Atoms

13 pages, 6452 KiB

Open AccessArticle

Evaluation of Spatial Profile of Local Emissions from W¹⁷⁺–W²³⁺ Unresolved Transition Array Spectra

by Ryota Nishimura, Tetsutarou Oishi, Izumi Murakami, Daiji Kato, Hiroyuki A. Sakaue, Hayato Ohashi, Shivam Gupta, Chihiro Suzuki, Motoshi Goto, Yasuko Kawamoto, Tomoko Kawate, Hiroyuki Takahashi and Kenji Tobita

Atoms 2025, 13(2), 21; https://doi.org/10.3390/atoms13020021 - 18 Feb 2025

Viewed by 493

Abstract

Tungsten (W) spectroscopy has attracted significant attention because W is one of the major impurities in ITER and future DEMO reactors. W²²⁺–W³³⁺ spectra at 15–45 Å have been useful for impurity diagnostics. Unresolved Transition Array (UTA) spectra around 200 Å, [...] Read more.

Tungsten (W) spectroscopy has attracted significant attention because W is one of the major impurities in ITER and future DEMO reactors. W²²⁺–W³³⁺ spectra at 15–45 Å have been useful for impurity diagnostics. Unresolved Transition Array (UTA) spectra around 200 Å, which contain W¹⁷⁺–W²³⁺, have potential for diagnostics tungsten ions in even lower charge states. Because multiple charge states overlap with very similar wavelengths, it is challenging to evaluate impurity spatial profiles from UTA spectra around 200 Å. In this study, we conducted tungsten pellet injection experiments in Large Helical Device (LHD) and attempted to evaluate the spatial profiles of UTA spectra around 200 Å, observed at 0.3–0.8 keV of central electron temperature. The results indicated that tungsten ions around W²⁰⁺ were locally profiled in a radial region, r_eff = 0.38 m, where the local electron temperature decreases by 30% to 40% with respect to more central and outer temperatures. These results suggested that the UTA spectrum around 200 Å would be useful for diagnostics of tungsten impurities in lower charge states than the charge states contained in UTA spectra around 15–45 Å. Full article

(This article belongs to the Section Atomic, Molecular and Nuclear Spectroscopy and Collisions)

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10 pages, 4991 KiB

Open AccessArticle

Interaction Between Atoms and Structured Light Fields

by Shreyas Ramakrishna and Stephan Fritzsche

Atoms 2025, 13(2), 20; https://doi.org/10.3390/atoms13020020 - 13 Feb 2025

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Abstract

Structured light encompasses a vast variety of light fields. It has unique properties such as non-uniform transverse intensity and a polarization pattern across their beam cross-sections. In this contribution, we discuss the photoexcitation of a single ionic target system driven by different sets [...] Read more.

Structured light encompasses a vast variety of light fields. It has unique properties such as non-uniform transverse intensity and a polarization pattern across their beam cross-sections. In this contribution, we discuss the photoexcitation of a single ionic target system driven by different sets of structured light modes. Specifically, we provide a compilation of transition amplitudes for various structured light modes interacting with atomic systems based on the first-order perturbation theory. To illustrate this, we will choose an electric quadrupole transition (

4 s {}^{2}{S_{1 / 2}} \to 3 d {}^{2}{D_{5 / 2}}

) in the target Ca⁺ ion driven by a structured light field. For this particular interaction, we examine how the beam parameters affect the population of magnetic sub-levels in the atomic excited state. Full article

(This article belongs to the Special Issue 21st International Conference on the Physics of Highly Charged Ions)

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5 pages, 363 KiB

Open AccessCommunication

Bound–Free and Free–Free Pair Production Channels in Forward Delbrück Scattering

by Jonas Sommerfeldt, Vladimir A. Yerokhin and Andrey Surzhykov

Atoms 2025, 13(2), 19; https://doi.org/10.3390/atoms13020019 - 12 Feb 2025

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Abstract

We present a theoretical study of forward-angle Delbrück scattering of light by the Coulomb field of a target nucleus. Special attention is paid to the Coulomb corrections, which take into account the interaction of the emerging virtual electron–positron pairs with the nucleus to [...] Read more.

