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研究了在托卡马克装置中中性束注入时快离子自举电流的产生。利用快离子分布函数在两小增量δ=ρp/a (ρp是极向拉莫尔半径,a是小半径)和δ*=τB/τs(τB是俘获粒子反弹周期,τs是慢化时间)下进行展开的方法求解漂移动力学方程;给出了快离子自举电流的一般表达式。计算了圆截面大纵横比托卡马克中快离子自举电流密度分布和总的快离子自举电流的大小,研究表明：在中性束垂直注入时快离子自举电流约占总电流10%;自举电流的大小既敏感地依赖于中性束注入的角度——平行注入时较小、接近垂直时迅速增大,同时也较强的依赖于快离子的产生速度与临界速度的比值,即vb/vc,而vb2∝E(束能量);自举电流的大小随注入束能量的增加而迅速增大。     

Crystal effects in the neutralization of He+ ions in the low energy ion scattering regime

Investigating possible crystal effects in ion scattering from elemental surfaces, measurements of the positive ion fraction P+ are reported for He+ ions scattered from single and polycrystalline Cu surfaces. In the Auger neutralization regime, the ion yield is determined by scattering from the outermost atomic layer. For Cu(110) P+ exceeds that for polycrystalline Cu by up to a factor of 2.5, thus exhibiting a strong crystal effect. It is much less pronounced at higher energies, i.e., in the reionization regime. However, there a completely different angular dependence of the ion yield is observed for poly- and single crystals, due to massive subsurface contributions in nonchanneling directions.     

Self-consistent LDA calculation in ion neutralization at metal surfaces

The neutralization of He⁺ scattered off aluminum is calculated via a self-consistent LDA where the metal surface is modeled by an LDA jellium surface, and its structure factor is consistently calculated. This approach includes Auger and plasmon-assisted neutralization channels of He⁺ to the He ground state in front of aluminum. We analyze these neutralization channels, which leads us to a revision of the usual calculations of ion neutralization on surfaces depending on the transferred energy lying below, near, or above the metal plasma frequency. The results of this calculation are compared with those of other methods, namely usual unscreened calculations, calculations which extrapolate bulk results, calculations performed for a step potential surface, and surface calculations in the long-distance limit.     

Influence of ion species ratio on grid-enhanced plasma source ion implantation

Grid-enhanced plasma source ion implantation (GEPSII) is a newly proposed technique to modify the inner-surface properties of a cylindrical bore. In this paper, a two-ion fluid model describing nitrogen molecular ions N_2^+ and atomic ions N^+ is used to investigate the ion sheath dynamics between the grid electrode and the inner surface of a cylindrical bore during the GEPSII process, which is an extension of our previous calculations in which only N_2^+ was considered. Calculations are concentrated on the results of ion dose and impact energy on the target for different ion species ratios in the core plasma. The calculated results show that more atomic ions N^+ in the core plasma can raise the ion impact energy and reduce the ion dose on the target.     

Multiple ion scattering

The energy spectra and the angular distributions of noble gas ions, reflected from a metal surface, yield information about a number of important properties of this surface. A large number of investigations have been carried out in the past decades, not only to get insight into the interaction mechanism but also to develop methods for applying of the knowledge gained. To obtain information about the outermost surface layer, it appears necessary to use noble gas ions as primary particles, and to detect the scattered particles in the charged state only; the fraction of noble gas ions reaching the detector, after reflection from target atoms in the second layer, is very small because of the high probability of neutralization. However, this is only valid if the initial energy of the incoming ions is relatively low, namely ? 10 KeV. Under certain experimental circumstances it appears justifiable, down to a lower limit of about 20 eV, to conceive the interaction of these ions with the target atoms as single collisions. The relation between the initial energy and the post-collision energy is then very simple if the collision is an elastic one; it depends upon the scattering angle and upon the ratio of the two given masses only and not upon the interaction potential. The shift of the peaks in an energy spectrum is caused by inelastic collisions and is relatively small in the considered energy region. The causes of this shift will be discussed. As opposed to single collisions, the post-collision energies after a multiple collision depend largely upon the interaction potential. Attention will be paid to the search for these potentials. Utilization of the multiple collision phenomenon in the study of surface geometry is hampered by the vibrational motion of the surface atoms. As a result, the energy spectra are blurred and a shift of the so-called quasi-single and quasi-double peaks can occur. Under certain conditions a third peak emerges which can give additional information about the surface vibrations. The intensity of the scattered ions depends upon the cross section for scattering. Recently it has been shown that the relation between this cross section and the initial energy has an oscillating character for certain combinations of incident ions and target atoms. This phenomenon has very important consequences, e.g. in the use of single ion scattering as an analytical tool. To investigate surface structures it appears that single and multiple ion scattering, combined with LEED and AES, can provide valuable information.     

