Measurement of Electron Densities and Temperatures in the Plasma Boundary Combining Neutral Beam Probes and Laser-Induced Fluorescence

A new diagnostic method using both techniques of neutral beam probing and laser-induced fluorescence (LIF) is proposed to measure electron density (1011-1013 cm-3) and electron temperature (1-100 eV) of a boundary layer plasma in devices like tokamaks. The local electron density can be obtained by measuring the photon flux of the resonance line produced by electron impact excitation of an injected neutral Li-beam which is produced by laser-induced evaporation (LIE). The density of the neutral Li-beam which is necessary for the determination of the electron density is measured by LIF. The local electron temperature can be obtained by determining the attenuation of two neutral beams (Li, and Al or Ti) produced by LIE, of which the measurements are carried out by means of LIF. The applicability of this method to the TEXTOR tokamak is discussed in detail.     

激光聚变黑腔中等离子体的热流研究

辐射流体采用限流的局域Spitzer-Harm(S-H)电子热流近似,在预估等离子体状态时可能与实验观察存在偏差.利用一维(1D3V)含碰撞的粒子模拟程序,研究了激光聚变黑腔中金等离子体的电子分布函数和电子热流.分析表明,在等离子体的冕区,α=Z(νos/νte)^2>1,电子分布函数表现为超高斯分布(m=3.34),克努森数λe/Le=0.011大于局域S-H理论的临界值2×10^-3.这导致了局域S-H电子热流远大于实际热流.这种实际热流受限现象将导致辐射流体模拟给出的冕区电子温度高于神光实验测量值.而在等离子体的高密度区域,电子分布函数仍表现为超高斯分布(m=2.93),克努森数λe/Le=7.58×10^-4小于局域S-H理论的临界值,限流的局域S-H电子热流具有一定的适用性.但电子热流严重依赖于限流因子,辐射流体模拟需要根据不同位置的光强和电子温度调整的大小.     

脉冲光纤激光修锐青铜金刚石砂轮等离子体特性研究

采用光栅光谱仪 对脉冲光纤激光修锐青铜金刚石砂轮过程中产生的等离子体空间分辨发射光谱进行了测量. 研究了500–600 nm波段范围内的等离子体空间发射光谱强度随激光平均功率和脉冲重复频率的变化情况. 结果表明: 等离子体辐射光谱强度在其径向膨胀方向上距离砂轮表面约2.4 mm处达到最大值. 在局部热力学平衡假设条件下, 根据等离子体中六条铜原子谱线的相对强度, 利用Boltzmann 图法, 计算得到在不同激光功率和重复频 率条件下的等离子体电子温度沿砂轮径向方向的分布规律. 实验结果表明: 在激光修锐青铜金刚石砂轮过程中, 距离砂轮表面约3 mm处等离子体电子温度出现峰值, 其温度最高可达4380 K, 且等离子体电子温度随着激光参数和 空间位置的改变呈现出不同的演变规律. 关键词： 脉冲光纤激光 等离子体发射光谱 激光修锐 电子温度     

A novel raster-scanning method to fabricate ultra-fine cross-gratings for the generation of electron beam moiré fringe patterns

The resolution of the electron beam moiré method depends on the line frequency of the grating. Recently, more and more effort has been devoted to increase the frequency, and a novel method for producing high-resolution electron beam gratings is presented in this work. Cross-gratings with a frequency up to 14,832 lines/mm (67 nm pitch) were successfully fabricated using a common scanning electron microscope without a dedicated pattern generation system. The quality of the grating was high enough to produce high-quality moiré fringe patterns. In this method, the ultra-fine cross-grating can be fabricated only through one-directional scanning on the resist, which can improve the grating quality and significantly reduces the fabrication time. The number of control parameters for grating fabrication could be reduced to two compared to the six parameters required by conventional methods, which facilitates the use of the electron beam moiré method. The frequency of the fabricated grating is linearly proportional to the exposure magnification. Thus, the frequency of the grating can be accurately predetermined, and the null field can be easily obtained in the electron beam moiré method. The quality of the fabricated gratings was illustrated by the obtained micrographs and moiré fringe patterns. The full-field local strain near an induced crack was studied to verify the application potential of this method.     

