Experimental study on helium optical electron polarimetry

Optical electron polarimetry is suitable for calibration of a spin-polarized electron source, especially for measurement of polarization of spin-polarized electron beam. In this paper, a new optical electron polarimeter is described, which is based on the circularly polarized He radiation induced by the bombarding of He atoms with spin-polarized electrons. The theoretical basis of the optical electron polarimetry and the structure of the optical electron polarimeter are discussed. The measurement of polarization of spin-polarized electrons produced from a new GaAs （100） spin-polarized electron source is carried out. The result of polarization of 30.8% for our spin-polarized electron source is obtained using the He optical electron polarimeter.     

高入射能量下的金属二次电子发射模型

基于高入射能量电子产生二次电子发射的物理过程, 分别对高入射能量电子产生的真二次电子和背散射电子的概率进行理论分析与建模. 利用Bethe能量损失模型和内二次电子逸出概率分布, 推导出高入射能量电子产生有效真二次电子发射的系数与入射能量的关系式; 根据高入射能量电子在材料内部被吸收的规律, 推导出高入射能量电子产生背散射电子的系数与入射能量之间的关系式. 结合两者得到高入射能量下金属的二次电子发射模型. 利用该模型计算得到典型金属材料Au, Ag, Cu, Al的二次电子发射系数, 理论计算结果与采用Casino软件模拟金属内部散射过程得到的数值模拟结果相符. 关键词： 二次电子发射 高入射能量 金属表面 散射过程     

Electron dynamics and harmonics radiation due to electron oscillation driven by laser standing wave

The electron dynamics and harmonics radiation spectra due to electron oscillation driven by laser standing wave (SW) have been investigated considering a single electron mode. It is found that electron can pass through or be reflected from laser SW as electron is shot into laser SW from antinodes plane with initial velocity parallel to electric field of SW, and for electron incidence at arbitrary plane the attraction plane of electron trajectories will transfer from nodes plane to antinodes plane if initial electron kinetic energy exceeds a critical value. Further, the harmonics emission due to electron oscillation during passing through laser SW is considered in two cases of electron incidence plane at nodes and antinodes. In case of electron incidence at nodes, the spectrum of radiation is redshifted for backward radiation and blueshifted for forward radiation, and broadening of spectrum is noticed. These effects are much more pronounced at higher laser intensities. However, for case with electron incidence at antinodes, these phenomena vanish.     

磁控注入电子枪的研究

介绍了毫米波回旋速调管磁控注入电子枪的结构与特点.依据回旋管对电子枪的要求,考虑相对论效应和空间电荷效应,编制了一套计算程序.利用电子枪模拟程序对电子轨迹进行模拟计算,研究了电极形状、磁场分布以及电子轨迹与电子注参量的影响,为磁控注入电子枪的设计提供了理论依据. The Structure and characteristics of the magnetron injection gun (MIG) for mm wave gyro-klytron are introduced. According to the requirements for the gyro-klytron, the relativistic effect and the space charge effect is taken into account . A program is developed for CAD. An electron gun code is used to simulate the electron trajectory, the influence of electrode shape, magnet field, electron trajectory on the electron beam have been studied. The theory for design of the electron gun is presented.     

质子束团传输过程中的二次电子多级倍增

电子云不稳定性是强流质子加速器稳定运行的一个重大障碍。在电子云积累的过程中,二次电子多级倍增是电子云的主要来源。二次电子多级倍增机制可以用电子的运动和能量增益来分析。为了得到电子云的密度及分布,编写了一个模拟程序用来跟踪电子云的发展演化过程。分析了在质子束团作用下电子的运动,分析二次电子多级倍增的原因,并用模拟程序进行了计算,结果发现电子云与束团的纵向分布密切相关。     

Electron detachment from negative hydrogen and lithium ions by an ultrashort laser pulse

A model of electron detachment from negative ions is based on the approximation of instantaneous perturbation. A simple analytical representation for the ground state of the weakly bound electron is chosen to reproduce the radial distribution of electron density at any distance from the center of the ion. The probabilities of electron detachment from negative hydrogen and lithium ions are derived as functions of the transferred momentum of the laser field. The contribution of the inner shells of ions to the electron detachment is estimated. The momentum distribution of electrons in the final state is obtained. The effect of a pulse train on the total probability of detachment is considered for different pulse polarities. The conditions for the partial electron return to the initial state are revealed.     

