Einzel Lens Research Articles

Development and commissioning of ion-optical elements for ion and antiproton beams with energies up to 5 keV

In nuclear and atomic physics experiments, charged ion beams often need to be guided from the ion production to the experimental site. In the PUMA experiment, an ion source beamline was developed, which can be operated with up to 5 keV beam energy at a base pressure of 10-9 mbar or better. In this technical report, a low-energy pulsed drift tube for beam energy modification, a hybrid einzel lens assembly for beam focusing and steering and an iris shutter assembly for separating beamline sections with different vacuum requirements are described with their design principles and performances.

Design of electrostatic lenses through genetic algorithm and particle swarm optimisation methods integrated with differential algebra

Genetic algorithm (GA) and particle swarm optimisation (PSO) techniques have been integrated with the differential algebra (DA) method in charged particle optics to optimise an Einzel lens. The DA method is a robust and efficient tool for the calculation of aberration coefficients of electrostatic lenses, which makes use of nonstandard analysis for ray tracing a particle as it is subjected to the field generated by a lens. In this study, initial populations of lenses with random geometrical configurations are generated. These initial populations are then subjected to GA and PSO algorithms to alter the geometry of each lens for a set number of iterations. The lens performance is evaluated by calculating the spot size using the aberrations coefficients up to third-order generated by the DA method. Moreover, a focusing column comprising two lenses and a Wien filter was optimised using GA method.

Design and characterization of a compact Einzel lens for portable quadrupole mass spectrometry (QMS)

Quadrupole mass spectrometry (QMS) offers better resolution, selectivity and sensitivity than the metal-oxide, field effect transistors and thermal-based gas sensors. However, existing QMS systems are unsuitable for field applications. The miniaturized QMS requires dimensionally scaled components with comparable performance to the conventional bulky systems. For a portable quadrupole mass spectrometry, a compact focusing ion system is required to transfer the maximum number of ions from the ion source to the filter. The present paper discusses the design of a miniature focusing Einzel lens and the effect of design parameters on its performance. The three-cylindrical axially symmetric compact Einzel lens assembly was designed using commercially available software. The relationship between the design parameters is explored for compact and low-powered ion optics. The beam focal length was tuned by varying the bias voltage. The dimensions, as well as voltages across the Einzel lens, were reduced significantly to open a new way for portable point-of-care applications. At an applied voltage of 70 V, the focal length of the ions is 11 mm without being scattered, which is favorable for a portable quadrupole mass filter. The designed Einzel lens was fabricated using micromachining techniques and characterized at a vacuum of 3.05 × 10−4 mbar. The developed lens system shows a current output of 0.114 µA at 72 V lens voltage. A current of 94.8 µA is observed with a background noise of 0.01 µA for the system with nitrogen (28 amu) as the sample.

Controllable variable beam diameter ion source based on the Einzel lens

With the development of modern optical systems, high-power laser systems, ultraviolet lithography systems, etc., the requirements for the precision and processing efficiency of optical components continue to increase. Although sub-nanometer precision can be achieved with current ion beam figuring, the introduction of additional removal layers greatly limits its machining efficiency due to the inability of the machine dynamics to satisfy the velocity and acceleration requirements mathematically. Therefore, an efficient figuring technology of controllable variable beam diameter ion beam based on the Einzel lens has been proposed. The simulation results show that the ion beam diameter can be effectively controlled by adjusting the voltage of the Einzel lens. The experimental results show that the ion source can control the ion beam diameter by voltage, and then change the size of the ion beam, and obtain a very small removal function. The FWHM is reduced from 12.1 mm to 10.1 mm, and the peak removal rate is increased by 1.7 times, which significantly improves the removal efficiency and figuring ability. Therefore, this work aims to improve the accuracy of ion beam figuring of high-power laser optical components and address the problem of reduced efficiency caused by additional removal layers in the existing figuring process.