Theoretical and Experimental Investigations of the Suitability of Low‐Current Z‐Pinch Plasma as an Absorption Medium for Laser Radiation

In this study the electron density of z‐pinch plasmas driven at relatively low currents (ca. 2‐5 kA) was determined using only emission spectroscopy. The suitability of a hollow‐cathode‐triggered z‐pinch plasma as an absorption medium for laser radiation was investigated. The temporal and spatial behaviors of electron temperature and density profiles were estimated using magnetohydrodynamic (MHD) simulations to evaluate the experimental results. Temperature measurements were performed according to the Boltzmann plot method in the visible spectrum range, using the fact that, in low‐current z‐pinch plasma, a local thermodynamic equilibrium prevails for states at high principal quantum numbers (partial local thermodynamic equilibrium). In this case, the Saha equation can be used to determine the electron density. The results demonstrate that this method of determining the electron temperature and density of z‐pinch plasmas is only applicable during the pinching phase. However, in this case the experimentally determined values are in fairly good agreement with the values determined using the MHD model. A user‐oriented 1‐D radiation MHD code was used to simulate the dynamic evolution of the plasma. The experimentally determined maximum electron temperature of approximately 12 eV is in fairly good agreement with the simulated value. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Role of buried ultra thin interlayer silicide on the growth of Ni film on Si(100) substrate

The presence of a buried, ultra-thin amorphous interlayer in the interface of room temperature deposited Ni film with a crystalline Si(100) substrate has been observed using cross sectional transmission electron microscopy (XTEM). The electron density of the interlayer silicide is found to be 2.02 e/?³ by specular X-ray reflectivity (XRR) measurements. X-ray diffraction (XRD) is used to investigate the growth of deposited Ni film on the buried ultra-thin silicide layer. The Ni film is found to be highly textured in an Ni(111) plane. The enthalpy of formation of the Ni/Si system is calculated using Miedema’s model to explain the role of amorphous interlayer silicide on the growth of textured Ni film. The local temperature of the interlayer silicide is calculated using enthalpy of formation and the average heat capacity of Ni and Si. The local temperature is around 1042 K if the interlayer compound is Ni₃Si and the local temperature is 1389 K if the interlayer compound is Ni₂Si. The surface mobility of the further deposited Ni atoms is enhanced due to the local temperature rise of the amorphous interlayer and produced highly textured Ni film. Received: 2 March 2000 / Accepted: 28 March 2000 / Published online: 11 May 2000     

Local trimer orbital ordering in LiNiO2 studied by quantitative convergent beam electron diffraction technique

A local trimer orbital ordering model of LiNiO₂ was studied by means of theoretical calculation and experimental measurement of electron structure factors. Based on the trimer model, the electron structure factors were calculated by using the scattering factor of non-spherical Ni³⁺ ion. From these results, it is found that the effect of local orbital ordering on the electron structure factors of several subtle reflections, such as (202) and (107), is very large. The electron structure factors of these subtle reflections were measured by quantitative convergent beam electron diffraction method. The experimentally measured electron structure factor values of these reflections indicate that the trimer orbital ordering model is more close to the true structure of LiNiO₂.     

Hartree-Fock interaction between a helium atom and lithium metal: A test for the effective medium theory

The interaction of a helium atom with 6 and 10 atom clusters of lithium has been calculated using the unrestricted Hartree-Fock method, Hartree-Fock method with correlation corrections, and the effective medium theory. Inside the cluster the helium embedding energy is found to be proportional to the electron density of the cluster. The proportionality constant obtained by the Hartree-Fock method is in fair agreement with that calculated in the homogeneous electron gas using the local density approximation. Outside the cluster, in the region compatible with the helium diffraction experiments, the self-consistent calculations give much larger repulsion than the effective medium theory.     

