Observation of a structural transition for Coulomb crystals in a linear Paul trap

A structural transition for laser cooled ion Coulomb crystals in a linear Paul trap just above the stability limit of parametrically resonant excitation of bulk plasma modes has been observed. In contrast to the usual spheroidal shell structures present below the stability limit, the ions arrange in a "string-of-disks" configuration. The spheroidal envelopes of the string-of-disks structures are in agreement with results from cold fluid theory usually valid for ion Coulomb crystals if the ion systems are assumed to be rotating collectively.     

有限磁场作用下等离子体背景中的切伦可夫不稳定性研究

 较高密度的相对论电子束注入等离子体中将会形成离子通道，在考虑了离子通道的影响下，推导出圆柱波导中更普遍的色散方程，并计算出考虑离子通道和不考虑离子通道效应时的色散关系及电磁波的增长率。     

Dispersion relation and growth rate for a corrugated channel free-electron laser with a helical wiggler pump

The effects of corrugated ion channels on electron trajectories and spatial growth rate for a free-electron laser with a one-dimensional helical wiggler have been investigated. Analysis of the steady-state electron trajectories is performed by solving the equations of motion. Our results show that the presence of a corrugated channel shifts the resonance frequency to smaller values of ion channel frequency. The sixth-order dispersion equation describing the coupling between the electrostatic beam mode and the electromagnetic mode has also been derived. The dispersion relation characteristic is analyzed in detail by numerical solution. Results show that the growth rate of instability in the presence of corrugated ion channels can be greatly enhanced relative to the case of an uniform ion channel.     

A Transient-State Simulation of Ionization Effects in a Microwave Tube

A model for studying the ionization effects in a microwave tube has been developed. This model is simulated by a two-dimensional particle-in-cell code with the Mont Carlo collision model for the electron-neutral ionization process. The transient-state process of ion noise and ion focusing effects are observed. A simple theory about ion motion is given for interpreting the phenomenon of the ion moving to the wall of the tube when the beam is not neutralized. The computed result agrees with the experiment and simulation result.     

多靶强流铯溅射离子源的研制

多靶强流铯溅射离子源是多种加速器中常用的离子源之一,在科学研究和工业生产领域的应用十分广泛。但是,目前商业化应用的该种离子源由欧美几个国家垄断,国内还没有厂家能够生产。为了提高加速器运行和建造中的自主化水平,研制了一种多靶强流铯溅射离子源。该离子源主要由离子源腔、换靶装置、冷却系统、控制箱等组成,根据功能需求对其关键部件进行结构设计,采用了全新的伺服电机驱动换靶方式,提供靶位微调功能和远程控制模式,并使用Opera-3D软件模拟优化结构参数和束流光路。经过测试,该离子源在中国原子能科学研究院的400 kV小型加速器质谱(AMS)装置上应用情况良好,换靶定位精准,供束稳定,束流参数达到进口离子源的参数指标,实现了预期目标。     

ToF-SIMS analysis of a fluorocarbon-grafted PET with a gold cluster ion source

Cluster ions have been recognized as a superb primary species in time of flight secondary ion mass spectroscopy (ToF-SIMS) compared with monatomic primary ions, as they significantly enhance the secondary ion yields from bulk samples. Self-assembled monolayers provide an important system for studying the fundamental mechanism involved in the yield enhancement.We used a gold cluster ion source to analyze a new type of self-assembled monolayer: a fluorocarbon-grafted polyethylene terephthalate. In addition to the structure details, which helped to understand the grafting mechanism, ToF-SIMS analysis revealed that fluorocarbon secondary ion yield enhancements by cluster ions were due to the enhanced sputter efficiency. A larger information depth may also be expected from the enhancement. Both mathematical definitions of damage cross-section and disappearance cross-section were revisited under a new context. Another cross-section parameter, sputter cross-section, was introduced to differentiate the beam induced sputter process from damage process.     

