Field extraction of ions from liquid solutions with the use of polymer track membranes

The general principles of the electric field assisted ion evaporation in the membrane ion source are considered. In the ion source, the liquid sample under investigation is placed in narrow channels of a polymer track membrane, which separates the liquid sample at atmospheric pressure from the vacuum chamber. Stability of the liquid at strong electric fields is provided by a choice of the diameters of channels and the liquid–polymer contact angle. The electric charge on the vacuum–polymer interface is of great importance for creation of the strong electric field near the liquid–vacuum interface. Such a conclusion is made from the computations of the electric field in the framework of the model developed. The mechanism of the electric field assisted evaporation of ions is discussed to explain the observed mass spectra for the ions extracted from liquid.     

Extraction of ions from polar solutions by high-strength electric field pulses

Extraction of ions from solutions of salts in ethylene glycol and water-glycerol mixture by high-strength electric field pulses is investigated. The conditions for stable extraction of ions from a polar liquid in the pulsed regime are ensured by using a track membrane with channels of a nanosize diameter as the interface between the liquid solution and vacuum. The possibility of barrier-free field evaporation of ions from polar liquids in electromembrane ion source for mass-spectrometric analysis of solutions is considered.     

Generation of ions in a pulsed ion source with an interface based on a polymer track membrane

The time-of-flight spectra of ions generated during the extraction of negative ions from the KI solution in water–glycerin mixture by high-strength electric field pulses are studied using a source with an interface based on a polymer track membrane. It has been shown that the ions formed in secondary processes of bombardment of the membrane surface make a considerable contribution to the observed spectra. It has been found that the peaks of negative hydrogen ions have the highest intensity in the spectrum, indicating effective emission of these ions during the bombardment of polyethylene terephthalate by secondary ions with an energy of about 6 keV. The main trends in the modification of the membrane interface to reduce the fraction of secondary ions in the ion beam have been outlined.     

Polymer track membranes for atmospheric pressure field extraction of ions from liquid solutions

An approach to the generation of gas phase ions by field extraction from liquid solutions has been investigated. The method uses a polymer membrane with nano-size channels as an interface between the liquid and the atmospheric pressure gas. Ions are produced by dissociation in the polar solvent and secondary ion-molecular reactions in the solution, which fills the channels of the membrane. Field extraction of the ions from the channels is stimulated by pulses of the electric discharge between the membrane and an adjacent electrode in the gas. The gas-phase ions are removed from the extraction zone by air flow and are detected by mass spectrometry. Possibilities of the membrane interface for generation of gas phase ions have been demonstrated from mass spectral investigation curried out for angiotensin II, gramicidin S and cytochrome C solutions. The current kinetics of the membrane ion source has been investigated to elucidate the mechanism of the ion extraction.     

Numerical simulation of ions acceleration and extraction in cyclotron DC-110

In Flerov’s Laboratory of Nuclear Reactions of JINR in the framework of project “Beta” a cyclotron complex for a wide range of applied research in nanotechnology (track membranes, surface modification, etc.) is created. The complex includes a dedicated heavy-ion cyclotron DC-110, which yields intense beams of accelerated ions Ar, Kr and Xe with a fixed energy of 2.5 MeV/A. The cyclotron is equipped with external injection on the base of ECR ion source, a spiral inflector and the system of ions extraction consisting of an electrostatic deflector and a passive magnetic channel. The results of calculations of the beam dynamics in measured magnetic field from the exit of spiral inflector to correcting magnet located outside the accelerator vacuum chamber are presented. It is shown that the design parameters of ion beams at the entrance of correcting magnet will be obtained using false channel, which is a copy of the passive channel, located on the opposite side of the magnetic system. Extraction efficiency of ions will reach 75%.     

Structure of electromagnetic fields near the surface of an ionic crystal

A NaCl ionic crystal whose (100) face is in contact with vacuum is used as an example to consider static and dynamic contributions to an electromagnetic field in close proximity to its surface. The expression for the potential of the electric field produced by a system of point charges in vacuum (derived by Lennard-Jones and Dent) is taken as the basis. The dynamic correction to the static field has been found. It appears as a result of thermal fluctuations of ions near equilibrium positions in the ionic lattice. Various contributions of the electrostatic field of the ionic lattice, the field of fluctuating ions of this lattice near their equilibrium positions, and of the dipole-type fluctuation field produced by spontaneous deformations of the crystal??s elementary cells to the energy density of the electromagnetic field near the surface of the ionic crystal have been calculated and compared. The periodic structuring of the electromagnetic field??s energy density caused by the presence of static and dynamic ionic lattices of the crystal at small distances from its surface is illustrated graphically. Fields generated by a film with a finite thickness containing an arbitrary number of ion monolayers have also been considered.     