Local thermal conductivity of polycrystalline AlN ceramics measured by scanning thermal microscopy and complementary scanning electron microscopy techniques

The local thermal conductivity of polycrystalline aluminum nitride (AlN) ceramics is measured and imaged by using a scanning thermal microscope (SThM) and complementary scanning electron microscope (SEM) based techniques at room temperature. The quantitative thermal conductivity for the AlN sample is gained by using a SThM with a spatial resolution of sub-micrometer scale through using the 3ω method. A thermal conductivity of 308 W/m·K within grains corresponding to that of high-purity single crystal AlN is obtained. The slight differences in thermal conduction between the adjacent grains are found to result from crystallographic misorientations, as demonstrated in the electron backscattered diffraction. A much lower thermal conductivity at the grain boundary is due to impurities and defects enriched in these sites, as indicated by energy dispersive X-ray spectroscopy.     

三温方程中的电子-辐射能量交换项的计算

讨论了激光靶耦合数值模拟中电子-辐射能量交换项的处理。为了克服它给三温方程求解带来的困难,在非平衡区(T_e>T_r)和接近平衡区(T_e~T_r)采用了不同的能量交换项形式。此外,由于接近平衡时的能量交换项用辐射平均自由程表示,避免了此时计算束缚电子占据概率不准确的问题。     

The electronic structure and properties of the C15 compounds CeAl2, LaAl2 and YAl2

Results of self-consistent band calculations are reported for the C15 structured XAl₂ materials (X = Y, La, and Ce) using the local spin density functional formalism for assumed ferromagnetic and antiferromagnetic states as well as the paramagnetic state. The X-atoms are found to be the dominant factor is determining the electronic structure near the Fermi energy and this is enhanced by the presence of f-bands close to (LaAl₂) or at (CeAl₂) the Fermi energy. In paramagnetic CeAl₂, the f-bands are about 1 eV wide and, although principally above the Fermi energy, extend down to accomodate the additional electron compared to LaAl₂. The ferromagnetic state is found not to be stable. By contrast, the antiferromagnetic state is found to be stable with a magnetic moment of 0.88μ_B per Ce atom in very good agreement with the maximum moment, 0.89μ_B found in the neutron measurements of Barbara et al. A significant narrowing of the f-bandwidth is observed in the antiferromagnetic state. The antiferromagnetic spin density ordering appears to be related to nesting features in this underlying Fermi surface in LaAl₂ (i.e., no 4f electron) rather than that of CeAl₂.     

Surface plasmon dispersion in simple metals: a sum rule approach

The local density functional theory and the moment sum rule method are used to calculate the momentum dispersion of surface plasmons in simple metals represented by the stabilized-jellium model. The crystal lattice effects incorporated by this model are found to increase the plasmon frequency of high electron density metals for larger wave vector. Results for the stabilized jellium are compared with experimental data and previous jellium calculations performed by using the sum rule technique and/or the time-dependent local density approach.     

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.     

Numerical simulation of the creation of a hollow neutral-hydrogen channel by an electron beam

An experimental method is proposed for the creation of plasma optical waveguides at low electron densities. The method consists of creating a hollow neutral-hydrogen channel by means of fast local heating of a hydrogen volume by a needlelike electron beam, followed by laser ionization of the hydrogen to provide the plasma waveguide. Results of numerical simulations are presented which show that guiding with an axial electron density in the range of 10(17) cm-3 can be achieved with a matched spot size of 30 microm. Its application for laser wakefield acceleration of electrons is discussed. The method would enable guiding lengths up to 30 cm at maximal energies of accelerated electrons in the range 10-100 GeV.     

