空间电荷效应对时间展宽分幅变像管时空性能的影响

X射线分幅相机是惯性约束聚变实验中的重要二维超快诊断设备,具有长漂移区结构的时间展宽分幅相机,在大幅度提升时间分辨性能的同时,会使空间电荷效应时空弥散变大。为探讨空间电荷效应的影响,以短磁聚焦分幅变像管为例,通过平均场模型和电子轨迹及成像分布研究空间电荷效应的时空弥散,并分析其对像管的影响。研究和分析结果表明,空间电荷效应引起的时间弥散与阴极电压、展宽脉冲斜率和漂移距离有关,空间弥散与成像系统和电子脉冲电流密度相关。当分幅变像管的时间分辨率提升至2ps左右时,空间电荷效应的时间弥散相当于物理时间分辨,成为制约时间分辨性能进一步提升的主要因素,此时像管空间分辨性能降低8%左右。通过对像管空间电荷效应研究及其降低方法的探讨,为亚皮秒时间分辨分幅变像管的研制提供理论参考。     

三维离子阱内空间电荷效应的理论分析

离子阱内存储的大量离子之间会有强烈的库仑相互作用,导致所谓的空间电荷效应,它一直是质谱理论研究和应用领域内非常感兴趣的问题。本工作根据三维离子阱内的离子分布情况,假设离子在三维离子阱的中心区域呈近似于球对称的高斯分布, 通过求解阱内电场所对应的电势函数满足的泊松方程,得到这个球对称高斯分布的离子云所产生的电场解析表达式,在小振动近似下,得到离子运动的久期（secular）频率与阱内离子数目的理论关系。通过进一步应用Mathematica数学模拟软件,计算模拟了不同久期运动频率的离子在不同个数的离子所组成的离子云排斥作用下的久期主频率的移动。计算结果与小振动近似下的理论计算结果基本一致。由于离子阱的质量分析是通过改变离子偶极激发电压实现的,这种频率移动将对离子被激发逸出的电压值产生影响,最终影响离子阱质谱质量分析的准确度。因此,用离子阱质谱进行离子分析时,通过减少存储的离子数以减少空间电荷效应,或根据离子数对质谱测量结果进行校正是有意义的。     

二次离子质谱的一次离子光学系统

二次离子质谱仪作为一种强大的表面分析工具,在表面分析领域有着非常广泛的应用。本文报道了一种用于二次离子质谱仪的一次离子光学系统,它可以对电子轰击电离源产生的一次离子进行有效的加速与聚焦,形成稳定的、能量在0～5kV范围内连续可调的离子束流。同时,该光学系统可以在两种聚焦模式下工作,产生两种不同性能的离子束流。实验结果表明,采用电子轰击电离源作为一次离子源的条件,该离子光学系统能够将离子束聚焦至直径为20μm的束斑,其一次离子束流密度最高可达到503.2mA/cm2,可以实现对一般样品(如材料或生物样品)的表面成分分析。     

两类氟代对三联苯液晶化合物的质谱裂解规律分析

利用气相色谱-质谱联用法（GC/MS）对两类氟代对三联苯共12个液晶化合物进行电子轰击离子化（EI）质谱分析,并总结其裂解规律。氟代对三联苯液晶化合物的主要裂解过程是苄基裂解失去烷基,某些碎片离子会违背偶电子规则进一步生成m/z 274碎片离子。氟原子取代位置会对裂解产生一定的影响,由于氟原子的吸电子诱导效应,在某种程度上改变了对三联苯之间的共轭度,碎片离子的相对丰度会有明显差异。     

双哌嗪盐类化合物电子轰击离子化质谱研究(英文)

对 6个新合成的双哌嗪盐类化合物进行了电子轰击离子化质谱及其裂解规律的研究。研究表明 :通过降低电子轰击电流强度 ,该类化合物的电子轰击离子化质谱的准分子离子和特征碎片峰非常清晰。但 M+和 M2 +离子峰并未出现。在低电子能量条件下 ,发现了 [M-2 ]+,[M-R]+,[M-R-1 ]+,[M-2 R]+,甚至 [RX]+离子峰的存在。这些现象可能与分子内的 R+重排反应有关。进一步尝试提出该类化合物的电子轰击离子化质谱裂解规律 ,为该类化合物的质谱研究提供有用的信息。     

ICP-MS某些问题研究

ＩＣＰ－ＭＳ作为一种新的分析技术,但在应用中存在的问题确不容忽视。研究和探讨一些问题对其进一步推广应用是很有必要的。１信号波动实验结果表明,随着被分析元素质量数的增加,被分析元素质谱信号波动的ＲＳＤ值逐渐减小。即测定中,重元素的精密度要比轻元素的精密度高。这一实验事实可用空间电荷效应来解释。通过截取锥进入质量分析器的离子流为正离子流,空间电荷效应使离子束中的正离子在斥力的作用下而离开离子流中心通道。轻元素离子质量轻被斥偏离量较大;重元素离子质量大,受空间电荷效应影响小。偏离量小;换言之,重离子束…     

