Ar XV Research Articles

Laboratory Transition-rate Measurement of the Coronal Intercombination Line of Ar xv by Time-resolved Laser Spectroscopy

The extreme-ultraviolet emission line (424 Å) of the intercombination 1s 22s 2 1 S 0–1s 22s2p 3 P 1 transition of Ar xv can potentially characterize the electron temperature of astrophysical plasma. Various theoretical studies have investigated the intercombination transition rate, which is essential for the plasma diagnostics; however, experimental difficulties have prevented its measurement. We present here measurement of the lifetime of the 3 P 1 excited state of Ar xv, providing the experimental value of the intercombination transition rate. Employing time-resolved plasma-assisted laser spectroscopy, a method we recently demonstrated, enables us to measure this submicrosecond lifetime. The experimental result exhibits a 25%–43% higher transition rate than theoretical predictions.

Theoretical study of electron-impact broadening for highly charged Ar XV ion lines

Spectral line widths produced by collisions between charged particles and emitters are of special interest for precise plasma spectroscopy. The highly charged Ar XV ion is demonstrated to have strong intrashell electron interactions, which manifest as an atomic system with many resonance structures, due to the quasi-degeneracy of orbital energies. In this paper we use the relativistic R-matrix method to investigate the electron-impact broadening of highly charged Ar XV ion spectral lines under the impact approximation. It is found that the results considering resonance structures are significantly different from those of the distorted wave approach. Furthermore, we propose a new empirical formula with a correction term to take into account the effect of resonances for electron-impact widths over a relatively wide range of plasma conditions. The corresponding fitting parameters of the new empirical formula for all 47 calculated transitions are also given with an estimated accuracy within 1%, which should be convenient for practical applications. The dataset that supported the findings of this study is available in Science Data Bank, with the link https://doi.org/10.57760/sciencedb.j00113.00101.

THE MYSTERIOUS CASE OF THE SOLAR ARGON ABUNDANCE NEAR SUNSPOTS IN FLARES

ABSTRACT Recently we discussed an enhancement of the abundance of Ar xiv relative to Ca xiv near a sunspot during a flare, observed in spectra recorded by the Extreme-ultraviolet Imaging Spectrometer (EIS) on the Hinode spacecraft. The observed Ar xiv/Ca xiv ratio yields an argon/calcium abundance ratio seven times greater than expected from the photospheric abundance. Such a large abundance anomaly is unprecedented in the solar atmosphere. We interpreted this result as being due to an inverse first ionization potential (FIP) effect. In the published work, two lines of Ar xiv were observed, and one line was tentatively identified as an Ar xi line. In this paper, we report observing a similar enhancement in a full-CCD EIS flare spectrum in 13 argon lines that lie within the EIS wavelength ranges. The observed lines include two Ar xi lines, four Ar xiii lines, six Ar xiv lines, and one Ar xv line. The enhancement is far less than reported in Doschek et al. but exhibits similar morphology. The argon abundance is close to a photospheric abundance in the enhanced area, and the abundance could be photospheric. This enhancement occurs in association with a sunspot in a small area only a few arcseconds (1″ = about 700 km) in size. There is no enhancement effect observed in the normally high-FIP sulfur and oxygen line ratios relative to lines of low-FIP elements available to EIS. Calculations of path lengths in the strongest enhanced area in Doschek et al. indicate a depletion of low-FIP elements.

