Wien Filter Research Articles

Writing with Mass-Selected Ions Using a Dynamic Field Wien Filter.

We have designed and constructed a low-cost Wien filter based on strong permanent magnets and integrated it into an ion soft-landing instrument to enable parallel deposition as well as one- and two-dimensional surface patterning of mass-selected ions using dynamic fields. We show the capabilities of this device for separating ions from a multicomponent high-flux continuous ion beam and simultaneous deposition of ions of different mass-to-charge ratios onto discrete locations on a surface. When a dynamic electric field is applied parallel to the magnetic field, ions are deposited in one-dimensional arrays, laterally separated by mass. The field's strength, frequency, and waveform type determine both the lengths of the arrays and the density of ions across the 1-D pattern. Additionally, a second dynamic field from user-defined waveforms orthogonal to the magnetic field enables two-dimensional surface patterning of ions while maintaining mass separation. These experiments demonstrate the practical utility of a Wien filter for the controlled fabrication of interfaces with arbitrary patterns of mass-selected ions.

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.

Development of a 50kV hydrogen-helium mixed ion beam implanter.

Ion implanters have extensively been employed to simulate the irradiation effects of neutrons on relevant nuclear materials. In this study, a 50kV hydrogen-helium mixed ion beam implanter was developed to generate H2+ and He+ ion beams, with a beam current of 20 µA, while keeping the impurity ion content below 2%. The ions are generated by an antenna-type 2.45GHz electron cyclotron resonance ion source, and the hydrogen-to-helium ion beam ratio was controlled using two gas mass flow controllers to ensure long time stability of the beam current. As a result, the H2+/He+ ratio, beam size, and homogeneity of the beam spot can be maintained at a stable level. The beam line consisted of four Wien filters, a movable dual-slit plate, and an accelerator tube. The experimental results demonstrated successful transport of more than 20 µA of H2+ and He+ ion beams onto the target, with a beam axis deviation of less than 0.5mm.

Performance and plasma diagnostics of the Air-breathing Microwave Plasma CAThode (AMPCAT) coupled to a cylindrical Hall thruster

The Air-breathing Microwave Plasma CAThode (AMPCAT) has been developed for air-breathing electric propulsion in very-low Earth orbit. In this study, the standalone AMPCAT plasma characteristics are analyzed by means of several diagnostic tools and operation on xenon is compared to a conventional hollow cathode. A transition of AMPCAT extracted current from a lower (<0.1 A) to higher-current (>0.5 A) mode, triggered by increasing the negative cathode bias voltage, is accompanied by a significant rise in internal electron density and external electron temperature. The AMPCAT is coupled with a cylindrical Hall thruster in the 100–300 W power-level running on 0.5–0.7 mg/s of xenon, and the thrust is directly measured for cathode operation with both xenon and air. Stable thruster operation is demonstrated for the AMPCAT running on both propellants. For xenon, the performance is compared to a hollow cathode, which reveals matching discharge current profiles but a significantly higher thrust for the AMPCAT at low discharge voltages, approximately two times higher at 200 V. Langmuir probe measurements highlight a 30–40 V lower plasma potential in the cathode vicinity for the AMPCAT with xenon compared to both the hollow cathode and AMPCAT with air. This indicates a significantly improved coupling of cathode electrons to the thruster discharge, yielding an increased degree of ionization. Faraday probe and Wien filter results show that a larger current utilization efficiency drives the observed performance difference at low discharge voltages, rather than a significant change in ion acceleration or plume divergence.

Focused ion beams from GaBiLi liquid metal alloy ion sources for nanofabrication and ion imaging

In this work, we present an overview of nanopatterning and imaging applications using newly developed workflows with focused ion beams (FIBs) produced with a GaBiLi liquid metal alloy ion source. The primary beam of this source type contains gallium, bismuth, and lithium as well as cluster ions which can be separated quickly using a Wien filter. Lithium ion milling has been applied to generate heptamer-arranged nanohole arrays in gold films with high resolution. Workflows for two-step bowtie nanofabrication using lithium and bismuth ions from the same source have been established. Furthermore, we present ion beam imaging results that were obtained with lithium ions on various sample materials. Combining the large sputter yield and high depth resolution of heavy bismuth ions with the high lateral imaging resolution of light lithium ions enables 3D nanoscale tomography using different ion species generated from the same source. Sample tilt is not required due to the top-down geometry of the FIB.