溅射中性粒子质谱(SNMS)

溅射中性粒子质谱或称二次中性粒子质谱(SNMS)是一种新的表面分析技术。与二次离子质谱(SIMS)一样,其检测灵敏度高达ppm—ppb。由于中性粒子的溅射产额不受基体的影响,因而SNMS可简单并准确定量。直接轰击模式的SNMS作深度剖析可用能量很低的一次离子轰击源以避免级联混合效应,从而获得极高的深度分辨率。     

基于叠型场线性离子阱的便携式质谱仪研制与应用

介绍了自行研制的基于叠型场线性离子阱的便携式质谱仪结构,以及初步的应用测试。该质谱仪的质量分析器采用叠型场线性离子阱,离子源采用辉光放电电子轰击电离源和介质阻挡放电离子源。仪器重10 kg,功耗低于100 W,体积33 cm×20 cm×20 cm,可以对气体、固体和液体进行检测。挥发性有机气体通过膜进样接口实现大气压直接进样,采用内置的辉光放电电子轰击电离源对其电离。介质阻挡放电离子源作为大气压离子源,通过非连续大气压接口实现质谱的大体积进样,及对枪击残留物DDU和去痛片等的快速检测。     

用于双聚焦磁质谱仪的电子轰击离子源的设计与研究

本文设计了一种用于双聚焦磁质谱仪的电子轰击离子源,运用静电透镜软件simion的仿真模拟研究了它的离子光学系统,研究了离子光学系统电压参数和离子束的初始半散角对拉出离子效率和离子束宽度的影响.     

常压火焰用作质谱电离源的理论探讨

在文献调研的基础上,对常压火焰用做质谱电离源的可行性作了理论上的探讨.常压火焰近似于等离子体,含有丰富的离子和电子,具备成为电离源的必要条件.从离子碎裂反应机理的角度,分析了火焰中样品分子裂解和电离的可能机理,并总结出可能影响电离效率的相关因素.在一定的操作条件下,用常压火焰作质谱电离源,可望获得分析对象不同形态的结构信息.     

Development of electron beam ion source charge breeder for rare isotopes at Californium Rare Isotope Breeder Upgrade

Recently, the Californium Rare Isotope Breeder Upgrade (CARIBU) to the Argonne Tandem Linac Accelerator System (ATLAS) was commissioned and became available for production of rare isotopes. Currently, an electron cyclotron resonance ion source is used as a charge breeder for CARIBU beams. To further increase the intensity and improve the purity of neutron-rich ion beams accelerated by ATLAS, we are developing a high-efficiency charge breeder for CARIBU based on an electron beam ion source (EBIS). The CARIBU EBIS charge breeder will utilize the state-of-the-art EBIS technology recently developed at Brookhaven National Laboratory (BNL). The electron beam current density in the CARIBU EBIS trap will be significantly higher than that in existing operational charge-state breeders based on the EBIS concept. The design of the CARIBU EBIS charge breeder is nearly complete. Long-lead components of the EBIS such as a 6-T superconducting solenoid and an electron gun have been ordered with the delivery schedule in the fall of 2011. Measurements of expected breeding efficiency using the BNL Test EBIS have been performed using a Cs(+) surface ionization ion source for external injection in pulsed mode. In these experiments we have achieved ～70% injection∕extraction efficiency and breeding efficiency into the most abundant charge state of ～17%.     

Ion optics of RHIC electron beam ion source

RHIC electron beam ion source has been commissioned to operate as a versatile ion source on RHIC injection facility supplying ion species from He to Au for Booster. Except for light gaseous elements RHIC EBIS employs ion injection from several external primary ion sources. With electrostatic optics fast switching from one ion species to another can be done on a pulse to pulse mode. The design of an ion optical structure and the results of simulations for different ion species are presented. In the choice of optical elements special attention was paid to spherical aberrations for high-current space charge dominated ion beams. The combination of a gridded lens and a magnet lens in LEBT provides flexibility of optical control for a wide range of ion species to satisfy acceptance parameters of RFQ. The results of ion transmission measurements are presented.     

Study of ion beam transport from the SECRAL electron cyclotron resonance ion source at the Institute of Modern Physics

Ion beam transport from the Superconducting Electron Cyclotron Resonance ion source with Advanced design in Lanzhou (SECRAL) electron cyclotron resonance ion source was studied at the Institute of Modern Physics during 2010. Particle-in-cell simulations and experimental results have shown that both space charge and magnetic aberrations lead to a larger beam envelope and emittance growth. In the existing SECRAL extraction beam line, it has been shown that raising the solenoid lens magnetic field reduces aberrations in the subsequent dipole and results in lower emittance. Detailed beam emittance measurements are presented in this paper.     

The effects of space charge on contrast in images obtained using the environmental scanning electron microscope

We present experimental evidence for the existence of a space charge in the environmental scanning electron microscope. Space charge formation is attributed to differences in the mobilities of negative and positive charge carriers in the imaging gas. A model is proposed for the behavior of space charge during image acquisition. The effects of space charge on images acquired using the gaseous secondary electron detector, ion current, and backscattered electron signals are interpreted using the proposed model.     