Electron doping induced stable ferromagnetism in two-dimensional GdI3 monolayer

As a two-dimensional material with a hollow hexatomic ring structure, Néel-type anti-ferromagnetic (AFM) GdI₃ can be used as a theoretical model to study the effect of electron doping. Based on first-principles calculations, we find that the Fermi surface nesting occurs when more than 1/3 electron per Gd is doped, resulting in the failure to obtain a stable ferromagnetic (FM) state. More interestingly, GdI₃ with appropriate Mg/Ca doping (1/6 Mg/Ca per Gd) turns to be half-metallic FM state. This AFM−FM transition results from the transfer of doped electrons to the spatially expanded Gd-5d orbital, which leads to the FM coupling of local half-full Gd-4f electrons through 5d−4f hybridization. Moreover, the shortened Gd−Gd length is the key to the formation of the stable ferromagnetic coupling. Our method provides new insights into obtaining stable FM materials from AFM materials.     

纳米Sr2SiO4∶Eu3+荧光粉的燃烧法合成及光谱性质

利用快速燃烧合成方法制备了Sr2SiO4∶Eu3+纳米材料.用X射线粉末衍射、扫描电镜、稳态激发与发射光谱、高分辨发射光谱、位置选择激发光谱和发光衰减等测量对材料的结构、形貌和光致发光性质进行了研究.分析结果表明,通过二甲酰肼的快速燃烧,在800℃条件下反应3 min即可制得颗粒尺寸在80～100nm左右的α-Sr2S...     

无箔二极管结构设计研究

用数值计算方法研究了无箔二极管中几何结构参量对束流的影响，得出了无箔二极管结构参数选择的部分规律，同时又结合实际给出了一个无箱二级管模型的最佳组合参数．     

Parametric X-ray radiation as a beam size monitor

We propose two new approaches, referred to as the local and remote methods, for measuring electron beam sizes using parametric X-ray radiation. Using the local method, we have carried out a proof-of-principle experiment, and good agreement was obtained with the results of a standard method using a fluorescent screen. For the remote method, we have proposed a scheme to measure beam sizes using a Fresnel zone plate as an X-ray lens. These methods may prove useful for measuring the sizes of electron beams with small emittances or short bunch lengths in recent advanced accelerators.     

Electron beam damage studies of synthetic 6-line ferrihydrite and ferritin molecule cores within a human liver biopsy

In order to achieve an accurate understanding of the crystal structure of 6-line ferrihydrite (6LFh) and ferritin molecule cores within a human liver biopsy using transmission electron microscopy (TEM), electron beam damage should be considered. For the case of 6LFh, the electron energy loss near-edge structure (ELNES) of core ionisation edges in the electron energy loss spectrum (EELS) combined with multiple linear least-square (MLLS) fitting of reference spectra together with analysis of selected area electron diffraction (SAED) patterns suggests that the iron in 6LFh is solely octahedrally coordinated Fe3+. With increasing electron dose, an increasing percentage of this octahedrally coordinated Fe3+ migrates to tetrahedral sites. When the dose exceeds 3 x 10(8) electrons/nm2, Fe2+ is found to be present in the material. This method also indicates that the iron in ferritin molecule cores within a human liver biopsy is the same as in 6LFh, entirely Fe3+ in octahedral coordination with oxygen. Again the percentage of octahedrally coordinated Fe3+ decreases as the accumulated electron dose increases and Fe2+ is produced in the liver biopsies when the electron dose exceeds 10(6)electrons/nm2.     

用离焦4f差分干涉仪测量等离子体壳层电子密度

 将环型横向剪切干涉仪置于两个镜头之间,由此设计出一种新型的离焦4f差分干涉仪,该干涉仪同时具有分离光路的剪切量和条纹空间频率分别可调的优点以及共光路结构的稳定性和易于调节的优点,使得在测量大密度梯度等离子体的密度分布时,可以在不降低空间分辨率的条件下仍保证干涉条纹可读。在DPF装置上进行了实验,获得了等离子体壳层的干涉图样,计算了等离子体的径向电子密度分布,在内电极端面上方测量到的最高电子密度约为1.2×10¹⁹ cm^-3,外围等离子体壳层的电子密度约为2×10¹⁸ cm^-3。