We present a theoretical study of forward-angle Delbrück scattering of light by the Coulomb field of a target nucleus. Special attention is paid to the Coulomb corrections, which take into account the interaction of the emerging virtual electron–positron pairs with the nucleus to higher orders of

α Z

. We compare the results from three different computation methods: the direct all-order evaluation of the Delbrück amplitude, the computation from the pair production cross section with the optical theorem and the low-energy limit. We find that the values obtained from the optical theorem are in very good agreement with the all-order calculations and can be used as benchmark data. Moreover, both methods agree with the low-energy limit for photon energies

ω < < m_{e} c^{2}

when correctly accounting for the bound–free pair production cross section in the optical theorem calculations, and the discrepancy found in the literature originates from neglecting this contribution. Full article

(This article belongs to the Special Issue 21st International Conference on the Physics of Highly Charged Ions)

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14 pages, 749 KiB

Open AccessArticle

Modelling of X-Ray Spectra Originating from the He- and Li-like Ni Ions for Plasma Electron Temperature Diagnostics Purposes

by Karol Kozioł, Andrzej Brosławski and Jacek Rzadkiewicz

Atoms 2025, 13(2), 18; https://doi.org/10.3390/atoms13020018 - 9 Feb 2025

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Abstract

The multi-configurational Dirac–Hartree–Fock method has been used to examine the electron correlation effect on wavelengths and transition rates for

L \to K

transitions occurring in He- and Li-like nickel ions. The collisional-radiative modelling approach has been used to simulate the X-ray spectra, in [...] Read more.

The multi-configurational Dirac–Hartree–Fock method has been used to examine the electron correlation effect on wavelengths and transition rates for

L \to K

transitions occurring in He- and Li-like nickel ions. The collisional-radiative modelling approach has been used to simulate the X-ray spectra, in a 1.585–1.620 Å wavelength range, originating from the He-like nickel ions and their dielectronic Li-, Be-, and B-like satellites for various electron temperature values in the 2 keV to 8 keV range. The presented results may be useful in improving the plasma electron temperature diagnostics based on nickel spectra. Full article

(This article belongs to the Special Issue Atom and Plasma Spectroscopy)

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9 pages, 900 KiB

Open AccessArticle

Visible Light Spectroscopy of W¹⁴⁺ Ions in an Electron Beam Ion Trap

by Ben Niu, Zhaoying Chen, Jihui Chen, Yanting Li, Fangshi Jia, Bingli Li, Zhencen He, Jun Xiao, Yaming Zou and Ke Yao

Atoms 2025, 13(2), 17; https://doi.org/10.3390/atoms13020017 - 8 Feb 2025

Viewed by 572

Abstract

In this work, the visible lines of

W^{14 +}

ions in the wavelength range of 400–650 nm are investigated experimentally and theoretically. The experiments were performed in a low-energy electron beam ion trap. The simulated spectra of

W^{14 +}

ions (Nd-like) [...] Read more.

In this work, the visible lines of

W^{14 +}

ions in the wavelength range of 400–650 nm are investigated experimentally and theoretically. The experiments were performed in a low-energy electron beam ion trap. The simulated spectra of

W^{14 +}

ions (Nd-like) were obtained from atomic structure computations in combination with a collisional–radiative model. Overall, there is a reasonable similarity between the measurements and the results of the simulations, and most of the twelve observed spectral lines associated with

W^{14 +}

were tentatively identified. Full article

(This article belongs to the Special Issue 21st International Conference on the Physics of Highly Charged Ions)

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13 pages, 807 KiB

Open AccessArticle

High-Resolution Fourier Transform Spectra of Atomic Sulfur: Testing of Modified Quantum Defect Theory

by Vladislav E. Chernov, Nikolai L. Manakov, Alexei V. Meremianin, Alexander V. Naskidashvili, Svatopluk Civiš, Martin Ferus, Petr Kubelík, Ekaterina M. Zanozina and Oxana V. Zetkina

Atoms 2025, 13(2), 16; https://doi.org/10.3390/atoms13020016 - 8 Feb 2025

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Abstract

QDT (quantum defect theory) is an effective technique for calculating processes involving highly excited (Rydberg) states of atoms, ions, and molecules with one valence electron outside filled shells, whose spectrum generally resembles a hydrogen-like atom’s spectrum. At the expense of some modification of [...] Read more.

