电子束离子阱中高价态离子演化过程的数值模拟

讨论了电子束离子阱(EBIT)中决定高价态离子演化过程的主要物理机制.对EBIT中高价态离 子的演化过程进行了详细的数值计算并与实验进行了比较.讨论了EBIT各种不同的运行参数 对平衡时高价态离子相对丰度和温度的影响. 关键词： 电子束离子阱 高价态离子 数值模拟     

高Z类锂离子禁戒跃迁研究

电子束离子阱(EBIT)是一种可以产生周期表中任意元素的任意高电荷态离子的实验室的装置。而在高电荷态离子的情况下，由于磁偶极和电四极禁戒跃迁速率与Z的高次幂成正比增长会变得很大，致使有些禁戒跃迁在极重离子极高电荷态下可以与光学允许跃迁相比拟，从而禁戒跃迁不再禁戒，因此有必要在双电子复合、不透明度、自由程等理论计算中考虑其影响。     

电子束离子阱及高电荷态离子相关物理

文章简要介绍了电子束离子阱（EBIT）的发展背景及其在国际上的状况，较详细地解释了它的结构和工作原理，介绍了它在分解研究等离子体方面的特别优势以及在EBIT上能够实现的高电荷态离子相关的前沿物理学问题研究。     

极化效应对Bohr速度能区O5+离子在低密度氢等离子体中的能损影响

基于HIRFL加速器装置的低能束实验平台,实验测量了1.07 MeV(～66.9 keV/u)高电荷态O⁵⁺离子穿过中性氢气和部分电离的低密度氢等离子体靶后的能量损失,观测到等离子体中离子能损减小的新实验现象.分别考虑部分电离等离子体对炮弹离子的电荷屏蔽效应以及靶区原子的极化效应(Barkas修正),重新计算了离子能损,讨论了离子能损减小的可能物理机制.研究结果表明:在部分电离的低密度等离子体中,靶区的原子极化效应将显著影响Bohr速度能区离子的能量损失过程.     

气体放电阴极鞘层氩离子的自洽蒙特卡罗模拟

建立了气体放电阴极鞘层离子的自洽蒙特卡罗模拟模型,考虑了离子与中性原子的电荷交换碰撞和弹性散射,用到了精确依赖于离子能量的电荷交换和动量输运截面。模拟了氩离子在阴极鞘层中的运动,得到了不同气压下自治电场分布,离子的能量分布和角分布,发现:离子由鞘层边界向阴极运动过程中,离子能量分布的高能部分逐渐增大,角分布向小角度部分压缩,鞘层中的强电场加速和聚焦了离子;在鞘层边界附近的电场呈非线性。     

气体放电空心阴极鞘层氩离子的蒙特-卡罗模拟研究

建立了气体放电空心圆筒阴极鞘层离子的自洽蒙特-卡罗模拟模型,对鞘层区内离子的输运过程进行了研究。考虑了离子与中性原子的电荷交换碰撞和弹性散射,用到了精确依赖于离子能量的电荷交换和动量输运截面。模拟了氩离子在空心阴极鞘层中的运动,得到了不同放电条件下自洽电场分布,离子的能量分布,角分布以及电子密度分布和离子密度分布。计算结果表明:离子在由鞘层边界向阴极运动过程中,离子能量分布的高能部分逐渐增大,角分布向小角度部分压缩,鞘层中的强电场对离子起加速和聚焦作用;在鞘层内离子密度分布比较均匀,只是在鞘层边界附近变化 关键词：     

PA和PPP三嵌段共聚物的带电态研究

采用半经验的Austin Model 1(AM1)方法,计算了-(PA)₄-(PPP)_m-(PA)₄-共聚物的带电状态,该系列共聚物具有典型的阱垒阱结构特征.与中性态相比,带电态下其分子结构表现为C—C键长发生显著的改变.在不同的掺杂浓度及不同的势垒宽度下,电荷在势阱中的分布是不同的. 关键词： 共聚物 有机量子阱 带电态 键长     