Design and performance of a low-emittance electron gun for electron beam probe

An Electron Beam Probe (EBP) is preferable to provide a non-interceptive measurement of the transverse distribution of a dense bunched ion beam. During EBP operation, it was observed that the electron beam spot subjects to expansion when scanned across the ion beam due to the strong space charge field of the ion bunch, leading to significant degradation of spatial resolution. To mitigate this effect, a small electron beam spot is beneficial as demonstrated in previous research. This paper presents design details of a low-emittance, small-spot, and long-work-distance electron gun. Geometry optimization of the gun and focus lens is conducted using a multiobjective genetic algorithm (MOGA) interfaced with space charge simulation codes to maintain normalized thermal emittance within an acceptable increase and achieve a small spot at a long work distance. The emittance is measured using a slit-screen technique, resulting in a norm. rms emittance of 0.046(+-0.005) um*rad under low beam current conditions (50 nA). In high-resolution mode, a beam spot size of 0.6 mm (rms) is achieved at a work distance of 1.2 m with the combination of Einzel lens and solenoid. The gun has been successfully operated as part of EBP experiments for accurate and high-resolution measurement of ion beam width, demonstrating excellent agreement with wire scanner measurements with relative deviation not exceeding 1%.

An improved source of spin-polarized electrons based on spin exchange in optically pumped rubidium vapor

We have improved a polarized electron source in which unpolarized electrons undergo collisions with a mixture of buffer gas molecules and optically spin-polarized Rb atoms. With a nitrogen buffer gas, the source reliably provides spin polarization between 15% and 25% with beam currents >4 μA. Vacuum pump upgrades mitigate problems caused by denatured diffusion pump oil, leading to longer run times. A new differential pumping scheme allows the use of higher buffer gas pressures up to 800 mTorr. With a new optics layout, the Rb polarization is continuously monitored by a probe laser and improved pump laser power provides more constant high polarization. We have implemented an einzel lens to better control the energy of the electrons delivered to the target chamber and to preferentially select electron populations of higher polarization. The source is designed for studies of biologically relevant chiral molecule samples, which can poison photoemission-based GaAs polarized electron sources at very low partial pressures. It operates adjacent to a target chamber that rises to pressures as high as 10−4 Torr and has been implemented in a first experiment with chiral cysteine targets.

Beam optics simulation of the ion injector for sodium Beam Emission Spectroscopy (Na-BES) on EAST

To upgrade the Li-BES to Na-BES on Experimental Advanced Superconducting Tokamak (EAST), a high-brightness and stable sodium (Na) ion source is developed, and the performance of Na ion beam optics is simulated by the COMSOL Multiphysics. The porous tungsten disk with 70% porosity and filled with albite Na2O·Al2O3·6SiO2 is successfully developed as the Na ion source. The extracted current density of the Na-beam increases with the extraction voltage, and its maximum current can reach 9 mA with the ion source diameter of 20 mm. The lifetime of the Na ion source is evaluated to be 63 mAh, which is much longer than that of the Li ion source. The simulation shows that the preferable distances among the ion source (or anode electrode), extractor and puller to get the well-focused beam are x puller - x extractor ∼ 0.06 m and x extractor - x ion source ∼ 0.02 m. Further simulation with these optimized distances determines the extraction voltage and ion source size for good beam performance. In addition, the simulation shows the beam divergence angle decreases by more than 40% by optimizing the Einzel voltage to 5 kV, suggesting an excellent focusing property of the Einzel lens. These works provide the basis and the design references for the Na-BES development on EAST.

A simple in situ method for optimizing settings for the Einzel lens elements in a focused ion beam.