QDT (quantum defect theory) is an effective technique for calculating processes involving highly excited (Rydberg) states of atoms, ions, and molecules with one valence electron outside filled shells, whose spectrum generally resembles a hydrogen-like atom’s spectrum. At the expense of some modification of QDT, in this paper, we extend its applicability to describe low- and intermediate-excited levels of atoms with more complex spectra (on the example of atomic sulfur S I). Transitions between just such states are responsible for the infrared (IR) spectra of atoms. While the quantum defects (QDs) of the highly excited Rydberg levels are determined by the energies of individual levels near the ionization threshold, the radial wave functions of low excited electronic states, in the framework of our modification of QDT, include the QD dependence on energy over a wide energy range; this dependence is determined from the whole spectral series. We show that, outside the atomic core domain, the electron radial functions calculated using modified semi-phenomenological QDT agree well with ab initio calculations. As another assessment of QDT accuracy, we show satisfactory agreement of the probabilities of dipole transitions in S I, taken from the NIST Atomic Spectra Database, with our QDT calculations. We perform an indirect experimental verification of QDT on the basis of spectra of S I in gas-discharge plasma measured by time-resolved high-resolution Fourier transfer spectroscopy (FTS). The Boltzmann plot built from our measured spectra demonstrates that QDT provides a satisfactory approximation for calculating the experimental lines’ intensities. Full article

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8 pages, 490 KiB

Open AccessArticle

Diagnostics of Spin-Polarized Ions at Storage Rings

by Anna Maiorova, Stephan Fritzsche, Andrey Surzhykov and Thomas Stöhlker

Atoms 2025, 13(2), 15; https://doi.org/10.3390/atoms13020015 - 4 Feb 2025

Viewed by 558

Abstract

Polarized heavy ions in storage rings are seen as a valuable tool for a wide range of research, from the study of spin effects in relativistic atomic collisions to the tests of the Standard Model. For forthcoming experiments, several important challenges need to [...] Read more.

Polarized heavy ions in storage rings are seen as a valuable tool for a wide range of research, from the study of spin effects in relativistic atomic collisions to the tests of the Standard Model. For forthcoming experiments, several important challenges need to be addressed to work efficiently with such ions. Apart from the production and preservation of ion polarization in storage rings, its measurement is an extremely important issue. In this contribution, we employ the radiative recombination (RR) of polarized electrons into the ground state of initially hydrogen-like, finally helium-like, ions as a probe process for beam diagnostics. Our theoretical study clearly demonstrates that the RR cross section, integrated over photon emission angles, is highly sensitive to both the degree and the direction of ion polarization. Since the (integrated) cross-section measurements are well established, the proposed method offers promising prospects for ion spin tomography at storage rings. Full article

(This article belongs to the Special Issue 21st International Conference on the Physics of Highly Charged Ions)

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9 pages, 521 KiB

Open AccessArticle

Experimental Cross Sections for Electron-Impact Single, Double, and Triple Ionization of La⁺

by B. Michel Döhring, Alexander Borovik, Jr., Florian Gocht, Kurt Huber and Stefan Schippers

Atoms 2025, 13(2), 14; https://doi.org/10.3390/atoms13020014 - 28 Jan 2025

Viewed by 748

Abstract

We report on new measurements of absolute cross sections for single, double, and triple electron-impact ionization of singly charged lanthanum ions. The resulting single and double ionization cross sections are in fair agreement with results from previous experimental work. In the present work, [...] Read more.