Quantum wave function reconstruction by free-electron spectral shearing interferometry.

The quantum wave function measurement of a free electron remains challenging in quantum mechanics and is subject to disputes about ψ-ontic/epistemic interpretations of the wave function. Here, we theoretically propose a realistic spectral method for reconstructing quantum wave function of an electron pulse, free-electron spectral shearing interferometry (FESSI). We use a Wien filter to generate two time-delayed replicas of the electron wave packet and then shift one replica in energy using a light-electron modulator driven by a mid-infrared laser. As a direct demonstration, we numerically reconstruct a pulsed electron wave function with a kinetic energy of 10 keV. FESSI is experimentally feasible and enables us to fully determine distinct orders of spectral phases and their physical implications in quantum foundations and quantum technologies, providing a universal approach to characterize ultrashort electron pulses.

Developments at the CERN-ISOLDE Offline 2 mass separator

The Offline 2 mass separator laboratory is part of the CERN-ISOLDE Offline facilities - a suite of installations required to perform essential quality control on target and ion source units before irradiation at CERN-ISOLDE (Catherall et al., 2017) [1]. The facility is also used for extended preparatory offline studies as a prerequisite before conducting any beam development on-line, especially establishing systematic effects. The Offline 2 separator resembles the on-line CERN-ISOLDE Frontend and employs identical services such as beam instrumentation, gas delivery system, laser ionization and the equipment control system. The facility is able to generate dc as well as bunched non-radioactive beams up to an energy of 60keV. The mass resolving power of the existing 90° dipole mass separator magnet is R≈500 (Warren et al., 2020) [2]. The ion beams can be cooled and bunched in an unmodulated RFQ. In order to study effects of the RFQ buffer gas on the formation of molecular species, a dedicated identification setup is required. We intend to employ a Wien filter downstream the RFQ. This work presents initial beam dynamics simulations through the entire Offline 2 facility to prepare injection into the RFQ. The fields of the RFQ are also shown serving as a basis for field map PIC simulations. Furthermore, we present the status of the emittance meter preparations in front of the separator magnet allowing a comparison to the beam dynamics simulations.

KoBRA Wien filter for low-energy RI beam production and recoil separation

The Wien filter is one of the key components in ion optics to improve the mass separation performance. The KoBRA Wien filter will be installed at the low-energy beamline KoBRA of RAON in Korea. The specifications of the KoBRA Wien filter were determined based on the ion beams expected in the KoBRA beamline, especially, beam energies less than about 5 MeV/nucleon suitable for nuclear astrophysics experiments. The Wien filter is designed to have the maximum field intensities of 0.2 T for the magnetic field and 2.0 kV/mm for the electric field in the ±75(H)×±50(V)×2500(L)mm3 good-field region. Performance of the Wien filter was estimated by the ion optics calculations of the KoBRA beamline for 40Ar beams at 18.5 MeV/nucleon and 14O beams at 2.5 MeV/nucleon. The mass resolving powers are 42.65 and 517, respectively. Currently, the KoBRA Wien filter is being manufactured, and will perform a factory acceptance test.

Experimental and numerical studies of low power Hall thruster performance

The low power Hall thruster has the potential to be applied in multiple apace missions. In order to study the performance of the low power Hall thruster, a 200W-class Hall thruster is designed and manufactured. The plasma properties in the discharge channel are investigated via numerical simulation. The ionic composition and ion current density are respectively measured by a Wien filter and a Faraday probe. The generated thrust is measured by a thrust target. The simulation results show that the maximal ion number density is more than 1×1018 m-3. The ionization and acceleration regions are located in the midstream and downstream of the discharge channel. The experimental results reveal that thrust, anode specific impulse and anode efficiency are 12.13 mN, 1380 s, and 41% at 200 W. The ion current density decreases along the radial direction. According to the results of simulation and experiment, the thruster is reasonable and feasible. Our research provides a reference for the design of low power Hall thruster. Structural optimization and performance improvement will be carried out further.