Influence of discharge gap on the discharge stability in a short vacuum arc ion source

The influence of the discharge gap between cathode and anode on the discharge stability in a short vacuum arc (SVA) ion source is presented in this paper. Planar cathode and cylindrical hollow anode made of titanium are investigated. There is a great need in present accelerator injection research for SVA source to produce the small deviation of the ion current beam. Current research shows that increasing the short discharge gap can reduce the level of ion current deviation and ion charge deviation from 29% and 31% to 15% and 17%, respectively. A microplasma plume generation mechanism in SVA and scanning electron microscopic results can be used to explain this interesting phenomenon.     

A particle-in-cell Monte Carlo code for electron beam ion source simulation

FAR-TECH, Inc., has developed a particle-in-cell Monte Carlo code (EBIS-PIC) to model ion motions in an electron beam ion source (EBIS). First, a steady state electron beam is simulated by the PBGUNS code (see http://far-tech.com/pbguns/index.html). Then, the injected primary ions and the ions from the background neutral gas are tracked in the trapping region using Monte Carlo method. Atomic collisions and Coulomb collisions are included in the EBIS-PIC model. The space charge potential is updated by solving the Poisson equation each time step. The preliminary simulation results are presented and compared with BNL electron beam test stand (EBTS) fast trapping experiments.     

Liquid metal alloy ion source based metal ion injection into a room-temperature electron beam ion source

We have carried out a series of measurements demonstrating the feasibility of using the Dresden electron beam ion source (EBIS)-A, a table-top sized, permanent magnet technology based electron beam ion source, as a charge breeder. Low charged gold ions from an AuGe liquid metal alloy ion source were injected into the EBIS and re-extracted as highly charged ions, thereby producing charge states as high as Au(60 +). The setup, the charge breeding technique, breeding efficiencies as well as acceptance and emittance studies are presented.     

Wall-loss distribution of charge breeding ions in an electron cyclotron resonance ion source

The ion loss distribution in an electron cyclotron resonance ion source (ECRIS) was investigated to understand the element dependence of the charge breeding efficiency in an electron cyclotron resonance (ECR) charge breeder. The radioactive (111)In(1+) and (140)Xe(1+) ions (typical nonvolatile and volatile elements, respectively) were injected into the ECR charge breeder at the Tokai Radioactive Ion Accelerator Complex to breed their charge states. Their respective residual activities on the sidewall of the cylindrical plasma chamber of the source were measured after charge breeding as functions of the azimuthal angle and longitudinal position and two-dimensional distributions of ions lost during charge breeding in the ECRIS were obtained. These distributions had different azimuthal symmetries. The origins of these different azimuthal symmetries are qualitatively discussed by analyzing the differences and similarities in the observed wall-loss patterns. The implications for improving the charge breeding efficiencies of nonvolatile elements in ECR charge breeders are described. The similarities represent universal ion loss characteristics in an ECR charge breeder, which are different from the loss patterns of electrons on the ECRIS wall.     

Towards a better comprehension of plasma formation and heating in high performances electron cyclotron resonance ion sources (invited)

Further improvements of electron cyclotron resonance ion sources (ECRIS) output currents and average charge state require a deep understanding of electron and ion dynamics in the plasma. This paper will discuss the most recent advances about modeling of non-classical evidences like the sensitivity of electron energy distribution function to the magnetic field detuning, the influence of plasma turbulences on electron heating and ion confinement, the coupling between electron and ion dynamics. All these issues have in common the non-homogeneous distribution of the plasma inside the source: the abrupt density drop at the resonance layer regulates the heating regimes (from collective to turbulent), the beam formation mechanism and emittance. Possible means to boost the performances of future ECRIS will be proposed. In particular, the use of Bernstein waves, in preliminary experiments performed at Laboratori Nazionali del Sud (LNS) on MDIS (microwave discharge ion sources)-type sources, has permitted to sustain largely overdense plasmas enhancing the warm electron temperature, which will make possible in principle the construction of sources for high intensity multicharged ions beams with simplified magnetic structures.     

Charge breeding simulations for radioactive ion beam production

The charge breeding technique is used for radioactive ion beam (RIB) production in order of optimizing the re-acceleration of the radioactive element ions produced by a primary beam in a thick target. Charge breeding is achieved by means of a device capable of increasing the ion charge state from 1+ to a desired value n+. In order to get high intensity RIB, experiments with charge breeding of very high efficiency could be required. To reach this goal, the charge breeding simulation could help to optimize the high charge state production efficiency by finding more proper parameters for the radioactive 1+ ions. In this paper a device based on an electron beam ion source (EBIS) is considered. In order to study that problem, a code already developed for studying the ion selective containment in an EBIS with RF quadrupoles, BRICTEST, has been modified to simulate the ion charge state breeding rate for different 1+ ion injection conditions. Particularly, the charge breeding simulations for an EBIS with a hollow electron beam have been studied.