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为了研究靶材料对快电子能量分布的影响,采用电子谱仪测量了飞秒激光与Cu和CH靶相互作用中在靶前和靶后产生的快电子能谱。结果显示,在靶前Cu和CH靶的快电子能谱相似,反应了快电子发射对靶材料的依赖性较弱;在靶后Cu和CH靶的快电子能谱具有明显的差异,说明电子的输运过程与靶材料密切相关。冷电子环流以及自生磁场是导致Cu靶快电子能谱"软化"的原因,而对于CH靶麦克斯韦分布的快电子能谱主要由碰撞机制决定。     

基于激光等离子体加速的自由电子激光研究新进展

激光等离子体加速器能够在cm尺度内产生GeV量级的高品质电子束,为研制台式化自由电子激光提供驱动源。但是受限于激光等离子体加速中的难点和现有技术发展,电子束的品质难以达到自由电子激光的需求,尤其在稳定性、发散角和能散等方面,阻碍了台式化自由电子激光的研制。介绍了基于激光等离子体加速器的自由电子激光的最新进展,整理了目前高增益自由电子激光实验过程中存在的主要挑战和对应的解决方案与实验进展,并展望未来的发展方向。最近的研究结果证明,通过控制和优化激光等离子体加速器的注入和加速过程产生的高品质电子束可以在指数增益区域实现自发辐射放大,产生高增益的辐射,这也推动基于激光等离子体加速器的自由电子激光研究进入了一个新的阶段。     

The electron’s self photon

Equations of motion (EOM’s) are presented for the electron and photon. The electron EOM is the same as Dirac’s equation with mass interpreted to be totally electromagnetic in nature. The photon EOM is considered here to be the EOM for the electron’s self photon. The electron EOM and photon EOM together are presented as a single theory of the electron which is distinct from QED, in which separate matter and light theories are used for the electron and photon respectively.A temporarily bound state is found for the point proton-electron-self-photon three-body combination which possibly represents a neutronic state. In support of this surmise the theory is used to calculate the neutronic state-proton mass difference, the lifetime of the neutronic state against electron emission, and the neutronic state’s magnetic moment. This interpretation of the neutronic state suggests that the self photon and the neutrino share the same EOM and are possibly the same particle.     

Bound excess electron states on subcritical size helium clusters in a magnetic field

Stable bound electron states are shown to arise on a helium cluster in an external magnetic field. They are qualitatively different from surface bound electron states and are stable for subcritical size helium clusters, for which there are no bound electron states in the absence of a magnetic field.     

Triple differential cross-sections for the fast electron/positron impact ionization of hydrogen and helium in the Glauber approximation

Triple differential cross-section for electron and positron impact ionization of hydrogen and helium are calculated by using the Glauber approximation along with post-collision interaction effects which are estimated classically. The present results are compared with the recent absolute data of Ehrhardt, Jung and coworkers for the electron impact case. The positron impact case is found to lead to a larger binary to recoil peak maxima ratio (compared to the electron impact case) which further increases when post-collision interaction effects are included.     

Oblique Electron Thermal Waves in a Magnetized Plasma

Propagations of an oblique electron thermal mode under the electron plasma frequency without boundary effects are investigated experimentally and theoretically in a magnetized plasma. The phase, ray, and group velocity surfaces of the electron thermal mode are obtained in a polar coordinate. The experimental observation of the electron mode radiated from a point source is found to be in fair accord with the theoretical wave fronts which are obtained from the ray velocity surface. Wave fronts and ray trajectories of an oblique electron thermal mode radiated from a point source are numerically obtained in an inhomogeneous magnetized plasma with a use of an electrostatic kinetic theory. The spatial numerical results are indicated mainly below the electron plasma and cyclotron frequencies. Reflections of the mode in the plasma density lower than the electron plasma frequency are made clear numerically.     

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研究了强激光等离子体中多光子非线性Compton效应下阻尼电子与光子的散射特性,推出了其微分散射截面表达式。研究表明,尾波场的涨落和随机误差是电子发生纵向群聚的根本原因,且能引起电子更剧烈的群聚。电子横向动量的变化是引起电子和光子散射的根本原因,其微分散射截面随与一个电子同时作用的光子数的增大而减小,随散射非弹性成分的增大而迅速减小,但比激光场中的情况来得慢一些。只有当与电子同时作用的光子数与散射非弹性成分相等时电子才能被光场俘获。     

Correlation effects in two electron photoemission

Many-body effects in solids are ultimately related to the correlation among electrons, which can be probed by double photoelectron emission. We have investigated the electron pair emission from a Cu(111) surface upon photon absorption. We are able to observe for the first time the full extension and shape of a depletion zone around the fixed emission direction of one electron. It has an angular extension of approximately 1.2 rad, which is independent of the electron energy.     

