Electron Beam Ion Trap Research Articles

Measurement of differential collisional excitation cross sections for the Kα emission of He-like oxygen

We measure the energy-differential cross sections for collisional excitation of the soft x-ray electric-dipole Kα (x+y+w) emission from He-like oxygen (O ), using an electron beam ion trap. Values near their excitation thresholds were extracted from the observed emissivity by rapidly cycling the energy of the exciting electron beam. This allows us to subtract time-dependent contributions of the forbidden z-line emission to the multiplet. We develop a time-dependent collisional-radiative model to further demonstrate the method and predict all spectral features. We then compare the extracted x+y+w cross sections with calculations based on distorted-wave and R-matrix methods from the literature and our own predictions using the . All R-matrix results are validated by our measurements of direct and resonant excitation, supporting the use of such state-of-the-art codes for astrophysical and plasma physics diagnostics. Published by the American Physical Society 2024

N = 3−3 lines in the extreme ultraviolet spectrum of europium (Z = 63)

Using high-resolution flat-field spectrographs at the LLNL SuperEBIT electron beam ion trap, we have observed extreme ultraviolet spectra (λ 32–43 Å) of highly charged ions of Eu ( Z = 63) under a range of production conditions suitable for Na- through Zn-like ions. Almost 30 lines were identified with the aid of Flexible Atomic Code computations and spectral modeling. While some of the wavelength measurements are among the most accurate in this wavelength range, some of the identifications are still tentative. We discuss how experimental conditions and spectral complexity interact in the analysis process.

Diffraction order penalization to improve spectrometer calibrations

Wavelength calibration in diffraction spectroscopy typically depends on identifying strong, well-known lines in the recorded spectra and fitting a calibration function to them. In this paper, we outline a novel method (order penalization) for improving spectroscopic calibrations by extending non-linear least squares fitting of the calibration curve. The method introduces an extra term into the minimized quantity that penalizes disagreement in the positions of spectral lines observed in multiple diffraction orders. The primary advantage of this method is that the lines used do not have to be identified, except for establishing the fact that they are different orders of the same line. This increases the number of constraints on the calibration curve, potentially in spectral regions where no regular calibration lines are available. The mathematical basis of this method is described, and the performance of this method is evaluated on simulated data and experimental data from the National Institute of Standards and Technology (NIST) Electron Beam Ion Trap. We demonstrate the effectiveness of the method on the spectra of highly charged Ag-like Re28+ and nearby charge state ions.

Development of an atomic spectra research platform based on a 30-keV electron beam ion trap.

Electron Beam Ion Traps (EBITs) serve as efficient tools for producing and studying highly charged ions. In response to the diagnostic requirements of upcoming magnetic confinement fusion devices, a medium-energy atomic spectra research platform based on a compact EBIT is developed. This platform achieves a central magnetic field of up to 1.0T, with electron beam currents reaching 20 mA and electron energies up to 30keV, similar to the electron temperature on fusion reactors. The developed atomic spectra platform successfully provided spectral data for elements such as argon, xenon, iron, and tungsten. This platform stands as a valuable asset for advancing research in nuclear fusion, particularly concerning impurity spectroscopic diagnostics.

Laboratory Benchmark of n ≥ 4 Dielectronic Recombination Satellites of Fe xvii

We calculated cross sections for the dielectronic recombination (DR) satellite lines of Fe xvii and benchmarked our predictions with experimental cross sections of Fe xvii resonances that were monoenergetically excited in an electron-beam ion trap. We extend the benchmark to all resolved DR and direct electron-impact excitation (DE) channels in the experimental data set, specifically the n ≥ 4 DR resonances of Fe xvii, complementing earlier investigations of n = 3 channels. Our predictions for the DR and DE absolute cross sections for the higher n complexes disagree considerably with experimental results when using the same methods as in previous works. However, we achieve agreement within ∼10% of the experimental results by an approach whereby we doubly convolve the predicted cross sections with both the spread of the electron-beam energy and the photon energy resolution of our experiment. We then calculated rate coefficients from the experimental and theoretical cross sections, finding general agreement within 2σ with the rates found in the OPEN-ADAS atomic database.