RETRACTED: Quasi-frozen spin concept of magneto-optical structure of NICA adapted to study the electric dipole moment of the deuteron and to search for the axion

The “frozen spin” method is based on the idea that at certain parameters of the ring, the particle spin rotates with the frequency of the momentum, creating conditions for the continuous growth of the electric dipole moment signal. The Nuclotron-based Ion Collider fAcility (NICA) is under construction in Joint Institute for Nuclear Research [1]. Since a straightforward implementation of the frozen spin regime at NICA is impossible, we suggest an alternative “quasi-frozen spin” concept. In this new regime, the reference particle’s spin-vector precesses with a spin phase advance π ⋅ γG/2 per beam revolution, locally recovering the longitudinal orientation at the location of the electric-magnetic elements, Wien filters, placed in the straight sections. In the deuterons case, thanks to the small magnetic anomaly G, the spin-vector continuously oscillates relative to the direction of the momentum-vector with a small amplitude of a few degrees and the expected EDM effect is reduced only by a few percent. In this paper, we study the spin-orbital motion with the aim of using the NICA collider to measure the EDM. We also comment on the potential of NICA as an axion antenna in both the quasi-frozen spin regime and beyond.

Backgrounds and blanks in Iodine-129 measurements at the Australian National University

The molecular hydride negative ions of mass 129 amu, 127IH2−, 127ID− and 128TeH−, have been studied in order better to understand potential backgrounds in AMS measurements of 129I. All three of these ions appear to be stable or, if metastable, to have lifetimes that are sufficiently long to allow at least some of them to reach the high voltage terminal of the accelerator. It is found, however, that these make only a minor contribution to the combined rate of 127I7+ and 128Te7+ ions that pass around the analysing magnet when it is set for 129I7+ detection. The principal contribution comes instead from the injection of 127I− ions into the accelerator along with the 129I− ions, despite the use of a low Cs sputtering energy in the ion source that was intended to eliminate them. This contribution is, however, small and is effectively removed by a Wien filter. In addition, a sample of Woodward iodine, obtained from the University of Arizona, was found to have an 129I/127I ratio of (13.3 ± 0.9) × 10−15. This is the lowest ratio so far reported. In contrast, the batch of Woodward iodine that was being used as an iodine carrier in our laboratory was found to have a much higher ratio of (78.2 ± 2.4) × 10−15. A search for a lower ratio blank failed to find a suitable material.

Design study for large acceptance muon beamlines by using beam splitting methods

A muon beamline scheme is designed for the Phase-I of the Experimental Muon Source (EMuS), which is a standalone facility by sharing the proton beam extracted from the Rapid Cycling Synchrotron (RCS) of China Spallation Neutron Source (CSNS). The proton beam for EMuS has a beam power of 20–25 kW and kinetic energy of 1.6 GeV with a low repetition rate of 1.25–2.5 Hz. Different from traditional muon beamline design, a sophisticated beam splitting system using combined spatial and time splitting methods has been developed for the EMuS beamline. In order to profit a graphite target of long effective length, the beamline is designed to have a large horizontal acceptance of 6000π·mm·mrad. A special electrostatic deflector with two channels splits the beam spatially into two branch beamlines, so that the reduced horizontal emittance of the split beams becomes utilizable for applications. Since the muon beam has a time structure of two bunches per pulse that inherits from the proton beam and a single bunch is required for μSR applications, a fast kicker magnet is used to separate two bunches into two endstations. All these make simultaneous muon beams in four endstations that are basically for μSR applications. Surface muons with an intensity order of 105/s and different spot sizes are available for all the four endstations. The contaminated positrons are carefully treated to reduce the background by combining the use of the electrostatic deflector and a dedicated Wien filter.