Runaway electrons and Generation of high-power subnanosecond electron beams in dense gases

Works on the physics of electron runaway in gases, developing a new understanding of formation of runaway electron beams in gas discharge, are reviewed. Results of experiments with atmospheric-pressure gas-filled diodes, in which subnanosecond electron beams with a record current amplitude were obtained, are reported. The properties of volume nanosecond discharge, allowing to obtain such beams, are analyzed.     

Hamiltonian model of a free electron laser including high-density effects

Both the Compton and the Raman regimes of a free electron laser are described by a relativistic Hamiltonian which originates the evolution equations for 2N+2 canonically conjugate electron and field variables, with the space coordinate as the independent variable. Space charge and field contribution to electron transverse velocity are included.     

Confinement of an Electron in an Image Potential and an External Electrostatic Field

The quasi-classical approximation is used to determine the positions of the classical turning points upon motion of an electron that is bound by an image field and a constant homogeneous electric field of the same direction. Power expansions of the coordinates of the turning points in a wide range of electron energies and field strengths are obtained. The mechanism of one-dimensional confinement of an electron, which determines a completely discrete spectrum of states, is described. The dependence of the spatial width of the confinement region on the field strength and electron energy is determined. The dependences of the electron energy in different states on the external field strength are calculated numerically. Quasi-classical quantization is performed, and the dependence of the electron energy on the width of the confinement region is determined. The energy interval of a maximum density of electron states is found, which is determined by the dependence of the width of the confinement region on the electric field strength.     

Experimental determination of energy resolution and transmission characteristics of an electrostatic toroidal spectrometer adapted to a standard scanning electron microscope

The main characteristics of sectorial toroidal energy analyzer for a new electrostatic electron spectrometer adapted to a standard scanning electron microscope are defined and determined experimentally. These transfer characteristics, i.e. intensity-energy response and transmission functions, energy resolution and coupling constant, are needed for spectrometer calibration, registration and energy correction of measured backscattered electron spectra and microtomographic analysis of multilayered structures. The spectrometer response to a monoenergetic primary electron beam and to a continuous energy distribution is discussed. Detector response functions for energy independent and linear energy dependent detectors are considered. For aperture slits of the spectrometer which allow reasonable electron intensities at the detector an energy resolution of about 2.5% is obtained.     

Observation of electron diffraction due to a reflection grating in an electron wave transistor

We investigate quantum transport in the presence of an electron reflection grating fabricated in an electron wave transistor structure. The grating is made up of a periodically corrugated potential wall by which the electron waves are coherently scattered. We observe a number of peaks with respect to the gate voltage in the low-temperature conductance measurements. The conductance oscillations are attributed to the electron diffraction effect, and the peak positions agree well with those predicted by the Fraunhofer diffraction condition.     

Experimental Study of Planar Langmuir Probe Characteristics in Electron Current-Carrying Magnetized Plasma

Experimental study of planar Langmuir probe characteristics in a magnetized plasma with an electron current along the direction of the magnetic field shows that the usual procedure for determination of the electron temperature and plasma density, which is applicable in a current-free magnetized plasma, gives erroneous results for these plasma parameters. When this procedure is applied on the characteristics measured at two opposite orientations of the probe collecting surface with respect to the direction of the electron drift, different values of the electron temperature are obtained. These virtual electron temperatures and corresponding plasma densities calculated from the measured ion saturation currents are higher and/or smaller than the exact local electron temperature and plasma density. Calculation of particular averages of these quantities is proposed as a possible way to obtain correct results for the local electron temperature and plasma density. These averages are used in the approximate evaluation of the electron drift velocity from the electron saturation currents measured at the two orientations of the probe collecting surface.     

Biprismainterferenzen mit langsamen Elektronen

Diffraction patterns of low energy electrons (150 eV) were observed with an electron interferometer. An interferometer of special design was developed for this purpose. The electron source is reduced in size by a retardation lens, which simultaneously decelerates the electrons down to about 150 eV. The electron beam is split up by an electrostatic biprism (filament diameter 10 μ ¦) in two coherent waves, which recombine behind the biprism giving a Fresnel diffraction pattern. Then the electrons are accelerated and the interference fringes are electron optically magnified. In comparison with an interferometer for high energy electrons the intensity on the viewing screen is higher.     

