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Atomic and Molecular Spectra in Magnetically Confined Torus Plasmas

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A special issue of Atoms (ISSN 2218-2004).

Deadline for manuscript submissions: closed (15 September 2021) | Viewed by 16998

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Special Issue Editors

Dr. Chihiro Suzuki

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Guest Editor

National Institute for Fusion Science, 322-6 Oroshi-cho, Toki 509-5292, Japan
Interests: highly charged ions; spectroscopy; heavy ions; helical devices; atomic database; collisional radiative modeling

Dr. Izumi Murakami

E-Mail Website
Guest Editor

National Institute for Fusion Science, Toki 509-5292, Japan
Interests: collisional-radiative model for fusion and astronomical plasmas; atomic structure; atomic database

Special Issue Information

Dear Colleagues,

A variety of atomic and molecular processes occur in magnetically confined torus plasmas for fusion research, such as tokamaks and helical devices, because of their unique plasma characteristics. Even though spectroscopic studies on hydrogen (and its isotopes) atoms and molecules are well developed, it is still a hot topic, relevant to the presence of fast particles, complex fundamental processes, and strong magnetic fields. Intrinsic/extrinsic impurities with various atomic numbers exist in fusion plasmas. Intrinsic impurities arising from plasma–wall interactions include beryllium, carbon, iron, molybdenum, and heavier elements. Emission spectra of heavy ions have recently attracted considerable attention since tungsten has been adopted as a divertor material in the ITER tokamak. A variety of extrinsic impurities are often injected into fusion plasmas with pellet or gas puffing for the purpose of impurity transport study or divertor heat load mitigation. In addition, fusion plasmas can be exploited for spectroscopic studies relevant not only to fusion but also to astrophysics, plasma applications, and basic atomic physics, thanks to the availability of state-of-the-art diagnostic tools.

The scope of this Special Issue is recent experimental and theoretical advances in relation to atomic and molecular spectra in magnetically confined torus plasmas. As mentioned above, the capability of fusion plasmas allows us to investigate a number of elements, from hydrogen to heavy elements, which entirely covers the periodic table. As the electron temperature ranges from a few eV (edge) to 10 keV (core) in fusion plasmas, a wide range of charge states, from neutral to hydrogen-like ions, must be investigated. These investigations are associated with different spectroscopic techniques optimized for specific photon energies. Furthermore, prediction/validation of experimental spectra using collisional radiative modeling and other basic experiments such as EBITs is also of great interest. Spectral line shapes including shifts, widths and splittings are important as powerful diagnostic tools in fusion plasmas. Review papers relevant to the above topics are also in the scope of this Special Issue.

Dr. Chihiro Suzuki
Dr. Izumi Murakami
Guest Editors

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Keywords

magnetically confined fusion
tokamaks
helical devices
plasmas
highly charged ions
spectroscopy
heavy ions
neutral atoms and molecules
spectral line shapes
atomic and molecular processes
atomic database
collisional radiative modeling

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Published Papers (6 papers)

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Research

14 pages, 6252 KiB

Open AccessArticle

Simultaneous Observation of Tungsten Spectra of W⁰ to W⁴⁶⁺ Ions in Visible, VUV and EUV Wavelength Ranges in the Large Helical Device

by Tetsutarou Oishi, Shigeru Morita, Daiji Kato, Izumi Murakami, Hiroyuki A. Sakaue, Yasuko Kawamoto, Tomoko Kawate and Motoshi Goto

Atoms 2021, 9(3), 69; https://doi.org/10.3390/atoms9030069 - 17 Sep 2021

Cited by 8 | Viewed by 2662

Abstract

Spectroscopic studies for emissions released from tungsten ions have been conducted in the Large Helical Device (LHD) for contribution to the tungsten transport study in tungsten divertor fusion devices and for expansion of the experimental database of tungsten line emissions. Tungsten ions are distributed in the LHD plasma by injecting a pellet consisting of a small piece of tungsten metal wire enclosed by a carbon tube. Line emissions from W⁰, W⁵⁺, W⁶⁺, W²⁴⁺–W²⁸⁺, W³⁷⁺, W³⁸⁺, and W⁴¹⁺–W⁴⁶⁺ are observed simultaneously in the visible (3200–3550 Å), vacuum ultraviolet (250–1050 Å), and extreme ultraviolet (5–300 Å) wavelength ranges and the wavelengths are summarized. Temporal evolutions of line emissions from these charge states are compared for comprehensive understanding of tungsten impurity behavior in a single discharge. The charge distribution of tungsten ions strongly depends on the electron temperature. Measurements of emissions from W¹⁰⁺ to W²⁰⁺ are still insufficient, which is addressed as a future task. Full article