We report on new measurements of absolute cross sections for single, double, and triple electron-impact ionization of singly charged lanthanum ions. The resulting single and double ionization cross sections are in fair agreement with results from previous experimental work. In the present work, we extended the experimental range by a factor of two to approx. 2000 eV. To the best of our knowledge, there have been no previous measurements of triple ionization. The present work in progress aims to provide vitally needed atomic data for the astrophysical modeling of kilonovae. Full article

(This article belongs to the Special Issue 21st International Conference on the Physics of Highly Charged Ions)

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12 pages, 4934 KiB

Open AccessArticle

In Situ Study of the Temperature and Fluence Dependence of Yb²⁺ Luminescence in Yttrium Aluminum Garnet (YAG) Single Crystals

by Ruotong Chang, Yingjie Song, Hongtao Hu, Shasha Lv, Guangfu Wang and Menglin Qiu

Atoms 2025, 13(2), 13; https://doi.org/10.3390/atoms13020013 - 27 Jan 2025

Viewed by 656

Abstract

In this study, ion-beam-induced luminescence with 2 MeV H⁺ was used to excite YAG single crystals at different temperatures. Under several constant temperatures, the luminescence intensity of Yb²⁺ monotonically decreases with increasing fluence, eventually reaching approximately 35% of the initial intensity [...] Read more.

In this study, ion-beam-induced luminescence with 2 MeV H⁺ was used to excite YAG single crystals at different temperatures. Under several constant temperatures, the luminescence intensity of Yb²⁺ monotonically decreases with increasing fluence, eventually reaching approximately 35% of the initial intensity at a fluence of 3.5 × 10¹⁴ cm⁻². The nonmonotonic evolution behavior of Yb²⁺ luminescence intensity with temperature can be effectively described by the intermediate-state model under consecutive temperature variations. The presence of an intermediate state may be the primary cause of the negative thermal quenching of Yb²⁺ luminescence. Yb²⁺ luminescence intensity decreased to 60% of the initial intensity when the temperature was continuously varied in the 100–300 K range, although the peak position remained rather stable. The luminescence of Yb²⁺ exhibits good radiation resistance and thermal stability in the experimental temperature range. Full article

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9 pages, 799 KiB

Open AccessArticle

Single and Double Electron Capture by 1–16 keV Sn⁴⁺ Ions Colliding on H₂

by Emiel de Wit, Lennart Tinge, Klaas Bijlsma and Ronnie Hoekstra

Atoms 2025, 13(2), 12; https://doi.org/10.3390/atoms13020012 - 24 Jan 2025

Viewed by 618

Abstract

Single and double electron capture cross-sections for collisions of ¹¹⁸Sn⁴⁺ with molecular hydrogen have been measured in an energy range of 1 keV to 16 keV using a crossed-beam setup. The cross-sections are determined from measurements of charge-state-resolved ion currents obtained [...] Read more.

Single and double electron capture cross-sections for collisions of ¹¹⁸Sn⁴⁺ with molecular hydrogen have been measured in an energy range of 1 keV to 16 keV using a crossed-beam setup. The cross-sections are determined from measurements of charge-state-resolved ion currents obtained through a retarding field analyser. Remarkably, the single electron capture cross-sections for Sn⁴⁺ are more than a factor 3 smaller than the previously determined single electron capture cross-sections for Sn³+–H₂ collisions and the double electron capture cross-sections are only about 20% smaller than the single electron capture cross-sections. These results are understood on the basis of potential energy curve crossings. The first active curve crossings for the Sn⁴⁺–H₂ system happen at a relatively small internuclear distance of about 5.5 a.u., which should be compared to 8 a.u. for Sn³+ ions. Multi-channel Landau–Zener calculations have been performed for single electron capture and confirm these low cross-sections. The curve crossing for double electron capture by Sn⁴⁺ lies very close to the one for single electron capture, which may explain the single and double electron capture cross-sections being of similar magnitude. Full article

(This article belongs to the Special Issue 21st International Conference on the Physics of Highly Charged Ions)

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11 pages, 1763 KiB

Open AccessArticle

Density Functional Theory Study of Hydrogen Adsorption on Al-U Alloy Surfaces

by Xiaoting Wang, Min Guan, Duo You, Dong Xie, Mingxi Hou and Yongxiang Leng

Atoms 2025, 13(2), 9; https://doi.org/10.3390/atoms13020009 - 21 Jan 2025

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Abstract

To better understand the hydrogen corrosion mechanism on uranium surfaces and assess the hydrogen penetration resistance of Al-U alloys, the adsorption of hydrogen atoms on U(110), Al(111), and nAl/U(110) alloy surfaces was systematically studied through density functional theory (DFT) calculations. The results reveal [...] Read more.

