Ion Optics Research Articles

Design of a prototype thermal ionization cavity source intended for isotope ratio analysis

The design of a prototype thermal ionization cavity (TIC) source attached to the mass analyser of a MAT262 thermal ionization mass spectrometer is presented. In addition to a detailed calculation and experimental verification of the ion optics, the new design includes several innovative features that set it apart from previously reported TIC sources. The goal is to employ this new ion source for high-efficiency isotope ratio analysis.For uranium adsorbed to a single resin bead, an overall efficiency gain of about a factor of 10 compared to the same sample type analysed by state-of-the-art conventional thermal ionization mass spectrometry (TIMS) on a Triton instrument is reported (ions detected per atom loaded). First attempts at isotope ratio analysis of micrometre sized uranium oxide particles, as is commonly done for nuclear safeguards, seem to confirm the enhancement in overall efficiency and could help with the analysis of the minor uranium isotopes on such samples.

Development of an ion guide device in orthogonal acceleration time-of-flight mass spectrometer coupled with laser resonance ionization source

Laser-resonance-ionization time-of-flight mass spectrometer (LRI-TOF-MS) has been widely used in the analysis of trace isotopes because of its advantages such as high isotope selectivity, high sensitivity, and capability to receive all isotopes in a single measurement. A LRI-TOF-MS was built in our laboratory to search for efficient laser resonance ionization scheme of some elements and analyse their isotopic composition. To improve the resolution and suppress the peak tail, the orthogonal-acceleration technology was used in LRI-TOF-MS for the first time, and the design method of electrical parameters of TOF mass analyser with dual-stage reflectrons was derived. The developed ion guide device consisted of several different electrostatic lenses and was manufactured through theoretical analysis, SIMION simulation and experimental evaluation. The results show that the LRI source and the TOF mass analyser matched well in performance.

Muon Profile Measurement After Acceleration With a Radio-Frequency Quadrupole linac

We have measured the muon beam profile after acceleration using a radio frequency quadrupole linac (RFQ). Positive muons are injected to an aluminum degrader and negative muoniums (Mu−) are generated. The generated Mu−’s are extracted by an electrostatic lens and accelerated to 89 keV by the RFQ. The accelerated Mu−’s are transported to a beam profile monitor (BPM) through a quadrupole magnet pair and a bending magnet. The BPM consists of a micro-channel plate, a phosphor screen, and a CCD camera. The measured profile in the vertical direction is consistent with the simulation. This profile measurement is one of the milestones for realizing a muon linac for measurement of the muon anomalous magnetic moment at the Japan Proton Accelerator Research Complex.

A low energy ion beamline for TwinEBIS

A low energy beamline has been designed for the TwinEBIS setup. The beamline will be used to transport ions extracted from the electron beam ion source into an accelerating radio frequency quadrupole or into secondary devices, like a time of flight-mass spectrometer, attached to the beamline via a fast three way 20̂ ion switchyard. Optional injection of ions from an external source into the electron beam ion source is foreseen. In this article the general layout of the beamline is presented and supported with simulations of the ion-optical matching. Furthermore, the switchyard and gridded electrostatic lenses, chosen as the main focusing elements, have been simulated to assess their impact on the beam quality and the dynamics of secondary electrons emitted by the gridded lenses. In addition, the beamline includes general diagnostic devices, including a bidirectional pepperpot beam profiler. An overview of the diagnostic elements is given.

Integrable Trotterization: Local Conservation Laws and Boundary Driving.

We discuss a general procedure to construct an integrable real-time Trotterization of interacting lattice models. As an illustrative example, we consider a spin-1/2 chain, with continuous time dynamics described by the isotropic (XXX) Heisenberg Hamiltonian. For periodic boundary conditions, local conservation laws are derived from an inhomogeneous transfer matrix, and a boost operator is constructed. In the continuous time limit, these local charges reduce to the known integrals of motion of the Heisenberg chain. In a simple Kraus representation, we also examine the nonequilibrium setting, where our integrable cellular automaton is driven by stochastic processes at the boundaries. We show explicitly how an exact nonequilibrium steady-state density matrix can be written in terms of a staggered matrix product ansatz, and we propose quasilocal conservation laws for the model with periodic boundary conditions. This simple Trotterization scheme, in particular in the open system framework, could prove to be a useful tool for experimental simulations of the lattice models in terms of trapped ion and atom optics setups.