Improved two-temperature model including electron density of states effects for Au during femtosecond laser pulses

The electron temperature dependences of the electron–phonon coupling factor and electron heat capacity based on the electron density of states are investigated for precious metal Au under femtosecond laser irradiation. The thermal excitation of d band electrons is found to result in large deviations from the commonly used approximations of linear temperature dependence of the electron heat capacity, and the constant electron–phonon coupling factor. Results of the simulations performed with the two-temperature model demonstrate that the electron–phonon relaxation time becomes short for high fluence laser for Au. The satisfactory agreement between our numerical results and experimental data of threshold fluence indicates that the electron temperature dependence of the thermophysical parameters accounting for the thermal excitation of d band electrons should not be neglected under the condition that electron temperature is higher than 10⁴ K.     

L波段强流单束团注入器的束流动力学计算

自由电子激光器要求高亮度、低能散度的电子束注入波荡器(Undulator)。本文叙述提供高亮度电子束的高频电子直线加速器中的注入器部分的设计计算。注入器由L波段(1300MHz)的十二分频和三分频两个谐振腔预聚束器和一个基波频率的变相速聚束器组成。粒子运动方程中考虑了空间电荷效应和束流负载效应。电子枪的注入参数:脉冲宽度T=4ns;电流I=5A;电子的初始动能E_0=100keV;电子束分布为高斯型。参数优化设计结果:单束团宽度小于25ps,峰值电流达400A以上,电子的平均归一化能量>4,束团内的能量差小于200keV。     

Spatial distribution of electron characteristic in argon rf glow discharges

The spatial distributions of the electron density and the mean electron energy of argon radio frequency (rf) glow discharge plasma in a plasma-enhanced chemical vapour deposition (PECVD) system have been investigated using an established movable Langmuir probe. The results indicate that in the axial direction the electron density tends to peak at midway between the two electrodes while the axial variation trend of mean electron energy is different from that of the electron density, the mean electron energy is high near the electrodes. And the mean electron energy near the cathode is much higher than that near the anode. This article focuses on the radial distribution of electron density and mean electron energy. A proposed theoretical model distribution agrees well with the experimental one: the electron density and the mean electron energy both increase from the centre of the glow to the edge of electrodes. This is useful for better understanding the discharge mechanism and searching for a better deposition condition to improve thin film quality.     

The tube character of electron drift in condensed inert gases

The behavior of an excess electron in condensed inert gases in an external electric field is considered at densities and temperatures at which the mobility of a slow electron is relatively high. On the basis of experimental data and a model of a pair electron interaction with atoms, an effective potential energy surface is constructed for an excess electron inside a dense inert gas. The region available for a slow electron consists of many intersecting channels that form a Delaunay network located between atoms. A drifting electron, as a quantum object, propagates along these channels (tubes), and electron transition between intersecting potential energy tubes of different directions provides an effective electron scattering. This mechanism of electron drift and scattering differs from that in gases and crystals. Peculiarities of electron drift inside dense inert gases are analyzed within the framework of this mechanism of electron scattering, leading to a moderate change of the electron mobility upon melting.     

电子清刷对微通道板增益及输出信噪比的影响

电子清刷是微通道板生产流程中常用的除气方法,会引起微通道板其他性能参量的变化.为研究电子清刷对微通道板输出信噪比及增益的影响,根据信噪比及增益的定义讨论了微通道板性能参量的测试方法,研制了微通道板参量测试系统.应用微通道板参量测试系统对微通道板进行了电子清刷处理,测试清刷过程中不同阶段微通道板的信噪比及增益变化.实验表明:微通道板增益随清刷时间增加而降低,同时增益稳定性提高;电子清刷过程中微通道板的输出信号及噪音的变化率与微通道板增益的变化率基本相同,输出信噪比基本不变.增益变化是影响清刷过程中信号及噪音变化的主要因素,并且电子清刷对微通道板输出信噪比影响较小.     