Impact of an ion-flux non-uniformity on the sputtering of a target with a surface relief in a glow discharge plasma

The distribution of the sputtering yield averaged over the ion energy and flux density of sputtered atoms in a glow discharge plasma on a surface with a small-amplitude periodic relief has been calculated. The average sputtering yield of the target has a minimum at tops of the relief due to the energy separation of ions within the near-electrode discharge layer, while the flux density of sputtered atoms in this case is maximized due to the higher density of the ion flux on these areas.     

Peculiarities of the electron exchange upon collision of a negative hydrogen ion with a cluster of aluminum atoms

The resonant electronic transition upon normal-to-surface collision of a negative hydrogen ion with a cluster of aluminum atoms has been considered. The dependence of the probability of ion survival on the distance to the cluster surface is calculated for different collision velocities. It is shown that, depending on the incident particle velocity, a cluster of atoms can behave as a bulk sample or a nanostructure with energy quantization over two coordinates.     

Luminescence spectra of a supramolecular complex of uranyl and a star-shaped polymer based on calix[8]arene

The luminescence spectra of the supramolecular complex of an uranyl ion and a ring calix[8] arene polymer have been obtained. It has been found that a significant reconstruction of light-emitting levels takes place in the temperature range 130–180 K. It has been assumed that the observed features are due to excitation transfer between the uranyl ion and the complex-forming polymer.     

Hydromagnetic Stability of a Self-Gravitating Composite Plasma in the Presence of Finite Larmor Radius

The hydromagnetic stability of a self-gravitating composite plasma has been studied to include the effects of ion viscosity and the finiteness of the ion Larmor radius. The whole medium is embedded in a uniform horizontal magnetic field. The F. L. R. effects have been included through the stress tensor. An explicit solution for a semi-infinite plasma of finite depth and with an exponential density variation along the vertical is obtained by means of a variational principle characterizing the problem. Numerical calculations show that the influence of the effects of ion viscosity and F. L. R. is to reduce the growth rate of unstable perturbations. On the other hand the effects of neutral gas collisions have been found to be both stabilizing as well as destabilizing.     

Kinetics of ion admixture in a native gas in an external harmonic electric field

We have considered the spatially homogeneous problem of the behavior of an ion admixture in a background gas after applying a harmonic electric field with arbitrary parameters for various laws of interaction of particles. The Boltzmann equation has been solved using the modified method of moments. The ion distribution function and its first moments have been analyzed. It has been shown that the universal analytic expressions for the current density and the ion energy that we derived earlier for a small field amplitude-tofrequency ratio have a considerably wider range of applications.     

Determining isotopic distributions of fission products with a Penning trap

A novel method to determine independent yields in particle-induced fission employing the ion guide technique and ion counting after a Penning trap has been developed. The method takes advantage of the fact that a Penning trap can be used as a precision mass filter, which allows an unambiguous identification of the fission fragments. The method was tested with 25MeV and 50MeV proton-induced fission of ²³⁸U . The data is internally reproducible with an accuracy of a few per cent. A satisfactory agreement was obtained with older ion guide yield measurements in 25MeV proton-induced fission. The results for Rb and Cs yields in 50MeV proton-induced fission agree with previous measurements performed at an isotope separator equipped with a chemically selective ion source.     

Vibrationally mediated negative differential resistance in a single molecule

Negative ion density fronts have been shown to occur in electronegative steady-state plasmas with hot electrons. In this Letter, we report theoretical and numerical results on the spatiotemporal evolution of negative ion density fronts during plasma ignition and extinction (afterglow). During plasma ignition, the negative ion fronts are analogous to hydrodynamic shocks. This is not the case during plasma extinction where, although negative ions diffuse freely in the plasma core, the negative ion front propagates towards the chamber walls with a nearly constant velocity.     

Generalized dependences of the reflection coefficient of ions from a relief surface

Dependences of the reflection coefficient of ions on their energy and the height and geometry of surface asperities obtained while studying ion beam interaction with targets by the Monte Carlo method have been analyzed. The dependences of the reflection coefficient on the height of asperities with a specified geometry under bombardment with ions of different energies, on the height of asperities for different angles of inclination of lateral walls at a specified energy of ions, and on the angle of inclination of walls for different ion energies at a fixed height have been considered. Generalized curves for reflection coefficients have been obtained, and analytical approximations have been calculated.     