High-resolution laboratory measurements of M-shell Fe EUV line emission using EBIT-I

Solar physicists routinely utilize observations of Ar-like Fe IX and Cl-like Fe X emission to study a variety of solar structures. However, unidentified lines exist in the Fe IX and Fe X spectra, greatly impeding the spectroscopic diagnostic potential of these ions. Here, we present measurements using the Lawrence Livermore National Laboratory EBIT-I electron beam ion trap in the wavelength range 238–258 Å. These studies enable us to unambiguously identify the charge state associated with each of the observed lines. This wavelength range is of particular interest because it contains the Fe IX density diagnostic line ratio 241.74 Å/244.91 Å, which is predicted to be one of the best density diagnostics of the solar corona, as well as the Fe X 257.26 Å magnetic-field-induced transition. We compare our measurements to the Fe IX and Fe X lines tabulated in CHIANTI v10.0.1, which is used for modeling the solar spectrum. In addition, we have measured previously unidentified Fe X lines that will need to be added to CHIANTI and other spectroscopic databases.Graphical

High-precision Transition Energy Measurements of Neon-like Fe xvii Ions

We improve by a factor of 4–20 the energy accuracy of the strongest soft X-ray transitions of Fe xvii ions by resonantly exciting them in an electron beam ion trap with a monochromatic beam at the P04 beamline of the PETRA III synchrotron facility. By simultaneously tracking instantaneous photon-energy fluctuations with a high-resolution photoelectron spectrometer, we minimize systematic uncertainties down to 10–15 meV, or velocity equivalent ±∼5 km s−1 in their rest energies, substantially improving our knowledge of this key astrophysical ion. Our large-scale configuration-interaction computations include more than 4 million relativistic configurations and agree with the experiment at a level without precedent for a 10-electron system. Thereby, theoretical uncertainties for interelectronic correlations become far smaller than those of quantum electrodynamics (QED) corrections. The present QED benchmark strengthens our trust in future calculations of many other complex atomic ions of interest to astrophysics, plasma physics, and the development of optical clocks with highly charged ions.

High resolution X-ray spectra of the time evolution of emission from metastable electronic states of highly charged Ni-like ions

Metastable levels of highly charged ions that can only decay via highly forbidden transitions can have a significant effect on the properties of high temperature plasmas. For example, the highly forbidden 3d10\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{10}$$\\end{document}J=0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_{J=0}$$\\end{document} - 3d9\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^9$$\\end{document}4 s (52,12)J=3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$(\\frac{5}{2},\\frac{1}{2})_{J=3}$$\\end{document} magnetic octupole (M3) transition in nickel-like ions can result in a large metastable population of its upper level which can then be ionized by electrons of energies below the ground state ionization potential. We present a method to study metastable electronic states in highly charged ions that decay by x-ray emission in electron beam ion traps (EBIT). The time evolution of the emission intensity can be used to study the parameters of ionization balance dynamics and the lifetime of metastable states. The temporal and energy resolution of a new transition-edge sensor microcalorimeter array enables these studies at the National Institute of Standards and Technology EBIT.Graphical abstractNOMAD calculated time evolution of the ratio of the Ni-like and Co-like lines in Nd at varying electron densities compared with measured ratios

Extraction experiments at the UNIST electron beam ion trap for highly charged ion studies

Highly charged ions (HCIs) are currently utilized in numerous fundamental and applied sciences, including astrophysics, dark matter search, optical clocks, semiconductor lithography, and quantum dot fabrication, to name just a few examples. At Ulsan National Institute of Science and Technology (UNIST), a tabletop electron beam ion trap (EBIT) has been developed for creating and studying HCIs. The UNIST-EBIT compresses the electron beam by 72 permanent magnets (up to 0.84 T) and produces up to He-like Ar ions. The primary objective of the UNIST-EBIT is to obtain X-ray spectrum data essential in astrophysics. Meanwhile, optical clocks based on HCIs are receiving significant attention from the scientific community. The UNIST-EBIT can also provide various HCIs for optical clock applications. For this purpose, designing an extraction beamline along with an initial extraction experiment of Ar ions from the EBIT is underway. To extract Ar ions, we consider constructing an automatic control system with EPICS. In this work, we present the recent progress of the UNIST-EBIT for extraction experiments.

High-Current Capability and Upgrades of the EBIS/T Charge-Breeding System in the Reaccelerator at the Facility for Rare-Isotope Beams

The Reaccelerator (ReA) of the Facility for Rare-Isotope Beams (FRIB) at Michigan State University uses a Beam Cooler/Buncher (BCB) and an Electron-Beam Ion Trap (EBIT) as a charge-breeding injector system. The rare isotopes produced by In-flight Separation are selected by the Advanced Rare Isotope Separator (ARIS) and stopped in a helium gas cell. Long-lived and stable-isotope beams can also be extracted from a Batch-Mode Ion Source (BMIS). The continuous beams transported at low energy to ReA are injected into the BCB. The pulsed beams are then injected into the EBIT, charge bred, ejected, and accelerated by ReA’s LINAC. The EBIT electron current (300 - 600 mA) is a factor that limits its capacity to ∼2×1010 elementary charges, which restricts the maximum EBIT-extracted rates to less than 2×1010 particles per second for light ions. An upgrade of the EBIT electron gun is expected to provide 2 A in current. In parallel, a High-Current Electron-Beam Ion Source (HCEBIS) is being commissioned. The HCEBIS can presently provide an electron current of 2 A. An upgrade will increase the current to 4 A. The implementation of these two upgrades is expected to allow for maximum rates to be ∼1011 pps, compatible with FRIB projected rates and user demands. We review the high-current capabilities and upgrades of ReA’s charge-breeding system.