A Prism Mass-Spectrometer for Isotope Analysis of Hydrogen–Helium Mixtures

An original scheme of a special magnetic mass-spectrometer for isotope measurements in a mass range of hydrogen–helium mixtures and their main impurities is proposed. The ion optics system contains a two-dimensional magnetic prism supplemented with two identical cylindrical electrostatic capacitors matched so that the system operates in the regime of complete triple focusing of the ion beam in two orthogonal directions and with respect to ion energies. The system ensures high dispersion and allows the mass resolution (no less than 3500) required for analysis at high brightness and a central ion trajectory length on the order of 1 m.

DRILL Interface Makes Ion Soft Landing Broadly Accessible for Energy Science and Applications.

Polyoxometalates (POM) have been deposited onto carbon nanotube (CNT) electrodes using benchtop ion soft landing (SL) enabled by a vortex-confined electrohydrodynamic desolvation process. The device is based on the dry ion localization and locomotion (DRILL) mass spectrometry interface of Fedorov and co-workers. By adding electrospray emitters, heating the desolvation gas, and operating at high gas flow rates, it is possible to obtain stable ion currents up to -15 nA that are ideal for deposition. Coupled with ambient ion optics, this interface enables desolvated ions to be delivered to surfaces while excluding solvent and counterions. Electron microscopy of surfaces prepared using the device reveal discrete POM and no aggregation that degrades electrode performance. Characterization of POM-coated CNT electrodes in a supercapacitor showed an energy storage capacity similar to that achieved with SL in vacuum. For solutions that produce primarily a single ion by electrospray ionization, benchtop SL offers a simpler and less costly approach for surface modification with applications in catalysis, energy storage, and beyond.

Improved ion optics for low energy neutral atom imaging with high sensitivity

An ion-optical system suitable for imaging neutral atom fluxes with energies <∼1 keV has been developed by means of computer simulations. Although conceptually similar to the IBEX-Lo sensor flown on the interstellar boundary explorer mission “IBEX”, the new ion optics presented here exhibits up to 29-fold higher sensitivity with similar angular resolution. This improvement is achieved through a substantial increase in the geometric factor and ion collection–transmission following conversion to negative ions. Energy resolution can be dynamically adjusted during operations by changing a single electrode voltage.

An Rf-only ion funnel interface for ion cooling in laser ablation time of flight mass spectrometry

In this work we describe a novel concept for an efficient ion extraction for laser ablation time-of-flight mass spectrometry. The concept combines a sample, placed in a chamber filled with a helium buffer gas, a conventional converging-diverging supersonic nozzle connected to this chamber at short distance behind the sample, an electrodynamic Rf-only ion funnel placed on the nozzle axis in immediate vicinity of the nozzle exit plane and a pulsed laser source (frequency-doubled Nd:YAG, 532 nm, 3 ns pulse duration; 7.6 × 108 W power, 10 Hz repetition rate), focused onto the sample surface to a spot diameter of 110 μm after passing through the funnel and the supersonic nozzle.The primary hot ions generated during ablation are cooled by collisions with buffer gas, accelerated into the subsonic converging part of the nozzle and finally transported through the supersonic diverging part of the nozzle into the Rf-only funnel via gas expansion. Inside funnel ions are again cooled and focused by the converging electrodes and the applied RF field towards the high vacuum stage containing the ion optics and mass analyzer.To evaluate the performance of the instrument, parametric studies were carried out. It was found that ion transmission is strongly dependent on the applied RF amplitude and frequency as well as the buffer gas pressure in the ablation region and funnel chamber. The present configuration achieves an integrated sensitivity approximately 2 orders of magnitude higher than when the ablation is carried out under high-vacuum conditions with the sample placed at the position of the ion funnel exit. The new ion guide leads to significantly longer duration of ion signals from a single laser pulse and thereby would also alleviate space charge effects. The signal profile is mostly dependent on pressure conditions in the ion source. To some extent it is also affected by the RF-operating conditions of the ion funnel. Optimizing for high transmission of low m/Q ions caused an intermediate suppression of ion signals of high m/Q isotopes and vice versa. Because the respective suppression is highest during the peak maximum of the highly abundant ions, this behavior is attributed to exceeding the space charge limit inside the ion funnel for high total ion currents. Furthermore, cluster ion abundancies and their transmission were characterized. Molecular oxide ions and water clusters were found to be the dominating molecular ions in this study. Their formation generally increased with buffer gas pressure in the ablation chamber, while otherwise transmission through the ion funnel was similarly affected by the ion funnel operation as by atomic ions of similar m/Q. Relative sensitivity coefficients were found to be generally comparable when analyzing standard reference materials of similar matrix composition with laser ablation using a wavelength of 532 nm, nanosecond laser.