ECR微波等离子体离子输运的数值模拟

建立了ECR微波等离子体源离子输运的平板和圆柱模型,对离子历经的空间区域的输运过程进行了数值研究。采用Monte Carlo(M-C)方法模拟了存在外磁场情况下,离子离开开放电室后历经中性区、鞘层区、最后被加负偏压的工作表面吸收的全过程,考虑了离子与中性粒子的电荷交换碰撞玫弱性散性,统一处理了中性区和鞘层区电势的衔接,采用曲线拟合,电势自洽迭代方法把中性区和鞘层区衔接起来,得到了光滑自治的电势分布曲线和鞘层区不同位置处的速度分布、能量分布及角分布。     

Paul阱中基态低能多离化Fen+(n=1-3)离子的存储及反应特性

利用垂直交叉的激光束在Paul阱中溅射固体铸铁(FeC)靶,产生了低能多电荷铁离子Fen+(n=1-3),得到了Fe3+离子在本底气压为3.0×10-7Pa下的衰减速率(0.96s-1)以及在1.3×10-5Pa下和中性气体分子N2的反应产物.     

等离子体源离子注入球形靶的蒙特-卡罗模拟

建立了在球形靶鞘层中离子的蒙特-卡罗模拟模型,考虑了离子与中性粒子的电荷交换碰撞和弹性散射,以及精确依赖于入射离子能量的电荷交换碰撞截面和动量输运截面。模拟了不同气压下,在鞘层扩展过程中,氮离子N_2~+到达靶表面的能量分布和入射角分布,研究了它们的变化规律。     

Effect of residual gas on the ion charge distribution in vacuum arc discharge plasmas

A magnetic mass analyzer and time-of-flight mass spectrometer are used to study the effect of the pressure and type of residual gas on the ion charge distribution in the plasma of an arc discharge with a cathode spot. The possibility of ionizing a substantial fraction of the gas atoms in this type of discharge is pointed out. Zh. Tekh. Fiz. 68, 24–28 (September 1998)     

Non-vacuum field desorption ion source implemented under super-atmospheric pressure

Standard field desorption (FD) ionization is implemented under high vacuum condition. In this paper, non-vacuum FD is performed under a super-atmospheric pressure environment using untreated tungsten wires as FD emitter, and the ion source was coupled to a commercial linear ion trap mass spectrometer. The operating pressure of the ion source was 6 bars which was high enough to provide sufficient dielectric strength to the working gas so that the high voltage that was required for FD could be applied to the emitter without occurrence of electrical discharge. Non-volatile sample deposited on the bare tungsten wire FD emitter was heated by flowing direct current through the emitter. Similar to vacuum FD, the formation of conical protrusion of the liquefied sample layer under the strong electric field was also observed. Using the present ion source, high pressure field-desorption of polar neutral compounds, organic salts and ionic liquids is demonstrated. Copyright ? 2012 John Wiley & Sons, Ltd.     

Dipolar excitons in a potential trap in a magnetic field

The conditions for observing the Zeeman spin splitting compensation in an exciton Bose gas have been investigated. The magnetoluminescence of spatially indirect, dipolar excitons in a 25-nm-wide GaAs/AlGaAs quantum well upon their accumulation in a lateral electrostatic trap has been studied in the Faraday geometry. The critical magnetic field B _cr below which the spin (paramagnetic) splitting of the luminescence line for a heavy-hole exciton at the trap center is almost completely compensated due to the exchange interaction in a dense Bose gas has been found to increase linearly with exciton concentration in qualitative agreement with the theory. Using a potential trap is fundamentally important. Incomplete compensation is observed in a homogeneous photoexcitation spot for dipolar excitons: the splitting is considerably smaller than that for a spatially direct exciton but differs noticeably from zero. The spin splitting compensation effect is observed only under neutral charge balance conditions—there is no Zeeman splitting suppression in a charged quantum well.     