(This article belongs to the Special Issue Atomic and Molecular Spectra in Magnetically Confined Torus Plasmas)

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10 pages, 2047 KiB

Open AccessArticle

Emission Lines in 290–360 nm of Highly Charged Tungsten Ions W²⁰⁺–W²⁹⁺

by Shota Era, Daiji Kato, Hiroyuki A. Sakaue, Toshiki Umezaki, Nobuyuki Nakamura and Izumi Murakami

Atoms 2021, 9(3), 63; https://doi.org/10.3390/atoms9030063 - 8 Sep 2021

Cited by 3 | Viewed by 2547

Abstract

Forbidden transitions in the near-UV and visible wavelength of highly charged tungsten (W) ions are potentially useful as novel tungsten diagnostics means of fusion plasmas. Emission lines in 290–360 nm from W

^{q +}

ions interacting with an electron beam of 540–1370 eV [...] Read more.

^{q +}

ions interacting with an electron beam of 540–1370 eV are measured, using a compact electron-beam-ion-trap. The charge states of 64 lines are identified as W

^{20 +}

–W

^{29 +}

. A magnetic-dipole (M1) line of W

^{29 +}

between the excited states

(4 d^{8} 4 f) {[{(4 d_{5 / 2}^{- 2})}_{4} 4 f_{7 / 2}]}_{13 / 2} \to {[{(4 d_{5 / 2}^{- 2})}_{4} 4 f_{5 / 2}]}_{13 / 2}

is newly identified; the wavelength is determined as 351.03(10) nm in air. The theoretical wavelength calculated using the multiconfiguration Dirac–Hartree–Fock method is in a good agreement with the measurement. Full article

(This article belongs to the Special Issue Atomic and Molecular Spectra in Magnetically Confined Torus Plasmas)

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18 pages, 2110 KiB

Open AccessArticle

Evaluation of Fe XIV Intensity Ratio for Electron Density Diagnostics by Laboratory Measurements

by Nagaaki Kambara, Tomoko Kawate, Tetsutarou Oishi, Yasuko Kawamoto, Hiroyuki A. Sakaue, Daiji Kato, Nobuyuki Nakamura, Hirohisa Hara and Izumi Murakami

Atoms 2021, 9(3), 60; https://doi.org/10.3390/atoms9030060 - 30 Aug 2021

Cited by 1 | Viewed by 3012

Abstract

The intensity ratio of Fe XIV 264.765A/274.203A is useful to determine the electron density of solar corona, and the relationship between the electron density and the intensity ratio obtained from a model should be evaluated using laboratory plasmas to estimate the electron density more precisely. We constructed a new collisional–radiative model (CR-model) for Fe XIV (an Al-like iron ion) by considering the processes of proton-impact excitation and electron-impact ionization to the excited states of a Mg-like iron ion. The atomic data used in the CR-model were calculated using the HULLAC atomic code. The model was evaluated based on laboratory experiments using a compact electron beam ion trap, called CoBIT, and the Large Helical Device (LHD). The measured Fe XIV 264.785 Å/274.203 Å line intensity ratio with CoBIT was 1.869 ± 0.036, and it agreed well with our CR-model results. Concurrently, the measured ratio using LHD was larger than the results of our CR-model and CHIANTI. The estimated electron densities using our CR-model agreed with those from CHIANTI within a factor of 1.6–2.4 in the range of

n_{e} \approx 10^{10 - 11} {cm}^{- 3}

. Further model development is needed to explain the ratio in a high-electron density region. Full article

(This article belongs to the Special Issue Atomic and Molecular Spectra in Magnetically Confined Torus Plasmas)

