Computer simulation of the radiation of electrons axially channeled in a thin Ge single crystal

The radiation emitted by axially channeled electrons has been investigated by computer simulations. Using the Doyle-Turner approximation for the atomic scattering factor and taking thermal vibrations of the crystal atoms into account, two-dimensional continuous potentials for the 〈1 0 0〉 and 〈1 1 0〉 crystallographic axes of a thin Ge single crystal have been calculated. The trajectories, velocities and accelerations of channeled electrons are obtained by solving numerically the classical equations of motion in three dimensions. In the framework of classical electrodynamics, these data allow realistic simulations of spectral-angular distributions and energy spectra of axial channeling radiation as well.     

Tangential force and heating rate of a neutral relativistic particle mediated by equilibrium background radiation

A relativistic theory of fluctuation-electromagnetic interaction of a small neutral polarizable particle moving with respect to the equilibrium background radiation is developed. It is assumed that the particle radius is smaller then the characteristic wave length of the background radiation. General relativistic relations for the particle heating rate and tangential force are obtained and compared with the nonrelativistic and relativistic expressions of other authors.     

X-rays generated by relativistic electrons in a waveguide radiator mounted inside a betatron

We have observed X-ray emission from an X-ray waveguide radiator excited by relativistic electrons in the experiments carried out at Tomsk betatron B-35. A stratified radiator of a new type was mounted on a goniometer head inside the betatron toroid. The radiator consisted of the W-C-W layers placed on Si substrate. The photographs of the angular distributions of the radiation generated in the radiator by 20 and 33 MeV electrons showed the waveguide effect of the three-layer structure on X-rays generated in the radiator. The effect appeared in the angular distribution of the radiation as an additional peak attributed to guided X-rays inside a wide cone of usual Bremsstrahlung.     

Simulation of coherent spontaneous emission in a FEL with a groove guide

Based on a femtosecond linear accelerator, here we present a study of the use of a groove guide as the FEL interaction structure for high power FEL experiment. The transmission and attenuation characteristics of the dominant mode in the groove guide are discussed. And the coherent spontaneous emission in the FEL is simulated by Gover theory.     

Angular distribution of K-shell X-rays produced by 29 keV electrons incident on Ag

The absolute intensities of the Kα and Kβ X-rays produced by 29 keV electrons incident on a thick Ag target at forward angles in the range 0° to 55° relative to incident electrons have been measured. When corrections are made for attenuation within the target material, the results indicate that the K-shell X-rays are emitted isotropically. The experimental K-shell X-ray and bremsstrahlung production probability densities are compared to the results simulated by the Monte Carlo program, PENELOPE, and are found to be in good agreement.     

Coherent X-radiation of relativistic electrons in a single crystal under asymmetric reflection conditions

Coherent X-radiation of a relativistic electron crossing a single crystal plate with constant speed is considered in the two-wave approximation of the dynamic diffraction theory [Z. Pinsker, Dynamical Scattering of X-rays in Crystals, Springer, Berlin, 1984] in a Laue geometry. Analytical expressions describing the spectral-angular distribution of parametric X-radiation (PXR) and diffracted transition radiation (DTR) formed on a system of parallel atomic planes situated at an arbitrary angle δ to the surface of the crystal plate (asymmetric reflection) are derived. The dependences of the PXR and DTR spectral-angular density and their interference with angle δ are studied.     

Characteristics of coherent diffraction terahertz radiation at SDUV-FEL

1IntroductionTheterahertzradiationregimeoftheelectro-magneticwavespectrumisnotwellcoveredbyin-tensesourcesexceptforfewFELfacilities.Abright-nessfarexceedingthatfromablackbodyorsynchro-tronradiationsourcecanbeprovidedbyutilizingfemtosecondelectronbunches.Itcanbeusedforbasicandappliedresearchinmanyfields,suchasmaterialscience,high-Tcmaterials,polymerdynamicsandstructure,biologicalmolecules,phononandsurfacephysics,metrologystandards,etc.[1]Coherentdiffractionradiationisgeneratedbyrelativisticfe…     

Investigations on collective behavior in radiation process with random walk model

Coherent radiation, e.g. synchrotron radiation, transition radiation and diffraction radiation etc. are widely used for electron bunch length and longitudinal profile characterizations. Incoherent synchrotron radiation and transition radiation are usually used for beam’s transverse profile measurements. When the study for a whole bunch is to be performed, the collective behavior of electrons in the radiation process should be properly considered. In this paper, the collective behavior in radiation process is studied in detail with random walk model. It is found that the microscopic discreteness and randomness of electrons within the bunch plays a great role in the radiation process especially for the incoherent radiation component. Only when the discreteness and randomness of electrons is taken into account can the theoretical prediction for incoherent radiation intensity and angular distribution of a whole bunch coincide with experimental results. The results derived from random walk model are in good agreement with experimental results and show clearer physical picture in the radiation process.     