Ion beams have had an incredible impact on research in the past couple of decades. One major reason for this is the continued development of systems having optimal beam currents that allows one to image more clearly at different spot sizes to include higher currents that allow for faster milling. The advancements for Focused ion beam (FIB) columns have developed rapidly due to the computational optimization of lens designs. However, once a system has been produced, the optimal column settings for these lenses may change or simply become obscure. Our work involves regaining this optimization with the newly applied values through a new algorithm, requiring hours, rather than the days or weeks that existing methods require. FIB columns frequently utilize electrostatic lens elements (normally two, condenser and objective). This work presents a method to quickly determine the optimal lens 1 (L1) values for large beam currents (∼1 nA or greater), from a carefully acquired set of images without any detailed knowledge of the column geometry. Each set of images, acquired through a voltage sweep of the objective lens (L2) for a preset L1, is partitioned for its spectral content. The sharpest position at each spectral level is used to assess how close the preset L1 is to the optimal. This procedure is conducted for a range of L1 values, the optimal being the one having the smallest range in spectral sharpness. For a system that has suitable automation in place, the time to optimize L1 for a given beam energy and aperture diameter is ∼1.5 h or less. In addition to the technique for finding optimal condenser and objective lens parameters, an alternative peak determination method is presented.

Ion microscopy with evolutionary-algorithm-based autofocusing

Ion microscopy is an established technique for laser focus diagnostics and the accurate, intensity-resolved measurement of laser ionization processes. In the present feasibility study, we discuss a new ion microscope design, which improves its resolution across a large range of magnifications and simplifies its operation. Instead of the common two einzel lens configuration, which is usually optimized for a fixed magnification, we propose a generic design consisting of an array of equally spaced ring electrodes, whose individually adjustable voltages are controlled by an evolutionary algorithm. In this way, we can realize aberration minimized magnifications between 25 and 100. Moreover, the algorithm can adjust the voltage settings under changing experimental conditions and facilitates autofocusing for user-defined magnification.

Post collision analyzer to study charge-exchange processes in ion-molecule collisions.

We have designed an electrostatic charge state analyzer for ion beams having energies in the range of 5-20 keV/q. It is primarily built to investigate the different ionization processes involved in the slow (v < 1 a.u.) impact of highly charged ions on molecules. The analyzer is a cylindrical deflector analyzer (CDA) based on a pair of concentric cylindrical sectors of radii 110.2 and 95mm, subtending an angle of 127° at its center. Additionally, an Einzel lens and a quadrupole deflector are deployed to focus and steer the ion beam. The compact design of the analyzer permits easy integration with an ion momentum spectrometer used for studying the fragmentation of the target molecules. The characterization of the CDA including its calibration and its transmission function is carried out using an ion beam delivered from an electron beam ion source. To check the performance of the setup, we have carried out experiments comprising the impact of Ar16+ projectiles on CO2 target molecules at an energy of 18 keV/q. With the help of the CDA, different charge exchange ionization processes, such as single capture, double capture, and triple capture of electrons by the projectile ion have been separated efficiently. The possibility of a modification in the geometry of CDA is discussed to further improve its performance.

Improved limit of detection of a high-resolution fs-LIMS instrument through mass-selective beam blanking

Laser Ablation Ionisation Mass Spectrometry (LIMS) is an important quantitative method for chemical analysis of solids. Current limits of detections (LoDs) of LIMS instruments are in the ppm to sub-ppm range (atomic fractions), while other commonly used techniques for solid sample analysis reach LoDs at ppb levels or even below. This study presents the implementation of mass-selective beam blanking in the Laser Mass Spectrometer – Gran Turismo (LMS-GT) to improve the instruments’ detection limit. LMS-GT is a high-performance time-of-flight LIMS instrument coupled to a femtosecond laser ablation ion source reaching micrometre spatial resolutions and mass resolutions ≳ 12′000. A fast high voltage switch was developed in-house to induce potential changes at an Einzel lens at the intermediate time focus of the ion trajectory, leading to short deflections of the ion beam and hindering selected species from reaching the detector. The intensities of single mass lines are reduced with 100% efficiency to below the noise floor when blanked. The detector gain can safely be increased while blanking the most intense mass lines simultaneously, thus improving the detection limit. The LoD of LMS-GT prior to the installation of the mass-selective blanking device was at ppm level (at. frac.) with few sub-ppm detections, the installation pushed it to the lower ppb range, without compromising the initial performance. This emphasises that fs-LIMS can be a powerful quantitative technique for the chemical analysis of solids, with the potential to reach the levels of mass spectrometric analysis achievable with Secondary Ion Mass Spectrometry (SIMS) and Laser Ablation–Inductively Coupled Plasma–Mass Spectrometry (LA-ICP-MS).