Combined electrostatic analyzer—Wien filter probe for characterization of species distributions in Hall thrusters

We present a combined electrostatic and magnetostatic plasma diagnostic tool used to measure current fractions of ion species in a Hall-effect thruster plume. Hall thrusters produce thrust by accelerating singly and multiply charged ions to high velocity. Singly charged ions fall through potential differences from their point of creation to the location of measurement, which varies as a function of time and position resulting in a relatively wide distribution of energy. This process is further complicated by both direct and multi-step creation of multiply charged ions and by ion-neutral collisions. The result is that Wien velocity filter (ExB) spectra typically have overlapping peaks. Analysis of these spectra requires assumptions about the velocity distribution function (VDF) that are hard to verify and can result in the incorrect species current distribution used to calculate thruster performance efficiencies. We present how adding an energy filter in line with an ExB probe can result in a more accurate measurement of the species current fraction while also providing information about the ion energy distribution of each species. The combined diagnostic was used to measure the species current distribution in a 1.5 kW Hall thruster operating on krypton. The diagnostic setup and data analysis of the probe measurements are presented and compared against results utilizing established VDF-fit and integration techniques applied to standard spectra measured by a standalone ExB probe.

New method of probing an oscillating EDM induced by axionlike dark matter using an rf Wien filter in storage rings

A hypothetical pseudo-scalar particle axion, which is an immediate result of the Peccei-Quinn solution to the strong CP problem, may couple to gluons and lead to an oscillating electric dipole moment (EDM) of fundamental particles. This paper proposes a novel method of probing the axion-induced oscillating EDM in storage rings, using a radiofrequency (RF) Wien Filter. The Wien Filter at the frequency of the sidebands of the axion and $g-2$ frequency, $f_\text{axion} \pm f_{g-2}$, generates a spin resonance in the presence of an oscillating EDM, as confirmed both by an analytical estimation of the spin equations and independently by simulation. A brief systematic study also shows that this method is unlikely to be limited by Wien Filter misalignment issues.

High Voltage Design and Evaluation of Wien Filters for the CEBAF 200 keV Injector Upgrade

High Voltage Design and Evaluation of Wien Filters for the CEBAF 200 keV Injector Upgrade

Plasma Plume Characterization of a 100 kW Nested Hall Thruster

The plasma plume properties of a three-channel 100-kW-class nested Hall thruster were measured on xenon propellant for total powers up to 80 kW. The thruster was throttled through all seven available channel combinations for conditions spanning 300 to 500 V discharge voltage and three discharge current densities. A plasma diagnostics array, which included a Wien filter spectrometer, a retarding potential analyzer, and a planar Langmuir probe, was placed in the far-field plume of the thruster and used to measure the beam ion charge state, the ion energy distribution function, and the local plasma potential. These data were used to calculate thruster phenomenological efficiencies. These efficiencies are compared across the discharge voltage and channel combination, and they are compared to similar results from the NASA-300M single-channel high-power Hall thruster. An estimate of cross-channel ingestion, which is a phenomenon in the nested configuration that may improve thruster efficiency and that will be present in space, is calculated, and the results for mass utilization efficiency are corrected for this effect. These plasma diagnostic results are discussed in the context of the state of the art, as well as in that of the viability and potential benefits of the nested channel thruster configuration.

Project Vienna: A Novel Precell Mass Filter for Collision/Reaction Cell MC-ICPMS/MS.