Neutralization process of Xe^q＋ ion grazing on Al（111） surface

A code has been developed to simulate the neutralization and grazing process of slow highly charged ion Xe^q＋ on Al（111） surface under the classical-over-the-barrier model. The image energy gain of Xeq＋ ions are calculated and compared with experiment data. The simulation results of image energy gain are in good agreement with the experiment data. Meanwhile, in the present work, the reflection coefficient of incident Xe^q＋ on Al（111） surface as a function of the incidence angle, energy and charge state is also studied.     

Theory of ion scattering from single crystals

The scattering of He⁺, Ne⁺ and Ar⁺ ions at 600 eV from Ni(110) in the [11̄0] direction is modeled using classical dynamics. The distributions of final scattering angles of the primary ions are displayed as contour plots over the surface impact zone. From the contour plots the regions of the surface that give rise to scattering at specific angles can be isolated. The majority of the inplane scattering arises from collisions of the primary ion with second layer or “valley” atoms. However, to correctly reproduce the experimental energy distribution curves of Heiland and Taglauer (J. Vacuum Sci. Technol. 9 (1971) 620), we must include a simple collision time correction to account for neutralization of the ion beam. This analysis predicts that the ions which collide with second layer atoms of the solid are preferentially neutralized. The energy distributions due to first layer collisions agree well with experiment. We find that a full molecular three dimensional model is needed to describe all of the ion scattering events since for most of the collisions, the ion is simultaneously interacting with at least two atoms of the solid. However, in agreement with other workers we find only a single collision is responsible for the “binary” peak in the energy distribution. In addition the relative scattering intensity at different angles is dependent on having a three-dimensional solid.     

Nano-patterning of perpendicular magnetic recording media by low-energy implantation of chemically reactive ions

Magnetic nano-patterning of perpendicular hard disk media with perpendicular anisotropy, but preserving disk surface planarity, is presented here. Reactive ion implantation is used to locally modify the chemical composition (hence the magnetization and magnetic anisotropy) of the Co/Pd multilayer in irradiated areas. The procedure involves low energy, chemically reactive ion irradiation through a resist mask. Among N, P and As ions, P are shown to be most adequate to obtain optimum bit density and topography flatness for industrial Co/Pd multilayer media. The effect of this ion contributes to isolate perpendicular bits by destroying both anisotropy and magnetic exchange in the irradiated areas. Low ion fluences are effective due to the stabilization of atomic displacement levels by the chemical effect of covalent impurities.     

Search for Hawking radiation in heavy ion collisions

The creation of “white holes” that decay by Hawking radiation has been proposed as one way to achieve the very early thermalization observed in heavy ion collisions at RHIC. The charartistic temperature of the radiations depends only on the ratio of the baryon number to the transverse energy. The yields of pions, kaons, protons and antiprotons measured by BRAHMS in central Au+Au collisions can be described within a thermal model where T drops with rapidity, and beam energy. We find that the chemical freeze-out temperature drops as the ratio of baryon number to energy increases but much more rapidly than predicted by the model.     

New model for ion neutralization at surfaces

We investigate the neutralization of low energy He⁺ ions in close collisions with metal surface atoms. In order to describe the neutralization process as completely as possible, we consider Auger neutralization (AN), resonant neutralization (RN) and resonant ionization (RI). Our calculation agrees well with experimental data and shows that in some metals (like Pd) AN is the dominant process, whereas in others (like Al) RN and RI contribute significantly for energies above the threshold for reionization.     