Positron emission isotope production cyclotron in DLNP JINR (Status Report)

A C10-cyclotron for radioisotope production is under construction at the Dzhelepov Laboratory of Nuclear Problem, Joint Institute for Nuclear Research (DLNP JINR). It is a compact isochronous cyclotron for accelerating H⁻ ions to the energy of about 10 MeV. The magnetic system, vacuum chamber and accelerating system is being built now. Results of the calculation and forming of the cyclotron magnetic field and the study of the beam dynamics from an ion source to an extraction system in calculated magnetic field are presented. The text was submitted by the authors in English.     

等离子体离子源发射面的理论计算与数值模拟

 等离子体离子源发射面的位置和形状决定了离子束的传输特性,而发射面的位置与形状又取决于等离子体参数、引出电压、电极结构等,并自动地调节到某个平衡状态。介绍了一种2维情况下等离子体离子源发射面的位置与形状的理论计算方法,即非磁化等离子体不能扩散进入外加电场中大于一定临界值的区域,等离子体离子源发射面的位置及形状可以通过直接求解引出系统的Laplace方程而得到。利用基于PIC的OOPIC程序对不同引出结构的发射面位置及形状和引出束流进行了数值模拟,结果与理论计算的结果十分接近。     

Track-membrane-based interface for field evaporation of ions from polar solutions in the diffusion-drift regime

The possibility of realization of barrier-free field evaporation regime for ions from polar solutions in the conditions when the flux of ions from the liquid is limited by their diffusion and drift from the bulk to the surface is considered. The strength of the electric field extracting ions is estimated by simulating electric fields in an ion source with a track membrane as the interface with allowance for the sizes of channels in the membrane and their density. It is shown that when time-dependent electric fields are used, the regime of barrier-free field evaporation can be realized with an appropriate choice of geometrical parameters of the membrane.     

负离子源引出系统束光学的数值模拟

根据在表面-等离子体型负离子源中,负离子主要由转换电极表面产生这一特点,参考正离子源引出系统数值计算程序,建立了负离子源引出系统的数值计算模型和计算程序;对表面-等离子体型桶式负离子源引出系统束光学的性质进行了数值模拟。对计算结果的检验和分析表明,这个计算模型和程序反映了负离子源引出系统束光学的基本特性。     

Calculation of the charge composition of an ion beam from an E-Mevva source

The charge composition of an ion beam from an E-Mevva source is calculated within a model of sequential electron ionization of ions in a vacuum arc plasma. The effect of the plasma initial parameters on the charge composition of the ion beam is studied. Possible charge compositions for more than 30 elements omitted from this article are estimated. Also, the charge composition of the ions is calculated for the ultimate current density of the electron beam.     

Ionization mechanism in a liquid-metal ion source. Source for high-melting metals

Investigations have been made of the ionization mechanism in a liquid-metal ion source. At the instant of ion current generation the surface of a liquid metal emitter frozen in a highvoltage field exhibits microprotrusions pulled from the liquid metal by the electric field. A double-focusing mass spectrometer identified two components in the ion beam extracted from the aperture in the extractor. One ion component forms at the tip of the emitter and has an energy spread not exceeding a few tens of electronvolts. The other ion component forms in the cathode plasma at the extractor. On the basis of these investigations, a mechanism is proposed for ion formation in a liquid metal ion source and this mechanism is used to produce a modified source design. The source can produce ion beams from high-melting metals and nonmetals, and beams of Ta, W, Mo, C, and Fe ions were obtained. Zh. Tekh. Fiz. 67, 82–87 (November 1997)     

磁场调控型离子源的设计与实验

磁场调控型离子源在离子源等离子体扩散空间中引入轴向强脉冲磁场,磁场起两方面的作用,一是形成潘宁放电效应,使原子、气体分子碰撞电离效率增加;二是在脉冲强磁场的作用下,强轴向磁场将质量较轻的离子约束在轴线上,对质量较重的金属离子约束能力较弱,导致其在等离子体膨胀引出通道中碰壁损失,能够提升引出轻离子的比例。开展了磁场调控的离子源放电结构、强脉冲螺线管磁场以及引出束流光学结构的设计;测量分析了引出离子流强和离子打靶束斑形貌。研究结果表明,强轴向磁场通过等离子体对混合离子成分的筛选作用,可有效提高引出离子流强中的轻离子成分比例。     