The last decade has seen widespread adoption of triple quadrupole-based inductively coupled plasma-tandem mass spectrometry (ICPMS/MS) technique using a collision/reaction cell in combination with a precell bandpass mass analyzer to measure isotopes otherwise masked by spectral interferences. High-precision isotope ratio analysis containing such isotopes would benefit from a similar capability on a multicollector inductively coupled plasma mass spectrometry (MC-ICPMS) platform, but using a quadrupole-based precell mass analyzer for MC-ICPMS/MS has several limitations. To overcome these limitations, we developed a novel precell mass analyzer for MC-ICPMS/MS using sector field technology. The new precell mass analyzer, comprising two Wien filters and a selection aperture, and a hexapole collision/reaction cell were integrated together in a single module and added to the commercially available Thermo Scientific Neptune XT MC-ICPMS to create a prototype MC-ICPMS/MS we named Vienna. Vienna was proven to retain the same performance of the base MC-ICPMS in terms of sensitivity, accuracy, and precision. Using the Vienna mass filter to eliminate Ar-based species, the abundance sensitivity achievable was equivalent to TIMS at mass 237.05, which was used to accurately determine the low 236U/238U isotope ratio of the uranium reference material IRMM184 (certified value, 1.2446 × 10-7). The performance of Vienna was then tested for a variety of geoscience applications that were expected to benefit from MC-ICPMS/MS technique, including Ca, K, Si, and in situ Rb/Sr dating by laser ablation.

Beam line design and beam transport calculation for the μSR facility at RAON

The Rare Isotope Science Project was launched in 2011 in Korea toward constructing the Rare isotope Accelerator complex for ON line experiments (RAON). RAON will house several experimental systems, including the Muon Spin Rotation/Relaxation/Resonance (μSR) facility in High Energy Experimental Building B. This facility will use 600-MeV protons with a maximum current of 660 pμA and beam power of 400 kW. The key μSR features will facilitate projects related to condensed-matter and nuclear physics. Typical experiments require a few million surface muons fully spin-polarized opposite to their momentum for application to small samples. Here, we describe the design of a muon transport beam line for delivering the requisite muon numbers and the electromagnetic-component specifications in the μSR facility. We determine the beam-line configuration via beam-optics calculations and the transmission efficiency via single-particle tracking simulations. The electromagnet properties, including fringe field effects, are applied for each component in the calculations. The designed surface-muon beamline is 17.3 m long, consisting of 2 solenoids, 2 dipoles affording 70° deflection, 9 quadrupoles, and a Wien filter to eliminate contaminant positrons. The average incident-muon flux and spin rotation angle are estimated as 5.2 × 106 μ+/s and 45°, respectively.

Data transmission by quantum matter wave modulation

Classical communication schemes exploiting wave modulation are the basis of our information era. Quantum information techniques with photons enable future secure data transfer in the dawn of decoding quantum computers. Here we demonstrate that also matter waves can be applied for secure data transfer. Our technique allows the transmission of a message by a quantum modulation of coherent electrons in a biprism interferometer. The data is encoded in the superposition state by a Wien filter introducing a longitudinal shift between separated matter wave packets. The transmission receiver is a delay line detector performing a dynamic contrast analysis of the fringe pattern. Our method relies on the Aharonov–Bohm effect but does not shift the phase. It is demonstrated that an eavesdropping attack will terminate the data transfer by disturbing the quantum state and introducing decoherence. Furthermore, we discuss the security limitations of the scheme due to the multi-particle aspect and propose the implementation of a key distribution protocol that can prevent active eavesdropping.

Beam Optics Design for the μSR Facility at the RAON Facility in Korea

The beam optics was evaluated to determine the specifications for the electromagnets in the proton beamline and the surface muon beamline at the RAON facility. Beam optics was evaluated, up to the fifth order by using GICOSY software; fringe field effects were also investigated. The distributions of the position and the angular divergence of 600-MeV protons were assumed to be Gaussian, and the initial beam emittance was 0.125 π mm mrad. The proton beamline was optimized by adjusting the positions and the magnetic fields of the electromagnetic components. The full width at half maximum (FWHM) proton beam size at the muon production target was 2.75 mm (x) × 6.73 mm (y), which met the requirement for achieving the maximum surface-muon production at the target. The designed surface-muon beamline is 23-m long and consists of two solenoids, two dipoles with a deflection angle of 70°, six quadrupoles, and a Wien filter. For an initial muon beam size of 6 cm (x) × 2 cm(y), the expected muon intensity at the end of the beamline, where the muon irradiation sample will be located, was estimated to be 7.7 × 107 per second.