Energy spectra of 6–32 keV neutral and ionized Ar and He scattered from Au targets; ionized fractions as functions of energy

The neutralization of ions is an important aspect of low energy ion scattering for surface analysis. Electrostatic energy analyzers (ESA) have been used almost exclusively in such work, and information on charge neutralization efficiencies is needed for quantitative interpretation of ESA data. In the past, the occurrence in low energy ion spectra of surface peaks and low backgrounds due to scattering from inside the solid has been attributed to preferential neutralization of ions which penetrate beyond the surface. In the work to be described, a time-of-flight technique was used to measure energy spectra of both neutral and ionized Ar and He scattered at 90° from a polycrystalline gold target. Incident energies of 6–32 keV were used. The energy spectra of neutral Ar scattered from polycrystalline gold exhibit sharp surface peaks, and double scattering shoulders, over this entire energy range. For He there is a gradual downward slope toward lower energy rather than a sharp surface peak. The behavior in both cases is attributed to large scattering cross-sections which cause a loss of beam particles during penetration. A calculation using a $\text{1}\text{r}{}^2$ potential illustrates this effect as a function of energy for helium. In the present experiments we find that the ion fraction of scattered argon does indeed depend on depth of penetration. This is in contrast to the behavior of He and H at higher energies, e.g. 100 keV, in which cases the charge state depends on emergent velocity but not on depth of penetration. The characteristic shapes of ion scattering spectra in this energy range appear to result from both neutralization and beam attenuation inside the target.     

Effect of 30 Mev Li 3+ ion and 8 MeV electron irradiation on n-channel MOSFETs

The effect of 30 v MeV Li 3+ ion and 8 v MeV electron irradiation on the threshold voltage ( V TH ), the voltage shift due to interface trapped charge ( j V Nit ), the voltage shift due to oxide trapped charge ( j V Not ), the density of interface trapped charge ( j N it ), the density of oxide trapped charge ( j N ot ) and the drain saturation current ( I D v Sat ) were studied as a function of fluence. Considerable increase in j N it and j N ot , and decrease in V TH and I D v Sat were observed in both types of irradiation. The observed difference in the properties of Li 3+ ion and electron irradiated MOSFETs are interpreted on the basis of energy loss process associated with the type of radiation. The study showed that the 30 v MeV Li 3+ ion irradiation produce more damage when compared to the 8 v MeV electron irradiation because of the higher electronic energy loss value. High temperature annealing studies showed that trapped charge generated during ion and electron irradiation was annealed out at 500 v °C.     

129Xe30+与Au作用激发的Au M-X射线 与Xe L-X射线

探测了动能为1.0——7.0 MeV的¹²⁹Xe³⁰⁺ 入射Au表面产生的X射线谱. 实验结果表明, 入射离子动能较高时, 不仅激发出很强的Au的M-X射线, 还激发出了Xe的L-X射线, 且X射线产额与入射离子动能有强相关性. 分析了X射线产额与入射离子动能的关系.     

Isotope effect on the stereodynamics for the collision reaction H＋LiF（v = 0, j = 0） → HF＋Li

Stereodynamics for the reaction H+LiF(v=0, j=0) → HF+Li and its isotopic variants on the ground-state (1 2 A′) potential energy surface (PES) are studied by employing the quasi-classical trajectory (QCT) method. At a collision energy of 1.0 eV, product rotational angular momentum distributions P (θr), P (φr), and P (θr ,φr), are calculated in the center-of-mass (CM) frame. The results demonstrate that the product rotational angular momentum j′ is not only aligned along the direction perpendicular to the reagent relative velocity vector k, but also oriented along the negative y axis. The four generalized polarization-dependent differential cross sections (PDDCSs) are also computed. The PDDCS 00 distribution shows a preferential forward scattering for the product angular distribution in each of the three isotopic reactions, which indicates that the title collision reaction is a direct reaction mechanism. The isotope effect on the stereodynamics is revealed and discussed in detail.     