Loss of cold atoms due to collisions with residual gases in free flight in a magneto-optical trap

The loss rate of cold atoms in a trap due to residual gas collisions differs from that in a free state after the cold atoms are released from the trap. In this paper, the loss rate in a cold rubidium-87 atom cloud was measured in a magneto-optical trap(MOT) and during its free flight. The residual gas pressure was analyzed by a residual gas analyzer, and the pressure distribution in a vacuum chamber was numerically calculated by the angular coefficient method. The decay factor, which describes the decay behavior of cold atoms due to residual gas collisions during a free flight, was calculated. It was found that the decay factor agrees well with theoretical predictions under various vacuum conditions.     

Buffer-gas-cooled ion clouds in a classical Paul trap: superimposed stability diagrams and trapping capacity investigations

Ion clouds of different species and variable size are stored in a 3D Paul trap and detected after extraction from the trap. We report on measurements of the superimposed stability regions of four simultaneously stored ion species. We determine the operating conditions for trapping capacity under variation of buffer gas pressure and observe space charge shifts for a specific ion in the presence of other elements.     

Spatial and Temporal Characteristics of an Excimer Laser-Induced Lead Plasma Emission

A laser-induced plasma was generated from a lead target using an ArF excimer laser (λ = 193 nm) and characterized by time-resolved and time-integrated spatially resolved spectrometry. The ambient atmosphere (gas composition and pressure) influenced the emission intensity for both atomic and ionic lines. The emission of laser-induced lead plasma varied with time as well as the location in the plasma. Lead ion emission decayed more rapidly than lead atomic line emission. High excitation temperatures and nonlinear optical phenomena were observed in the laser-induced lead plasma. Gas breakdown and the subsequent shielding effect of the incident laser beam in different ambient gas compositions and pressures were discussed to explain the different efficiency of metal ion for matioa in the plasma. The experimental results show that spatial discrimination of the laser-induced plasma emission is desirable for direct spectrochemical analysis.     

Dust in Plasma I. Particle Size and Ion‐Neutral Collision Effects

A fully kinetic self‐consistent model of an absorbing particle immersed in stationary isotropic weakly collisional plasma has been developed. The combined effects of particle size and ion‐neutral charge exchange collisions have been investigated for intermediate regimes, where no analytic theories are available. It is shown that collisional effects related to the ion orbital destruction (presence of extrema in ion flux collected on the particle surface and in particle potential and charge) are important for small particles, while they are totally absent for large particles. The potential distribution around the particle is quite well represented by a Yukawa form, but with an effective screening length that shows different dependences from the gas pressure for small and large particle size. Analytical fitting formulas of particle charge and potential and screening length depending on the particle radius parameter and on the Knudsen number have been obtained (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Fluorescence Detection and Buffer Gas Cooling of Trapped Mercury Ions in Paul Trap

Pig ions are confined in a hyperboloid ion trap. With the rf discharge ^202 Hg isotope lamp, the fluorescence signal of trapped Hg ions is observed. By means of buffer gas cooling, the ionic temperature is reduced. As a result, the trapping time is increased and the signal-to-noise ratio （SNR） of the fluorescent signal is improved. The temperature of ion cloud is estimated by measuring the space charge shift.     

Ion-beam focusing in a double-plasma device

The authors studied the propagation of a low-energy charge-neutralized ion beam injected into the target region of a long double-plasma device. A magnetic field of up to ~180 G may be applied along the axis of the device. As a result of charge exchange collisions, the ion beam is attenuated as it propagates into the target region. However, under certain conditions of magnetic field strength and neutral gas pressure, the authors have observed a `reemergence' of the beam on axis far downstream in the target. This reemergence of the ion beam is attributed to a focusing of the ions by a self-consistently produced radial ambipolar electric field. The effect may be expected to occur in other types of plasma devices as well, whenever a sufficiently large radially inward electric field is present     

Determination of an optimal pressure under field emission from diamondlike films

A model accounting for anomalously high field emission of electrons from diamondlike films in a rough vacuum is suggested. This effect is shown to be associated with a positive ion charge forming on the film. The ions arise because of residual gas ionization in the electrode gap. The pressure maximizing the emission current is determined.