Charged particle propagation through nanostructures and associated radiation

In this report, using computer simulations, we investigate the channeling of high-energy charged particles in nanotube ropes and fullerites and estimate the capability of bent nanocrystals to deflect a particle beam. We also discuss electromagnetic radiation arising both from the non-uniform motion of the particles in the electrostatic potential of aligned atoms and from the transient polarization of the medium caused by the particles.     

基于有限元的同步辐射单色器一晶安装力学分析

双晶单色器是同步辐射光源光束线上的关键设备之一,其通过内部的第一晶体与第二晶体获得实验所需的单一波长的谱线,故晶体的装配安装直接影响实验站同步辐射光的品质。通过实验测试结合有限元分析的方法,建立单色器第一晶体在一定的螺栓紧固力下的有限元分析模型,验证模型的有效性,进而分析晶体的面形精度、安装机构的应力分布、"O"圈的形变等指标,研究安装过程中一晶及其安装机构的受力情况与力学响应,为高面形精度晶体的安装提供指导与借鉴。     

对于单个初电子在正比计数管中产生的脉冲高度分布形状的研究

研究单个初电子在正比计数管中产生的脉冲高度分布不仅对研究探测器本身有着重要意义,而且在其他方面也有许多重要应用。这项工作可以帮助我们了解正比计数管的探测机制,单纯研究充气正比计数管中气体放大倍数的涨落。 值得注意的是,这项工作最近几年又成为一种新发展起来的高灵敏检测技术——共振电离光谱技术与正比计数管结合起来检测单个原子的不可缺少的一部分。 一些研究者认为,单个初电子在正比计数管中产生的脉冲高度分布具有简单的指数衰减曲线的形状,另一些人的实验结果却表明单个电子的脉冲高度分布曲线具有峰结构。     

GaAs太阳电池1MeV电子辐射效应数值模拟

简要介绍了太阳电池的基本工作原理和辐射损伤机理。利用二维半导体器件数值模拟软件MEDICI,模拟计算了1MeV高能电子在辐射通量范围为1×1013～1×1015cm2时,对GaAs太阳电池主要输出参数(如开路电压Voc,短路电流Isc)的影响,并对计算结果进行了分析,计算结果与相关文献给出的实验数据吻合较好。     

Formation of spectral characteristics of channeling radiation from 800 to 2000 MeV electrons and positrons in a thin silicon crystal

The influence of the tails of particle trajectories on planar channeling radiation (CR) spectra from relativistic (800-2000 MeV) electrons and positrons in a thin silicon crystal is investigated. It is shown that the trajectory tails significantly change the CR spectra from electrons and positrons in specific parts of the spectra compared to calculations which do not take into account this effect.     

基于相干渡越辐射的束团长度测量研究

电子束团长度是束流诊断中的重要参数,基于相干渡越辐射(Coherent Transition Radiation,CTR)的测量方法是一种简单易行的高时间分辨率测量方法。本文调研并分析了不同电子束团长度测量方法的优缺点,选择基于CTR方法作为主要研究方向,主要针对上海深紫外自由电子激光实验装置(Shanghai Deep Ultra-Violet Free Electron Laser,SDUV-FEL)和X射线自由电子激光试验装置(Shanghai X-ray Free Electron Laser,SXFEL)进行了实验方案设计和模拟分析。结果表明,通过合理的参数选择和方案优化,用该方法可对飞秒至皮秒范围内的束团长度进行测量,时间分辨率能到达飞秒量级,满足SDUV-FEL的实验需求和SXFEL的工程需求。     

双晶单色仪第一晶体初安装姿态误差分析

双晶单色仪是同步辐射光束线中关键的光学部件,第一晶体的初安装姿态误差对双晶单色仪出射光方向影响复杂.通过建立同步辐射在第一晶体晶面上衍射的空间模型,得到了第一晶体的初安装姿态误差对出射光方向的影响关系式,并通过测定不同Bragg角时在荧光靶上的光斑的位置,得到确定第一晶体初安装投角、滚角、摆角误差的方法,可为第一晶体姿态调节装置提供数据.     

用同步辐射X射线荧光微区分析技术测定单晶硅中的掺杂元素As

利用同步辐射Ｘ射线微区分析技术，研究了单晶硅中掺杂元素Ａｓ浓度的定量分布，并对结果进行了讨论。     

Stoichiometry distribution of thin films deposited by laser ablation: Monte Carlo simulation

An expansion of a bi-component laser plume into a dilute background gas is simulated using a combined Monte Carlo simulation method. The effects of different types of collisions taking place during the transport of the ablated species on their distributions when arriving at a flat substrate are shown. Furthermore, we demonstrate that the film thickness distributions of both components and, hence, the final stoichiometry distribution, depend strongly on the incorporation probability of the species. This probability is expressed as a function of both deposited particle energy and the substrate absorbing properties. These studies can facilitate the comparison of the simulation results with experiments and are of particular interest for pulsed laser deposition (PLD) of multicomponent materials.