To better understand the hydrogen corrosion mechanism on uranium surfaces and assess the hydrogen penetration resistance of Al-U alloys, the adsorption of hydrogen atoms on U(110), Al(111), and nAl/U(110) alloy surfaces was systematically studied through density functional theory (DFT) calculations. The results reveal that when U is alloyed with Al, the adsorption behavior of H atom on its surface thereon changes greatly. Specifically, the adsorption energy of H decreases with increasing Al content, indicating a weakening of the interaction between the H atom and the surface. A correlation between binding strength and alloy composition was established using d-band center theory. The incorporation of Al atoms alters the electronic structure of the U(110) surface, shifting the d-band center of uranium atoms downward. This shift results in a weakened interaction between the adsorbed H atom and the alloy surface. Full article

(This article belongs to the Section Quantum Chemistry, Computational Chemistry and Molecular Physics)

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18 pages, 1928 KiB

Open AccessArticle

Calculated Transition Probabilities for Os VI Spectral Lines of Interest to Nuclear Fusion Research

by Maxime Brasseur, Patrick Palmeri and Pascal Quinet

Atoms 2025, 13(2), 11; https://doi.org/10.3390/atoms13020011 - 21 Jan 2025

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Abstract

In this work, we present a new set of transition probabilities for experimentally classified spectral lines in the Os VI spectrum. To do this, two independent computational approaches based on the pseudo-relativistic Hartree–Fock, including core polarization effects (HFR+CPOL) and fully relativistic Multiconfiguration Dirac–Hartree–Fock [...] Read more.

In this work, we present a new set of transition probabilities for experimentally classified spectral lines in the Os VI spectrum. To do this, two independent computational approaches based on the pseudo-relativistic Hartree–Fock, including core polarization effects (HFR+CPOL) and fully relativistic Multiconfiguration Dirac–Hartree–Fock (MCDHF) methods, were used, with the detailed comparison of the results obtained with these two approaches allowing us to estimate the quality of the calculated radiative parameters. These atomic data, corresponding to 367 lines of five-times ionized osmium between 438.720 and 1486.275 Å, are expected to be useful for the analysis of the spectra emitted by fusion plasmas in which osmium could appear as a result of transmutation by the neutron bombardment of tungsten used as component of the reactor wall, such as the ITER divertor. Full article

(This article belongs to the Special Issue Atom and Plasma Spectroscopy)

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6 pages, 259 KiB

Open AccessCommunication

Lithium-like O⁵⁺ Emission near 19 Å

by Jaan K. Lepson, Gregory V. Brown, Joel H. T. Clementson, Alexander J. Fairchild, Ming Feng Gu, Natalie Hell, Elmar Träbert and Peter Beiersdorfer

Atoms 2025, 13(2), 10; https://doi.org/10.3390/atoms13020010 - 21 Jan 2025

Viewed by 551

Abstract

Using a high-resolution grating spectrometer on the Livermore EBIT-I electron beam ion trap, we have measured three

n = 3, 4 \to n = 1

K-shell emission lines in lithium-like O

5^{+}

, which are situated near the O VIII Lyman- [...] Read more.

Using a high-resolution grating spectrometer on the Livermore EBIT-I electron beam ion trap, we have measured three

n = 3, 4 \to n = 1

K-shell emission lines in lithium-like O

5^{+}

, which are situated near the O VIII Lyman-

α

lines at 19 Å. Two of the resulting wavelengths agree well with the wavelengths of these lines we reported earlier, but the wavelength of the third line does not. In contrast, our new wavelengths now fully agree with those from resonant photo-absorption experiments on the PETRA III synchrotron facility. Full article

(This article belongs to the Special Issue 21st International Conference on the Physics of Highly Charged Ions)

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Atoms, Volume 13, Issue 2 (February 2025) – 13 articles

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