Quantum Stark broadening of Ar XV lines. Strong collision and quadrupolar potential contributions

We present in this paper electron impact broadening for six Ar XV lines using our quantum mechanical formalism and the semiclassical perturbation one. Additionally, our calculations of the corresponding atomic structure data (energy levels and oscillator strengths) and collision strengths are given as well. The lines considered here are divided into two sets: a first set of four lines involving the ground level: 1s22s21S0– 1s22snp 1P1o where 2⩽n⩽5 and a second set of two lines involving excited levels: 1s22s2p 1P1o–1s22s3s 1S0 and 1s22s2p 3P0o–1s22s3s 3S1. An extensive comparison between the quantum and the semiclassical results was performed in order to analyze the reason for differences between quantum and semiclassical results up to the factor of two. It has been shown that the difference between the two results may be due to the evaluation of strong collision contributions by the semiclassical formalism. Except few semiclassical results, the present results are the first to be published. After the recent discovery of the far UV lines of Ar VII in the spectra of very hot central stars of planetary nebulae and white dwarfs, the present -and may be further- results can be used also for the corresponding future spectral analysis.

Energy Levels and Observed Spectral Lines of Ionized Argon, ArII through ArXVIII

The energy levels and observed spectral lines of ionized argon atoms, in all stages of ionization, have been compiled. Sufficient experimental data were found to generate level and line tables for ArII through ArXV. For ArXVI a mix of experimental and theoretical data were used. Because of the superiority of the theoretical data for ArXVII and ArXVIII, theoretical values are compiled for the energy levels and the lines are calculated from them. Experimental g-factors are included for ArII. A value, either experimental, semiempirical, or theoretical, is included for the ionization energy of each ion.

Calcium‐to‐Argon and Nickel‐to‐Argon Abundance Ratios as Tracers of the Source Region of Postflare Loop System Material

Intensities of abundance diagnostic lines of Ca XV, Ca XVI, Ni XVII, Ar XIII, and Ar XV have been derived for a classic flare loop system observed during the Skylab mission. These have been used to test for photospheric or coronal origin of the flare loop material. The resulting FIP-bias factors are between 1.7 and 4.6 with a majority of the values around 4.5 indicating a source with material modified by the FIP effect. The loop system bias factors are similar to those observed in a sample of Skylab prominences, suggesting that the disrupted mass of the preflare embedded filament provided the loop system material.

Atomic data and spectral line intensities for Ar XV

Electron impact collision strengths, energy levels, oscillator strengths, and spontaneous radiative decay rates are calculated for Ar XV. The configurations used are 2 s 2 , 2 s 2 p , 2 p 2 , 2 l 3 l ′ , 2 l 4 l ′ and 2 s 5 l ′ , with l = s,p and l ′ = s,p,d giving rise to 92 fine-structure levels in intermediate coupling. Collision strengths are calculated at eight incident energies (10, 20, 30, 60, 120, 180, 240, and 300 Ry) for transitions within the three lowest configurations, and five incident energies (60, 120, 180, 240, and 300 Ry) for transitions between the lowest five levels and the n = 3, 4, 5 configurations, using the distorted wave approximation. Excitation rate coefficients are calculated as a function of electron temperature by assuming a Maxwellian electron velocity distribution. Using the excitation rate coefficients and the radiative transition rates of the present work, and R-matrix results for the 2s 2, 2s2p, 2p 2 configurations available in the literature, statistical equilibrium equations for level populations are solved at electron densities covering the range of 10 8–10 14 cm −3 at an electron temperature of log T e ( K ) = 6.6 , corresponding to the maximum abundance of Ar XV. Spectral line intensities are calculated, and their diagnostic relevance is discussed. Observed line ratios indicate electron temperatures of the relevant emitting plasma close to log T e ( K ) = 6.6 . This dataset will be made available in the next version of the CHIANTI database.

Energy levels and radiative rates for transitions in Ar XIII, Ar XIV and Ar XV

Energies for 524 levels of Ar XIII, 460 levels of Ar XIV and 156 levels of Ar XV have been calculated using the  code of Dyall et al. (1989). Additionally, radiative rates, oscillator strengths, and line strengths are calculated for all electric dipole (E1), magnetic dipole (M1), electric quadrupole (E2), and magnetic quadrupole (M2) transitions among these levels. Comparisons are made with the limited results available in the literature, and the accuracy of the data is assessed. Our energy levels are estimated to be accurate to better than 1%, whereas results for other parameters are probably accurate to better than 20%. Additionally, the level lifetimes derived from our radiative rates are in excellent agreement with measured values.