相对论电子束在动态加载等离子体中的自聚焦传输

为了进一步研究相对论电子束-离子通道辐射实验和理论的需要, 研究了相对论电子束入射中性气体以及通过碰撞电离动态加载等离子体实现对高能束流的自聚焦传输过程PIC(particle in cell) 模拟发现, 电子束电离出的离子背景能够实现对电子束的聚焦传输. 但是离子背景横向和纵向的不均匀性对束流的传输特性有显著影响. 在此基础之上, 提出了电子束在横向不均匀离子背景中传输的理论模型, 给出了束流的自聚焦条件.数值计算结果表明, 横向不均匀性会导致电子束的混合相位传输, 使得焦点附近内层电子可能跑到电子束外而被散焦损失, 这与PIC模拟的结果相符. 此外, PIC模拟还发现, 由于电子束的自聚焦, 在焦点处将电离出更多的离子而引起纵向不均匀性, 纵向不均匀性使得碰撞后的低能电子被俘获, 俘获电子效应会大幅降低电子束的传输效率. 但是俘获电子在纵向呈准周期分布, 对传输电子起到静电Wiggler场的作用, 可能实现静电Wiggler场的动态加载. 研究结果对于进一步研究电子束-等离子体系统的实验以及理论模型提出有一定的参考价值.     

Exploring the third dimension: Volume electron microscopy comes of age

Groundbreaking advances in volume electron microscopy and specimen preparation are enabling the 3-dimensional visualisation of specimens with unprecedented detail, and driving a gratifying resurgence of interest in the ultrastructural examination of cellular systems. Serial section techniques, previously the domain of specialists, are becoming increasingly automated with the development of systems such as the automatic tape-collecting ultramicrotome, and serial blockface and focused ion beam scanning electron microscopes. These changes are rapidly broadening the scope of biomedical studies to which volume electron microscopy techniques can be applied beyond the brain. Further innovations in microscope design are also in the pipeline, which have the potential to enhance the speed and quality of data collection. The recent introduction of integrated light and electron microscopy systems will revolutionise correlative light and volume electron microscopy studies, by enabling the sequential collection of data from light and electron imaging modalities without intermediate specimen manipulation. In doing so, the acquisition of comprehensive functional information and direct correlation with ultrastructural details within a 3-dimensional reference space will become routine. The prospects for volume electron microscopy are therefore bright, and the stage is set for a challenging and exciting future.     

掺镧锆锡钛酸铅陶瓷极化强度变化量对电子发射电流强度的影响

铁电阴极因其优异的电子发射性能在高功率微波管的电子束源、平板显示技术以及宇航推进器等领域 有着广阔应用前景而日益受到人们的重视.大量研究表明,铁电阴极电子发射性能受阴极材料性能的影响. 在激励电场作用下,铁电阴极材料会产生表面非屏蔽电荷而引起极化强度的变化, 这表明铁电阴极电子发射性能可能与阴极材料的极化强度变化量存在着某种关系. 为研究阴极材料极化强度变化量对铁电阴极电子发射性能的影响,以掺镧锆锡钛酸铅铁电和反铁电陶瓷样品 作为阴极材料,通过正半周电滞回线测试得到阴极材料在不同电场强度下的极化强度变化量, 测量得到电子发射电流强度随激励电场的变化曲线,并分析了电子发射电流强度与极化强度变化量的关系. 结果表明,两种样品电子发射电流强度与极化强度变化量正相关.     

Electron beam induced surface activation: a method for the lithographic fabrication of nanostructures via catalytic processes

In focused electron beam induced processing (FEBIP), the very narrow electron beam of a scanning electron microscope or transmission electron microscope is used to locally modify matter on the nanometer scale. Recently, the family of FEBIP could be considerably expanded by the technique of focused electron beam induced surface activation (EBISA). In EBISA, the surface itself gets chemically activated by the impact of the electron beam without the presence of precursor molecules. In the second EBISA processing step, the surface is exposed to a precursor molecule which is then catalytically decomposed at the pre-irradiated/activated areas and eventually continues to grow autocatalytically upon prolonged precursor dosage. In this way, electron irradiation and precursor dosage are effectively separated. One of the advantages is that, due to the autocatalytic growth, the size of the corresponding nanostructures can be controlled by the precursor dosage and corresponding electron proximity effects can be omitted. Another advantage is the parallel processing of the pre-irradiated regions during precursor dosage. This bears the potential to significantly reduce the fabrication times for larger deposits compared to the classical electron beam induced deposition approach, in which precursor molecules are sequentially dissociated by the impact of the electron. The fundamentals and apparent further developments as well as the potential and challenges of the comparably new EBISA technique, and more general of catalytic effects in FEBIP are presented and discussed.