Modulation of the non-linear ion acoustic waves in a plasma consisting of warm ions and isothermal electrons

Summary Modulation of one-dimensional ion acoustic waves in a plasma consisting of a mixture of warm ions and isothermal electrons has been studied using the derivative expansion method. A non-linear Schr?dinger-type equation governing the complex amplitude of the perturbed ion density is obtained. The small-wave-number limit has been considered to compare it with the oscillatory solution of the Korteweg-de Vries equation obtained by Tagare and Lai using the reductive perturbation method. A good agreement has been found.     

Current-voltage characteristics of a gas field ion source

Current-voltage characteristics of a gas field ion source (GFIS) have been measured for hydrogen and all rare gases. The parameter set included tip temperature, tip radius and gas temperature and pressure. This investigation has been made to get a complete overview of the field ion currents (FIC) and to estimate the maximum currents in a GFIS, which have been found to a few 100 nA. This estimate allows also a feasibility study of a GFIS, modified by a supertip, a small protuberance on the emitter surface.     

Transverse oscillations of a long-pulse electron beam on alaser-formed channel

An intense relativistic electron beam may be transported in low-pressure gas using an ion channel which focuses and guides the beam. The beam can be unstable to the growth of transverse oscillations caused by the electric force between the beam and channel-the ion hose instability. Beam propagation on channels created by photoionization of gas with an excimer laser is discussed. Ion hose oscillations have been recorded which have a betatron wavelength of approximately 1.5 m. The growth rate of the ion hose instability in the linear regime was measured as 1.67±0.45. At this level of growth, the amplitude of beam oscillations equals the channel radius after a period of one-third of an ion oscillation time     

磁场中等离子体鞘层的结构

采用流体力学理论，研究了斜磁场作用下的等离子体鞘层结构.在不同大小及方向的磁场作用下，对鞘层的离子，电子密度分布，离子流速度分布，电势分布和Bohm判据进行了讨 论.结果显示磁场对鞘层的结构有明显的影响.在静电力和洛仑兹力的作用下，离子流作螺旋进动，离子密度分布产生振荡. 关键词： 磁鞘 等离子体 磁场     

Modulational instability of a weakly relativistic ion acoustic wave in a warm plasma with nonthermal electrons

An investigation has been made of modulational instability of a nonlinear ion acoustic wave in a weakly relativistic warm unmagnetized nonthermal plasma whose constituents are an inertial ion fluid and nonthermally distributed electrons. Up to the second order of the perturbation theory, a nonlinear Schr?dinger type (NST) equation for the complex amplitude of the perturbed ion density is obtained. The coefficients of this equation show that the relativistic effect, the finite ion temperature and the nonthermal electrons modify the condition of the modulational stability. The association between the small-wavenumber limit of the NST equation and the oscillatory solution of the Korteweg－de Varies equation, obtained by a reductive perturbation theory, is satisfied.     

Reflection coefficient of low-energy ions as a universal function of the scaled transport cross section

Multiple collision theory of heavy ion ranges in an infinite medium has been used to calculate the reflection coefficient from the penetration profile, by a method first described by Bottiger et al. Interaction with target electrons has been neglected and nuclear collisions have been described by the power cross sections. Calculations are restricted to low reduced ion energies )₀А.1 and to target/ion mass ratios 7⢪, when electronic stopping is much less than the nuclear stopping. The Gaussian approximation of the penetration profile and the reflection coefficient are found in a form of simple analytic formulas. Furthermore, the penetration profile was constructed by using Edgeworth expansion and moments of the distribution up to the fourth order, and the reflection coefficient was determined from the profile. Good agreement between the analytical results and the reflection coefficient obtained from Edgeworth expansion was found, for target atom/ion mass ratios 7̿.3. It is shown that the reflection coefficient is a universal function of the scaled transport cross section. The scaling is fulfilled for v̀, when ion reflection is determined by large-angle multiple collisions, and breaks down for v<1 i.e. 7<1, when scattering angles are small. Results are compared with TRIM computer simulation data.