含负折射率介质的一维光子晶体构成的相干热辐射源的辐射特性及控制

电子清刷是微通道板生产流程中常用的除气方法,会引起微通道板其他性能参量的变化.为研究电子清刷对微通道板输出信噪比及增益的影响,根据信噪比及增益的定义讨论了微通道板性能参量的测试方法,研制了微通道板参量测试系统.应用微通道板参量测试系统对微通道板进行了电子清刷处理,测试清刷过程中不同阶段微通道板的信噪比及增益变化.实验表明:微通道板增益随清刷时间增加而降低,同时增益稳定性提高;电子清刷过程中微通道板的输出信号及噪音的变化率与微通道板增益的变化率基本相同,输出信噪比基本不变.增益变化是影响清刷过程中信号及噪音变化的主要因素,并且电子清刷对微通道板输出信噪比影响较小.     

An application of the electron mirror in the time-of-flight spectrometer

We suggest applying of the spherical electron mirror in the time-of-flight electron spectrometer with a position sensitive detector in order to increase the effective acceptance solid angle of the spectrometer. The spherical electron mirror is placed near the specimen and it focuses electrons on a position sensitive detector as a converging electron flux. The electron mirror increases the acceptance angle of the spectrometer by a factor of 20. The electron mirror of the spectrometer consists of an inner spherical electrode of the radius R and an outer spherical electrode of the radius 1.1R. The central segment of the inner electrode inside the linear angle of 80° is made of a grid. The detector plate radius is about 0.23R. The acceptance solid angle of the spectrometer with this electron mirror is about 1.1sr, the range of the polar angle of emission is 20°–90° relative to the surface normal, and the range of the azimuth angle of emission at its maximum is ±36° relative to the basic plane of the spectrometer. The design of the spectrometer allows to recover the electron trajectory for each detected electron and to calculate the energy and the emission angle of the electron. The energy resolution of the spectrometer is about 0.2 eV/ns for the electron energy of 10 eV. The energy range is from E_min0.1eU_r up to eU_r, where U_r is the retarding potential of the electron mirror. The perturbing influence of the grid of the electron mirror limits mainly the angular resolution of the spectrometer and affects relatively slightly the energy resolution. The electron spectrometer with two detectors and two electron mirrors symmetric about the spectrometer axis allows to measure electron pairs in coincidence in a wide range of emission angles and energies with k-resolutions.     

Natural geometric representation for electron local observables

An existence of the quartic identities for the electron local observables that define orthogonality relations for the 3D quantities quadratic in the electron observables is found. It is shown that the joint solution of the quartic and bilinear identities for the electron observables defines a unique natural representation of the observables. In the natural representation the vector type electron local observables have well-defined fixed positions with respect to a local 3D orthogonal reference frame. It is shown that the natural representation of the electron local observables can be defined in six different forms depending on a choice of the orthogonal unit vectors. The natural representation is used to determine the functional dependence of the electron wave functions on the local observables valid for any shape of the electron wave packet.     

二维电子体系在高密度下的稳定性

本文计算了高密度的二维电子体系的边缘能(将二维体系沿某一直线解离成两片时,形成单位长度新边缘所需要的能量)。结果发现,当r_ss^(c)(约0.415)时,边缘能变负,从而表明在高密度下,二维电子气的基态有可能发生不稳。我们分别讨论了二维非束缚的电子气和束缚的电子气基态的稳定性,并在一个简化的模型下给出了束缚的电子气基态稳定性的判据。 关键词：     

Processes in condensed inert gases involving excess electrons

Drift of an excess electron in dense and condensed inert gases in external electric field and excitation of atoms by electron impact in these systems are analyzed. The effective potential energy surface for an excess electron at a given electric field strength consists of wells and hills, and the actions of neighboring atoms are therefore separated by saddles of the potential energy. At such atomic densities that the difference of interaction potentials for an excess electron between neighboring wells and hills of the potential energy surface becomes small, the electron mobility is large. This is realized for heavy inert gases (Ar, Kr, Xe) with a negative scattering length of an electron on individual atoms. In these cases, the average potential energy of the electron interaction with atoms corresponds to attraction at low atomic densities and to repulsion at high densities. The transition from attraction to repulsion at moderate atomic densities leads to a maximum of the electron mobility. A gas model for electron drift in condensed inert gases is constructed on the basis of this character of interaction. Due to high electron mobility, condensed inert gases provide high efficiency of transformation of the electric field energy into the energy of emitting photons through drifting electrons. It is shown that, although the role of formation of autodetaching states in the course of electron drift is more important for condensed inert gases than for rare gases, this effect acts weakly on exciton production at optimal atomic densities. The parameters of a self-maintained electric discharge in condensed inert gases as a source of ultraviolet radiation are discussed from the standpoint of electron drift processes.     