Differential algebraic description for aberrations analysis of typical electrostatic einzel lens

In the present paper the modern map method has been used to calculate the third-fifth order geometric aberration, the first-third order chromatic aberration and the Gaussian optical properties for Schiske’s and inverse Schiske’s electrostatic lenses. COSY INFINITY 10 program is used for the aberration analysis and calculation of properties of electrostatic electron lenses. The Numerical results show that the differential algebraic method is an excellent method with high accuracy for calculating the high order electron optical aberration analysis.

Optimization of the Radiation Resistant Quadrupole Magnets for the SIS100 Accelerator of the FAIR Project

The SIS100 is a charged particle accelerator developed as a part of the challenging international project Facility for Anti-proton and Ion Research taking place in Darmstadt, Germany. The ion optics of the SIS100 accelerator includes superconducting and normal conducting quadrupole magnets. To fulfill the requirements of the field quality in the magnet aperture, it is necessary to find an optimal pole tip shape as well as an optimal configuration of the coil system. Requirements for radiation resistant magnets installed in the extraction section of the SIS100 accelerator combine high quality of the field distribution, maximum field intensity at the pole tip of more than 1.3 T, and a wide range of the flux density variation. We used a specially developed optimization procedure for designing the magnet cross section. The pole border line is described by a superposition of hyperbolic functions corresponding to different Fourier components of the magnetic field expansion. Strong correlation between amplitudes of the pole shape and field harmonics enables high performance of the optimization algorithms. The developed procedures have been used for designing a quadrupole magnet with especially wide range of the flux density variation. Integral 3-D properties of the developed quadrupoles were ensured by optimization of the magnet end chamfers.

24-channel dual microcontroller-based voltage controller for ion optics remote control

The design of a 24-channel voltage control instrument for Wenzel Elektronik N1130 NIM modules is described. This instrument is remote controlled from a LabVIEW GUI on a host Windows computer and is intended for ion optics control in electron affinity measurements on negative ions at the CERN-ISOLDE facility. Each channel has a resolution of 12 bits and has a normally distributed noise with a standard deviation of <1 mV. The instrument is designed as a standard 2-unit NIM module where the electronic hardware consists of a printed circuit board with two asynchronously operating microcontrollers.

A horizontal multi-purpose microbeam system

A horizontal multi-purpose microbeam system with a single electrostatic quadruplet focusing lens has been developed at the Columbia University Radiological Research Accelerator Facility (RARAF). It is coupled with the RARAF 5.5 MV Singleton accelerator (High Voltage Engineering Europa, the Netherlands) and provides micrometer-size beam for single cell irradiation experiments. It is also used as the primary beam for a neutron microbeam and microPIXE (particle induced x-ray emission) experiment because of its high particle fluence. The optimization of this microbeam has been investigated with ray tracing simulations and the beam spot size has been verified by different measurements.

High spatial resolution and high brightness ion beam probe for in-situ elemental and isotopic analysis

A high spatial resolution and high brightness ion beam from a cold cathode duoplasmatron source and primary ion optics are presented and applied to in-situ analysis of micro-scale geological material with complex structural and chemical features. The magnetic field in the source as well as the influence of relative permeability of magnetic materials on source performance was simulated using COMSOL to confirm the magnetic field strength of the source. Based on SIMION simulation, a high brightness and high spatial resolution negative ion optical system has been developed to achieve Critical (Gaussian) illumination mode. The ion source and primary column are installed on a new Time-of-Flight secondary ion mass spectrometer for analysis of geological samples. The diameter of the ion beam was measured by the knife-edge method and a scanning electron microscope (SEM). Results show that an O2- beam of ca. 5 µm diameter with a beam intensity of ∼5 nA and an O- beam of ca. 5 µm diameter with a beam intensity of ∼50 nA were obtained, respectively. This design will open new possibilities for in-situ elemental and isotopic analysis in geological studies.