含氘电极真空弧等离子体空间分布特性诊断研究

真空弧放电等离子体含有多种离子成分,并且各离子在空间上具有不同的分布规律.本文针对金属氘化物电极真空弧离子源,搭建了一台紧凑型磁分析装置,用来研究放电等离子体中氘离子与金属离子的空间分布.当离子源弧流为100 A左右时,该装置能有效地传输引出束流,并且具有较好的二次电子抑制效果,可准确获得各离子流强.利用该装置测量并获得了氘化钛含氘电极真空弧放电等离子体内氘离子和钛离子空间分布规律,结果表明:径向上,氘离子和钛离子都呈高斯分布,但氘离子分布均匀,而钛离子相对集中在轴线附近,导致轴线附近氘离子比例最低;轴向上,所有离子数量都以自然指数函数减少,而且相对幅度接近,所以氘离子比例几乎不变.本文研究结果不仅有助于理解真空弧放电等离子体膨胀过程,还可以指导金属氘化物电极真空弧离子源及其引出设计.     

离子注入层的X射线光电子能谱分析

采用金属蒸汽真空弧（MEVVA）离子源发出的强束流脉冲钨离子,对H13钢进行了离子注入表面改性研究,借助X射线光电子能谱（XPS）考察了注入表面层中钨,氧,铁的化学状态,研究发现,钨离子注入层中钨元素以替位钨和三氧化钨形式存在,铁元素以金属铁和三氧化二铁形式出现,而且各价态元素的原子比随深度而变化。     

中子管用潘宁离子源氢负离子产生机理及实验研究

为了克服目前潘宁(PIG)离子源中子管引出正离子所带来的诸多不利因素,使用PIG型氢负离子源作为中子管的离子源,研究了氢负离子产生的机理,以期在中子管中获得应用。给出了PIG离子源结构,根据氢负离子产生的方式和条件,结合CST软件仿真实验,确定在对阴极和引出孔附近区域存在氢负离子,而且是氢负离子密度比较大的区域。实验中,通过负离子源产生系统证实了氢负离子的存在及分布规律,中子监测仪测量自成靶50mm负离子源陶瓷中子管,中子产额较传统正离子中子管高出一个数量级以上。     

Electron beam extraction from a broad-beam vacuum-arc metal plasmasource

We describe experiments demonstrating the formation of a high current electron beam from a vacuum arc plasma. A preexisting vacuum arc ion source was used, with the extraction voltage reversed in polarity so as to form an electron beam rather than an ion beam; no other changes were required. The beam formed was of energy up to 33 keV, beam current up to 70 A, beam diameter about 10 cm, pulse width 500 μs, and energy density up to 25 J/cm². This kind of source can be used for material surface modification     

Dynamics of an ion flow in an electron layer

We study the acceleration of an ion flow in the electron layer formed by an electron flow moving in a transverse electric field and confined by the intrinsic magnetic field. The possibility of extraction of heavy ions with velocities lower than the ion sound velocity from the plasma, and the feasibility of their further acceleration by an external field is demonstrated.     

Low-Voltage Membrane Interface for Ion Extraction from Polar Solutions

Electric field that extracts ions from polar solutions to gas phase is calculated for membrane interface with electrode located on the vacuum surface of the membrane. Such a structure can be used to significantly decrease the voltage that provides efficient emission of ions from solution filling the membrane channel and, hence, improve the characteristics of membrane interface.     

2 cm电子回旋共振离子推力器离子源中磁场对等离子体特性与壁面电流影响的数值模拟

电子回旋共振离子推力器(electron cyclotron resonance ion thruster,ECRIT)离子源内等离子体分布会影响束流引出,而磁场结构决定的ECR区与天线的相对位置共同影响了等离子体分布.在鞘层作用下,等离子体中的离子或电子被加速对壁面产生溅射,形成壁面离子或电子电流,造成壁面磨损和等离子体损失,因此研究壁面电流与等离子体特征十分重要.为此本文建立2 cm ECRIT的粒子PIC/MCC(particle-in-cell with Monte Carlo collision)仿真模型,数值模拟研究磁场结构对离子源内等离子体与壁面电流特性的影响.计算表明,当ECR区位于天线上游时,等离子体集中在天线上游和内外磁环间,栅极前离子密度最低,故离子源引出束流、磁环端面电流和天线壁面电流较低.ECR区位于天线下游时,天线和栅极上游附近的等离子体密度较高,故离子源引出束流、天线壁面电流和磁环端面电流较高.腔体壁面等离子体分布与电流受磁场影响最小.