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8 pages, 303 KiB

Open AccessArticle

Spectra of Ga-Like to Cu-Like Praseodymium and Neodymium Ions Observed in the Large Helical Device

by Chihiro Suzuki, Fumihiro Koike, Izumi Murakami, Tetsutarou Oishi and Naoki Tamura

Atoms 2021, 9(3), 46; https://doi.org/10.3390/atoms9030046 - 14 Jul 2021

Cited by 4 | Viewed by 2342

Abstract

Extreme ultraviolet (EUV) spectra of highly charged praseodymium (Pr) and neodymium (Nd) ions have been investigated in optically thin high-temperature plasmas produced in the Large Helical Device (LHD), a magnetically confined torus device for fusion research. Discrete spectral lines emitted mainly from highly charged ions having 4s or 4p outermost electrons were observed in plasmas with electron temperatures of 0.8–1.8 keV. Most of the isolated lines of Ga-like to Cu-like Nd ions were identified by a comparison with the recent data recorded in an electron beam ion trap (EBIT). The isolated lines of Pr ions corresponding to the identified lines of Nd ions were easily assigned from a similarity of the spectral feature for these two elements. As a result, some of the lines of Pr ions have been newly identified experimentally for the first time in this study. Full article

(This article belongs to the Special Issue Atomic and Molecular Spectra in Magnetically Confined Torus Plasmas)

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15 pages, 3732 KiB

Open AccessArticle

Plasma Spectroscopy on an Aluminum-Pellet Ablation Cloud in an LHD Plasma with an Echelle Spectrometer

by Hirotaka Tanaka, Keisuke Fujii, Taiichi Shikama, Shigeru Morita, Motoshi Goto and Masahiro Hasuo

Atoms 2020, 8(4), 81; https://doi.org/10.3390/atoms8040081 - 13 Nov 2020

Cited by 3 | Viewed by 2636

Abstract

We developed an echelle spectrometer for the simultaneous observation of the whole visible range with a high instrumental resolution, for example, 0.055 nm (full width at the half maximum) at 400 nm and 0.10 nm at 750 nm. With the spectrometer, the emission from an ablation cloud of an aluminum pellet injected into a high-temperature plasma generated in the Large Helical Device (LHD) was measured. We separated the emission lines into Al I, II, III and IV groups, and estimated the electron temperature and density of the ablation cloud from the line intensity distribution and Stark broadening respectively, of each of the Al I, II and III groups. We also determined the Stark broadening coefficients of many Al II and III lines from the respective Stark widths with the estimated electron temperature and density. Full article

(This article belongs to the Special Issue Atomic and Molecular Spectra in Magnetically Confined Torus Plasmas)

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8 pages, 2754 KiB

Open AccessArticle

Spectroscopic Measurement of Hydrogen Atom Density in a Plasma Produced with 28 GHz ECH in QUEST

by Satoru Mori, Taiichi Shikama, Kazuaki Hanada, Nao Yoneda, Arseniy Kuzmin, Masahiro Hasuo, Hiroshi Idei, Takumi Onchi, Akira Ejiri, Yuki Osawa, Yi Peng, Kyohei Matsuzaki, Shinichiro Kado, Keiji Sawada, Takeshi Ido, Kazuo Nakamura, Ryuya Ikezoe, Yoshihiko Nagashima, Makoto Hasegawa, Kengo Kuroda, Aki Higashijima, Takahiro Nagata and Shun Shimabukuro Show full author list Hide full author list

Atoms 2020, 8(3), 44; https://doi.org/10.3390/atoms8030044 - 18 Aug 2020

Cited by 3 | Viewed by 2569

Abstract

The spatial distribution of the hydrogen atom density was evaluated in a spherical tokamak (ST) plasma sustained only with 28 GHz electron cyclotron heating (ECH). The radially resolved H_δ emissivity was measured using multiple viewing chord spectroscopy and Abel inversion. A collisional-radiative (CR) model analysis of the emissivity resulted in a ground-state hydrogen atom density of 10¹⁵–10¹⁶ m⁻³ and an ionization degree of 1–0.85 in the plasma. Full article

(This article belongs to the Special Issue Atomic and Molecular Spectra in Magnetically Confined Torus Plasmas)

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