Accuracy requirements of the microarrayed Einzel lens

A microarrayed Einzel lens (MAEL) is adopted in many high throughput applications, such as multibeam lithography, multibeam electron microscope, and multibeam electron beam inspection. The assembly and fabrication errors of mounting an MAEL consist of misalignment, tilt, and ellipticity, which strongly affect the property of the MAEL. In this report, the accuracy requirements of mounting an MAEL are analyzed using Munro’s electron beam software. The results show that the assembly errors of the middle electrode in an MAEL are dominant in spoiling the beam quality. When assembling an MAEL, for a probe size of 10 nm, the requirements on misalignment, tilt, and ellipticity are 2.7 μm, 1 mrad, and 60 nm, respectively, while for a probe size of 1 nm, the assembly accuracy should be controlled to be less than 0.8 μm, 0.7 mrad, and 6 nm, respectively. These calculated results could be able to instruct designing an MAEL. Moreover, a dedicated tool is necessary for assembling the MAEL to ensure that the accuracy requirements of the MAEL are acceptable, to make good quality electron probes.

A photoionized pulsed low-energy ion beam source for quantum state-to-state crossed ion-molecule scattering.

Here, we report the designand test of a pulsed low-energy ion beam source for crossed ion-molecule scattering studies. The ions are produced by laser photoionization based methods and thus can be prepared in well-defined quantum states. By using the combination of a double Einzel lenses setup and a specially designed shielding tube, a well spatially confined ion bunch with tunable kinetic energies in the range of 1.0-5.0eV and typical spreads of ∼150meV (full width at half maximum) can be formed in the center of a velocity-map imaging (VMI) stack. By combining it with a recently constructed three-dimensional VMI system, the present apparatus is readily available for quantum state-to-state crossed ion-molecule scattering studies.

Design of an Einzel Lens with Square Cross-Section

In this paper, the results of modeling and simulation of a microcolumn are presented. The microcolumn is part of a developed miniature MEMS electron microscope equipped with a miniature MEMS high-vacuum micropump. Such an arrangement makes this device the first stand-alone miniature electron-optical device to operate without an external high-vacuum chamber. Before such a device can be fabricated, research on particular elements must be carried out to determine the working principles of the device. The results of the calculations described in this article help us to understand the work of a microcolumn with square holes in the electrodes. The formation of an electron beam spot at the anode is discussed. Further calculations and results show the dependence of the Einzel lens size on the electron beam spot diameter, electron beam current, and microcolumn focusing voltage. The results are used to define the optimal design of the developed MEMS electron microscope.

Raman Scattering Study on the Influence of E-Beam Bombardment on Si Electron Lens.

Microcolumns have a stacked structure composed of an electron emitter, electron lens (source lens), einzel lens, and a deflector manufactured using a micro electro-mechanical system process. The electrons emitted from the tungsten field emitter mostly pass through the aperture holes. However, other electrons fail to pass through because of collisions around the aperture hole. We used Raman scattering measurements and X-ray photoelectron spectroscopy analyses to investigate the influence of electron beam bombardment on a Si electron lens irradiated by acceleration voltages of 0, 20, and 30 keV. We confirmed that the crystallinity was degraded, and carbon-related contamination was detected at the surface and edge of the aperture hole of the Si electron lens after electron bombardment for 24 h. Carbon-related contamination on the surface of the Si electron lens was verified by analyzing the Raman spectra of the carbon-deposited Si substrate using DC sputtering and a carbon rod sample. We report the crystallinity and the origin of the carbon-related contamination of electron Si lenses after electron beam bombardment by non-destructive Raman scattering and XPS analysis methods.

