行了模拟。研究表明:合适的选择磁场大小和周期能有效抑制Diocotron不稳定性,使得设计带状电子注行波管成为可能。     

HIRFL-CSR电子冷却系统空心电子束性能研究

 电子冷却系统中冷却力的大小与电子束的温度密切相关。由于强流电子束自身产生的空间电荷场,使得电子束的速度离散,增加了电子束温度,降低了冷却效率。为了减小空间电荷效应,HIRFL CSR的电子冷却系统将首次采用空心电子束对储存环中的重离子束流进行冷却。通过分析实心电子束和空心电子束的空间电荷场,研究了其对电子束速度和温度的影响。     

微波电子回旋共振等离子体阴极电子束的实验研究

介绍了实验室研制的微波电子回旋共振(ECR)等离子体阴极电子束系统及初步研究结果，该系统包括微波ECR 等离子体源、电子束引出极、聚焦线圈等。通过测量水冷靶电流和靶上的束斑尺寸，实验研究了微波ECR 等离子体阴极电子束的流强、聚束性能等随电子束系统工作条件的变化。结果表明：微波输入功率越高、引出电压越高，引出电子束流强越大；工作气压对电子束流强的影响较复杂，随气压增加呈现出先降低后升高的特点；在7×10⁻⁴Pa 的极低气压下电子束流强可达75mA，引出电压9kV；能量利用率可达0.6；调整聚焦线圈的驱动电流，电子束的束斑直径从20mm 减小到13mm，电子束流强未有明显变化。     

Surface modification of TA2 pure titanium by low energy high current pulsed electron beam treatments

Surface integrity changes of TA2 pure titanium including surface topography, microstructure and nanohardness distribution along surface layer were investigated by different techniques of low energy high current pulsed electron beam treatments (LEHCPEBTs). The surface topography was characterized by SEM. Moreover, the TEM observation and X-ray diffraction analysis were performed to reveal the surface modification mechanism of TA2 pure titanium by LEHCPEBTs. The surface roughness was modified by electron beam treatment and the polishing mechanism was analyzed by studying the cross section microstructure of electron beam treated specimens by SEM and TEM. The results show that the surface finish obtains good polishing quality and there is no phase transformation but the dislocations by LEHCPEBT. Furthermore, the nanohardness in the surface modified layer is improved. The remelt and fine-grain microstructure of surface layer caused by LEHCPEBTs are the main polishing mechanism and the reason of modification of surface topography and the increment in nanohardness is mainly due to the dislocations and fine grains in the modified layer induced by LEHCPEBT.     

赝火花脉冲电子束传输中束斑分析

通过赝火花强流脉冲电子束对酸敏变色片和单晶硅的轰击试验，结合束流自箍缩效应进行理论计算，对赝火花脉冲电子束传输中束斑的变形进行了研究与分析. 结果表明椭圆形轰击束斑是由通过旁路电容的瞬态电流产生的方位角磁场所引起的，并且提出了解决束斑变形的有效方法. 关键词： 脉冲电子束 赝火花放电 束斑 自箍缩效应     

TEM study of ion implanted GaAs after pulsed electron beam annealing

Abstract

(001) GaAs single crystals were implanted with 150 keV Cr⁺ ions using a dose of 5 × 10¹⁵ ions cm^?2. The amorphized surface layers were subjected to pulsed electron beam annealing at energy densities in the range 0–1.3 J cm^?2. A detailed TEM investigation of the damaged and annealed surface layer was conducted. These observations were correlated with backscattering results.     

Eccentricity of the electron beam in a gyrotron cavity

Dependence of the coupling of the electron beam and RF field in a gyrotron cavity on eccentricity of the electron beam is studied.     

100 keV回旋电子束参数测量

 利用电子束轰击快响应荧光屏获得电子束横截面图像的方法,对100 keV大回旋轨道空心电子束(Cusp电子束)在横截面上的束轮廓及电荷密度分布进行了测量,计算出回旋电子束半径、螺旋角等参数,并与相同条件下的计算机数值模拟结果进行了对比和分析。测量结果表明初始磁场强度从0.003 5 T增加到0008 2 T时,电子束的拉莫半径从3.2 mm增加到3.9 mm,螺旋角从0.7增加到1.0,满足使用此电子束的回旋行波放大器的调试需求。     

合肥光源逐圈束流位置监测系统中的定时系统

定时系统是合肥光源逐圈束流位置监测和相空间测量系统中的重要组成部分，其主要目的是为数据采集卡提供与环内电子束团同步的时钟信号。该系统包含高速ECL时钟成形、分频电路、程控延时电路、控制模块等部分。可实现延时范围0～220ns，最小延时步距0.5ns，调整精度0.1ns，时钟抖动小于200ps。系统控制软件基于客户/服务器结构，操作灵活、方便。