Dependence of scattered ion yield on the incident energy: Ne on pure gallium and indium

An experimental study of the ion yield dependence on the incident energy (0.4-2.2 keV) for Ne⁺ isotopes scattered at 120° from pure gallium and indium targets has been carried out by mass-resolved ion-scattering spectrometry. For both two targets, the ion yield curves exhibited a broad maximum below 0.8-1 keV (with a lower position for Ne⁺ on In) followed by a monotonous decrease yield without any oscillatory features. The energy dependence of ion-survival probability was explained as a complex interplay of the Auger neutralization with the characteristic velocity v_c=(0.9±0.1)×10⁷ cm/s for Ne⁺ on Ga, and the collision-induced neutralization and reionization. The later ones were significant processes at the energies larger than 0.8-1.0 keV or, in terms of the distance of closest approach, d?0.5-0.55 Å; the collision-induced neutralization was more effective than the inverse process. No visible influence of isotope effect on charge exchange was found. The ion-survival probability versus the inverse ion velocity displayed an independence on the mass of Ne⁺ projectiles.     

外加磁场对碰撞射频鞘层离子能量分布的影响

采用双流体模型,数值研究入射到射频鞘层偏压电极上的离子能量分布.研究结果表明：磁场在改变离子运动状态的同时,调控着基板上的离子能量分布,使之在垂直基板方向和平行基板方向间转移. 关键词： 等离子体 射频 鞘层 磁场     

Correlated electron effects in low energy Sr(+) ion scattering

Resonant charge transfer during low energy ion scattering reveals correlated-electron behavior at high temperature. The valence electron of a singly charged alkaline-earth ion is a magnetic impurity that interacts with the continuum of many-body excitations in the metal, leading to Kondo and mixed valence resonances near the Fermi energy. The occupation of these resonances is acutely sensitive to the surface temperature, which results in a marked temperature dependence of the ion neutralization. We report such a dependence for low energy Sr(+) scattered from polycrystalline gold.     

Effects of downstream magnetic field collimation on ion behavior inelectron cyclotron resonance microwave plasma

Effects of a magnetic held collimation on ion behavior in the downstream region of an electron cyclotron resonance (ECR) plasma device are clarified experimentally using a directional ion energy analyzer. The drift energy and its spread of the ion beam observed in the downstream region decrease and the beam temperature increases with the collimating magnetic flux density. Then, the ion temperature measured perpendicular to the axis of the plasma stream slightly decreases. The ion beam is found to be almost parallel to the magnetic field lines, that is, the beam tends to be collimated     

Unidirectional expansion of lattice parameters in GaN induced by ion implantation

This paper reports that the 150-keV Mn ions are implanted into GaN thin film grown on Al2O3 by metal-organic chemical vapour deposition.The X-ray diffraction reciprocal spacing mapping is applied to study the lattice parameter variation upon implantation and post-annealing.After implantation,a significant expansion is observed in the perpendicular direction.The lattice strain in perpendicular direction strongly depends on ion fluence and implantation geometry and can be partially relaxed by post-annealing.While in the parallel direction,the lattice parameter approximately keeps the same as the unimplanted GaN,which is independent of ion fluence,implantation geometry and post-annealing temperature.     

Plasma immersion ion implantation with dielectric substrates

Plasma immersion ion implantation (PIII) is a novel implantation technique for high-dose/high-current implants. Using the SPICE circuit simulator to model the PIII process, the sheath voltage and ion energy distribution are examined. Implanting into a dielectric substrate results in a significant voltage buildup in the wafer, reducing the effective implant energy. Increasing the pulse voltage raises the dose/pulse, but at the cost of an expanded implant energy spread. Increasing the plasma ion density also raises the dose/pulse, but at the cost of a wider implant energy spread and a lower coupling efficiency. Increasing the substrate thickness reduces both the coupling efficiency and dose/pulse while broadening the energy spread. The large voltage generated across the dielectric substrate decreases the charge neutralization time significantly, reducing the possibility of gate oxide damage