Simulation Study for Beam Extraction with an Electrostatic Einzel Lens for Low Energy Accelerator Mass Spectrometry

Radiocarbon dating using a compact or low energy accelerator mass spectrometer has been rapidly developing in recent times. A gaseous ion source was designed and simulated to reduce sample preparation times. Then, a simulation study for low-energy accelerator mass spectrometry using the designed ion source for low energy beam transport was conducted to analyze beam separation optimization. Based on our simulation results, the use of an electrostatic Einzel lens led to an enhancement in beam focusing and separation. The ion beam trajectories were calculated using a SIMION program. These simulation results for ion beam extraction are presented in this paper.

Simulation and Optimization of the Optical Properties of an Einzel lens

The simulation and optimization calculations were carried out for an einzel lens consists of three overlap cylindrical electrodes with the same length but with different electrode diameters under point-to-point focusing condition. The effects of the overlap distance (d) between the central and the outer cylindrical electrodes on the optical properties of an einzel lens were investigated. The results showed that the increasing of the overlap distance (d) will improve the aberration figures of the images, where by increasing the overlap distance (d) from 2 mm to 6 mm the dimensions of the image were reduced by about 50% for both y and z-directions. The results appeared that both the dimensions of the lens, and the aberrations can be reduced at the same time without affecting the homogeneous distribution of an electron-beam kinetic energy of at the image plane.

Design and simulation of the parameters affecting the ion beam characteristics from a penning ion source

Today, many different kinds of ion sources have been developed. One of the most important ones is the penning or PIG ion source. Due to its simplicity of structure and longer lifetime, these ion sources are more widely considered than other ones. In this paper, design and simulation of the parameters affecting the ion beam characteristics from a penning ion source are performed using the CST software. Among the various structures of the permanent magnet around the source, the circular arrangement is found to be better for the confinement of particles inside the source. The electric potential of the anode, the cathode and the extraction electrode are found to be 15+, -500 and -3000 Volt, respectively. The decelerator and accelerator electrodes are used as ion source extraction systems. In addition, in the beam transport systems, high efficiency focusing in Einzel lens is more than that of immersion lens.

The development of a hydrogen-helium dual-beam ion implanter

Multiple ion beam facilities are powerful tools to simulate the irradiation effects of neutrons on relevant nuclear materials. Since hydrogen and helium are often generated in neutron irradiated materials as transmutation products and they play important roles in the defect evolution, the triple beam accelerator and transmission electron microscope link in situ facility instead of a monobeam or dual-beam facility is necessary to simulate neutron irradiation. A hydrogen-helium dual-beam ion implanter has been developed for a triple ion beam in situ facility at Xiamen University. A Penning ion source has been developed to produce H2 + and He+ simultaneously. A special system consisting of two Wien filters and an Einzel lens has been proposed to purify the species from a single Penning source and allow for the measurement of the He+/H2 + ratio, without disturbing the accelerator settings. The detail of this dual-beam ion implanter will be introduced in detail.

Status of the gasdynamic ion source for multipurpose operation (GISMO) development at IAP RAS.

A new experimental facility named GISMO (Gasdynamic Ion Source for Multipurpose Operation) was constructed at the IAP RAS to continue investigations in the field of gasdynamic ion sources. The source utilizes 28 GHz/10 kW gyrotron radiation for heating magnetically confined plasma. Magnetic field configuration provided by a fully permanent magnet system is much like a simple mirror trap. The GISMO source is aimed at the production of bright ion beams with hundreds of milliamperes current. The facility has been tested for continuous-wave (CW) operation with 2 kW of heating power to check durability of a microwave injection system and the plasma chamber. A 2-electrode extraction system with an integrated Einzel lens was designed for a formation of CW high current beam with up to 100 kV accelerating voltage. The first results on ion beam production at GISMO are presented together with the general progress status of the facility.