Charge accumulation in electron cryomicroscopy

When irradiated in a transmission electron microscope, plunge-frozen, amorphous water ice specimens accumulate a pattern of static charge that changes dynamically as the specimen is irradiated, and which can deflect the transmitted electrons and blur the resultant micrographs. Here we provide a physical description of this charge accumulation and characterise its dynamic behaviour in the context of low-dose electron cryomicroscopy (cryoEM). We observe the accumulation of positive charge in the primary irradiation area as expected from earlier work. To our surprise, we also observed a build-up of negative charge in nearby unirradiated regions of the specimen. Using a standard carbon support foil containing a pure water ice specimen, we collect a portion of this negative charge in the micrometer sized specimen holes which act as electrostatic lenses. These unusual, diverging micro-lenses are extremely sensitive charge detectors that allow us to directly measure the magnitude and dynamics of charge accumulation and neutralisation that occur during cryoEM imaging. Using these measurements, we find that the build-up of charge on the specimen saturates to a dynamic equilibrium at an electron fluence which is orders of magnitude lower than required for a typical low-dose micrograph. The measurements here will guide the development of optimal imaging conditions for biological specimens and contribute to a complete theory of information loss in electron cryomicroscopy.

Spatial rainbows and catastrophes in transmission of protons through electrostatic octopole lens

This paper considers transmission of initial parallel proton beam with kinetic energy of 10 k?V through electrostatic octopole lens. The spatial rainbows and corresponding proton distributions are calculated by using infinite length approximation potential. Positive potentials of the lens electrodes are set to be 0.35 kV and 9 kV. It has been shown that by application of catastrophe theory, generating function for mapping proton positions between entrance and exit transverse plains can be determined, giving accurate rainbow patterns for biasing potentials of 0,35 kV.

Micropatterning by electrospray deposition (ESD) with an electrostatic lens

Micropatterning by electrospray deposition (ESD) with an electrostatic lens

Spatial rainbows and catastrophes in transmission of protons through electrostatic hexapole lens

This work reports on the spatial rainbows occurring in transmission of 10 keV protons through hexapole lens. Positive potentials of the lens electrodes are set to be 0.9, 2, and 5 kV. The spatial rainbows and corresponding proton distributions are calculated by using an accurate analytical approximation of the numerically obtained lens potential. Further, for the positive potential of the lens electrode equal to 0.9 kV, it has been shown that application of catastrophe theory leads to a simple polynomial non-linear mapping, generating accurate spatial rainbows at the exit and in the drift space behind the lens.

Development of a compact FE-SEM and X-ray microscope with a carbon nanotube electron source

A carbon nanotube (CNT) possesses various benefits as a field electron emitter. Multi-walled CNT (MWNT) have exhibited high brightness and the field emission (FE) current is stable even under poor high-vacuum condition of 10−6 – 10−7 Pa without ion pumping. In this study, we have experimentally manufactured a compact composite field emission scanning electron microscope (FE-SEM) and X-ray microscope (XRM) with a single isolated MWNT electron source. An electron beam from a MWNT was focussed and accelerated by a Butler electrostatic lens. Stable SEM images were observed at a Butler voltage Vbut = 1.5 kV and accelerating voltage Vacc ≃ 15 kV with a focussed probe current Ifoc = 61 pA. The spatial resolution of the SEM, which was estimated from 80 – 20 % edge profile of polystyrene latex spheres, was about 9 nm. XRM images were acquired by 30-min exposure at Vbut = 1.5 kV and Vacc ≃ 17 kV. A spatial resolution of about 200 nm was obtained for XRM. The present results prove the high performance of the compact FE-SEM and XRM using a single isolated MWNT electron source at 10–7 Pa.

Numerical simulation of full-aperture-pair ion optics in a miniature ion thruster

The 211-aperture-pair two-grid ion optics of a miniature ion thruster is numerically simulated. Since the plasma in the miniature ion thruster is too inhomogeneous to introduce mirror or translational boundary conditions between apertures, all the apertures of the grid system are considered. The simulation is self-consistent, the ion current profile in the discharge chamber plasma is given by the particle-in-cell with Monte Carlo collision algorithm calculations, and all the ion beams extracted from the full-aperture-pair array were tracked including charge-exchange ions. A scheme for the construction of the full-aperture-pair simulation domain is proposed based on the array of a six-fold hexagonal single-aperture-pair simulation domain, which can be extended to other numbers of aperture pairs. Numerical results on accel impingement current and ion-beam profile are compared to experimental data and shown to be in reasonable agreement. Furthermore, the full-aperture-pair ion-optics model is compared with the single-aperture-pair ion-optics models used in the majority of previous ion-optics simulations, which showed that the full-aperture-pair ion-optics model yielded the most accurate predictions. These results suggest that the ion thruster grid system using an inhomogeneous plasma source can be designed more accurately and effectively using full-aperture-pair ion-optics simulations.