Status of the High-Current Electron-Beam Ion Source Charge Breeder for the Facility for Rare-Isotope Beams

The Reaccelerator (ReA) of the Facility for Rare-Isotope Beams (FRIB) employs an Electron-Beam Ion Trap (EBIT) as a charge breeder to reaccelerate rare-isotope beams up to 12 MeV/u. The ReA EBIT produces an electron current of 300 – 600 mA. The maximum trap capacity of the ReA EBIT is 1010 elementary charges. FRIB production rates are expected to exceed 1010 particles/s in some cases in the future. There is also a user demand for reaccelerated stable-isotope beams of more than 1010 pps. To handle these rates and provide redundancy, a High Current Electron-Beam Ion Source (HCEBIS) has been built and is now being commissioned. An electron-beam current of 2 A with a 50 % duty cycle has been transported through a 4-T field. An upcoming upgrade to increase the electron-beam current up to 4 A will allow for a maximum trap capacity of 2.4×1011 elementary charges. We present the status of the HCEBIS, including the results of the electron-beam commissioning and systematic studies.

The 3d 2 D 5/2−2 D 3/2 magnetic dipole transition in potassium-like ions

Spectral lines of the magnetic-dipole transition between the 3d2D3/2,5/2 levels of K-like Kr17+, Zr21+, Nb22+, Mo23+, and Ru25+ ions were measured in a compact electron beam ion trap. By means of dedicated calibration methods, the transition wavelengths of Kr17+, Zr21+, and Mo23+ ions reduce uncertainties by at least one order of magnitude and the wavelengths of Nb22+ and Ru25+ ions are measured for the first time at a few ppm level. In addition, the fine-structure energy splittings were systematically calculated using the multiconfiguration Dirac–Hartree–Fock method combined with the relativistic configuration interaction approach. The contributions of the core-valence and core-core electron correlations, the Breit interaction and QED effect were discussed in detail. The results show that it is essential to include deep core-valence correlation of L-shell and core-core valence correlation of 3p subshell to obtain an agreement better than 0.15% with existing experimental values. The calculation model can be performed to predict the wavelength within a high accuracy for a wide range of potassium-like ions.

Excitation and recombination studies with silicon and sulphur ions at an EBIT

Measurements of electron-impact excitation and recombination rate coefficients of highly charged Si and S ions at the Stockholm electron beam ion trap are reported. The experimental method was a combination of photon detection from the trapped ions during probing and subsequently extraction and time-of-flight (TOF) charge analysis of these ions. The TOF technique allows to measure recombination rate coefficients separately for every charge state, and together with the photon spectra of these ions also the excitation rate coefficients. In this paper, we present more details of the experimental procedure and summarize the experimental results in comparison with two different state-of-the-art calculations of recombination and excitation rates for Si10+–Si13+ and S12+–S15+ ions. One of these uses a relativistic configuration interaction approach (flexible atomic code) and the other is a relativistic many-body perturbation theory. A good to excellent agreement with both of them is found in energy and resonance strength for the investigated ions.

Investigation of optical spectroscopy in W13+ ions

This study presents the investigation of magnetic dipole transition lines of W13+ ions in the wavelength range of 200–700 nm at a low-energy electron beam ion trap. Seventeen lines emitted from W13+ ions have been observed with three being reported experimentally for the first time. The atomic structure calculation and spectra simulation of W13+ ions have been carried out using the multiconfiguration Dirac–Hartree–Fock method combined with the relativistic configuration interaction approach and the collisional–radiative model, respectively. The theoretical calculations are in reasonable agreement with the experimental observations, and most of the observed lines have been identified.

Charge exchange of slow highly charged ions from an electron beam ion trap with surfaces and 2D materials

Abstract Electron beam ion traps allow studies of slow highly charged ion transmission through freestanding 2D materials as an universal testbed for surface science under extreme conditions. Here we review recent studies on charge exchange of highly charged ions in 2D materials. Since the interaction time with these atomically thin materials is limited to only a few femtoseconds, an indirect timing information will be gained. We will therefore discuss the interaction separated in three participating time regimes: energy deposition (charge exchange), energy release (secondary particle emission), and energy retention (material modification).