Nonlocal electron kinetics in collisional gas discharge plasmas

Nonlocal phenomena in electron kinetics of collisional gas discharge plasmas, their kinetic treatment by a nonlocal approach, and relevant experimental results are reviewed in this paper. Using the traditional two-term approximation for the electron distribution function, a general method to analyze electron kinetics in nonuniform plasmas in DC and RF fields for atomic gases is presented for the nonlocal case, when the electron energy relaxation length exceeds the characteristic spatial scale of bounded plasmas. The nonlocal method, which is based on the great difference between the electron mean free path for the momentum transfer and the electron energy relaxation length, considerably simplifies the solution of the kinetic equation and, in a number of cases, allows one to obtain analytical and semi-analytical solutions. The main simplification is achieved for trapped electrons by averaging the Boltzmann equation over space and fast electron motion. Numerous examples of spatial nonlocality are considered in the positive column and near the electrodes of DC glow discharges, in spatial relaxation of the electron distribution and in striations, and in capacitively and inductively coupled low-pressure RF discharges. The modeling of fast beam-like electrons is based on a continuous-energy-loss approximation with the assumption of forward scattering. Simple analytic expressions for the fast electron spectrum are obtained in cathode regions of DC discharges with planar and hollow cathodes     

Electron reconstruction in CMS

The reconstruction of the energy and momentum of isolated electrons in CMS combining tracking and electromagnetic calorimetry information is described. The emphasis is put on primary electrons with transverse momentum below 50 GeV/c. The energy deposited in the electromagnetic calorimeter is measured in clusters of clusters (superclusters) which collect bremsstrahlung photons emitted along the electron trajectory in the tracker volume. The electron tracks are built from seeds in the pixel detector found via a cluster-driven pixel hit matching algorithm, followed by a reconstruction of trajectories in the silicon strip tracker with a Gaussian sum filter. Electrons are classified using observables sensitive to the pattern of bremsstrahlung emission and electromagnetic showering in the tracker material. Energy scale corrections depending on the electron class are applied to the supercluster and estimates of associated errors are obtained. The electron energy is deduced from a weighted combination of the corrected supercluster energy and tracker momentum measurements. The electron direction is that of the reconstructed electron track at interaction vertex. The pre-selection of isolated electron candidates for physics analysis is described. Class-dependent observables combining tracking and calorimetry information are discussed for electron identification.     

电荷屏蔽对Ⅱ型超新星瞬时爆发能量的影响

讨论了电荷屏蔽效应对WS15M_⊙前身星模型瞬时爆发能量的影响,对电子俘获率的计算基于平均重核模型,数值模拟表明电荷屏蔽降低了电子俘获率,延长了爆发时间,使中微子泄漏的总能量增加,从而导致激波的能量略微降低.给出的方法可以适用于其他考虑电荷屏蔽效应的超新星数值模拟. 关键词： 超新星 瞬时爆发 数值模拟 电荷屏蔽     

电子束注入简单磁镜中被电子迴旋共振加热捕获的实验研究

在简单磁镜MM-2中,在采用15GHz大功率迴旋管进行电子迴旋共振加热(ECRH)的同时,以不同的方式向磁镜中注入电子束,进行了ECRH捕获电子束的实验研究。结果表明:由于电子束的提前注入,等离子体的预电离时间被大大地缩短。由上ECRH对电子束的捕获,使得热电子环参数得到很大的改善,热电子环的反磁β值约增加62%,对应反磁增加的捕获效率约为(30—40)%。在迴旋管输出约30kW的条件下,适应建立热电环的气体压力窗为(4.67—21.3)×10^-4Pa。 关键词：