L-Mn dielectronic recombination of cerium ions in a room-temperature EBIT

We explore the dielectronic recombination structures at the electron beam ion trap at Jagiellonian University in Cracow, emited by cerium that is produced by the high-current cathode made of iridium and cerium. Small amounts of these elements evaporate from the cathode and form low-intensity admixtures within the electron-ion plasma in the EBIT. Their presence and specific ionic population can be observed by examining the spectral characteristics resulting from the DR process. Results have been compared with flexible atomic code calculations, working in unresolved transition array mode, providing identification of the charge states. Here we show that this mode provides quick calculations of very complex data with enough reliability for experimental comparison. These observations highlight which DR features and corresponding charge states that should be present in spectra obtained in EBITs with similar cathode specifications.

Electron collisional excitation cross-section measurements and modeling for select Ni-like to Ge-like gold transitions

We have experimentally determined the electron collisional excitation cross-sections for several 3d→4f and 3d→5f excitations in Ni- to Ge-like Au at energies of ∼ 0.4, 1, 2, and 3 keV above threshold energy, ET, for the 3d→4f excitations ( ET ∼ 2.5 keV) and ∼ 0.2, 1, and 2 keV above threshold energy for the 3d→5f excitations ( ET ∼ 3.3 keV). The cross-section measurements are possible by using the GSFC micro-calorimeter to record emission spectra from beam plasmas created in the Livermore EBIT-I electron beam ion trap. The cross-sections are experimentally determined from the ratio of the measured intensities of the collisionally excited lines to the intensities of the radiative recombination lines in monoenergetic electron distribution EBIT-I plasmas. The effects of polarization and Auger processes in the beam plasmas are accounted for in the cross-section determination. Experimentally determined cross-sections are compared with those from HULLAC, DWS, and FAC calculations. The measurements exhibit significant differences with the calculations of these excitation cross-sections.

Development and commissioning of the UNIST electron beam ion trap

Development and commissioning of the UNIST electron beam ion trap

Precision measurement of M1 optical clock transition in Ni12+

Highly charged ions (HCIs) have drawn significant interest in quantum metrology and in the search for new physics. Among these, Ni12+ is considered as one of the most promising candidates for the next generation of HCI optical clocks, due to its two E1-forbidden transitions M1 and E2, which occur in the visible spectral range. In this work, we used the Shanghai-Wuhan electron beam ion trap to perform a high-precision measurement of the M1 transition wavelength. Our approach involved an improved calibration scheme for the spectra, utilizing auxiliary Ar+ lines for calibration and correction. Our final measured result of the M1 transition wavelength demonstrates a fivefold improvement in accuracy compared to our previous findings, reaching the subpicometer level accuracy. In combination with our rigorous atomic-structure calculations to capture the electron correlations and relativistic effects, the quantum electrodynamic corrections were extracted. Published by the American Physical Society 2024

Experimental and theoretical research progress of <sup>2</sup>P<sub>1/2 </sub> – <sup>2</sup>P<sub>3/2</sub> transitions of highly charged boron-like ions

The precise measurement of the fine structure and radiative transition properties of highly charged ions (HCI) is essential for testing fundamental physical models, including strong-field quantum electrodynamics (QED) effects, electron correlation effects, relativistic effects, and nuclear effects. These measurements also provide critical atomic physics parameters for astrophysics and fusion plasma physics. Compared with the extensively studied hydrogen-like and lithium-like ion systems, boron-like ions exhibit significant contributions in terms of relativistic and QED effects in their fine structure forbidden transitions. High-precision experimental measurements and theoretical calculations of these systems provide important avenues for further testing fundamental physical models in multi-electron systems. Additionally, boron-like ions are considered promising candidates for HCI optical clocks. This paper presents the latest advancements in experimental and theoretical research on the ground state <sup>2</sup>P<sub>3/2</sub>—<sup>2</sup>P<sub>1/2</sub> transition in boron-like ions, and summarizes the current understanding of their fine and hyperfine structures. It also discusses a proposed experimental setup for measuring the hyperfine splitting of boron-like ions by using an electron beam ion trap combined with high-resolution spectroscopy. This proposal aims to provide a reference for future experimental research on the hyperfine splitting of boron-like ions, to test the QED effects with higher precision, extract the radius of nuclear magnetization distribution, and validate relevant nuclear structure models.