High-precision measurements in few-electron highly charged ions at the HeidelbergElectron Beam Ion Trap (EBIT)

The research program at the Heidelberg Electron Beam Ion Trap (EBIT) has concentrated mainly on precision measurements relevant to quantum electrodynamics (QED) and nuclear physics. Spectroscopic measurements in the optical region have delivered the most accurate wavelengths ever reported for highly charged ions, extracting even isotopic shifts. The forbidden transitions of B-like Ar XIV and Be-like Ar XV ions were studied. They are especially interesting, since the QED contributions are as large as 0.2%. Improved atomic structure calculations allowed for the determination of their values with growing accuracy. The lifetimes of the corresponding metastable levels have also been measured with an uncertainty of less than 0.5% thus becoming sensitive to the influence of the bound electron anomalous magnetic moment, so far an almost experimentally unexplored QED effect. A new laser spectroscopic setup aims at facilitating future studies of the hyperfine structure of heavy hydrogenic ions. Through the study of the dielectronic recombination, information on rare processes, such as two-electron-one-photon transitions in Ar16+, or the interference effects between dielectronic and radiative recombination in Hg77+, and accurate values for the excitation energies of very heavy HCI have been obtained. A novel X-ray crystal spectrometer allowing absolute X-ray wavelength measurements in the range up to 15 keV with very high precision and reproducibility is currently used to study the Lyman series of H-like ions of medium-Z ions and the 2s–2p transitions of very heavy Li-like ions. PACS Nos.: 31.30.Jv, 32.80.Fb, 32.80.Dz, 32.30.Jv, 32.30.Rj, 95.30.Dr

Identification of Three Weak Lines and Their Influences onDiagnostics of Electron Temperature and Density in Astrophysical Plasmas

By comparing of the spectra from the Chandra LETGs observation with thesynthetic spectra of argon, we identify two weak emission lines, thatis, the Ar XV 27.470 A line with transition2s3p 1P1−2s2 1S0 and the Ar XVI 27.872 A line withtransition 3d 2D3/2−2p 2P1/2, which blend with the NVII Lyα emission line. Severalsecond-order spectral lines are also identified, one of which isthe second-order Fe XVIII 14.534 A line withtransition 2p4(3P)3d 2F5/2−2p5 2P3/2, whichblends with theinter-combination line of He-like N VI. In order to study the effects ofthese new identified weak lines on the electron temperature anddensity, we diagnose the two parameters using the intensity ratioof triplets of the He-like N VI and that of resonance lines of H-and He-like N. In the literature, there is a discrepancy of thetemperatures deduced from N VI from other He-like ions, suchas C V and O VII. The discrepancy disappears after thecontribution of these weak lines is taken into account.

Identification and analysis of soft X-ray lines of Ar xiii-Ar xvi in laboratory and astrophysical plasmas

The emission‐line spectrum of an argon plasma in the soft X‐ray region 20–30 Å is simulated using our calculated atomic data. The atomic data, including energy levels, spontaneous radiative decay rates and effective collision strengths, are obtained by the Flexible Atomic Code recently developed by Gu. Good agreement is found between the theoretical and experimental emission spectra. All strong lines observed in the experiment have been identified. Compared with previous theoretical results, the predicted intensity for the line located at 27.631 Å from the 3d–2p transition of Ar xiv is dramatically reduced, resulting in a better agreement with experiment. Some weak lines are also identified in this work. In order to simulate the experimental spectra, the electron density and temperature are required. We choose density‐ and temperature‐sensitive lines to determine these quantities. Reliable results for the electron density around 8.7 × 1010 cm−3 and electron temperature around 2.4 × 106 K have been obtained. The present atomic data can also be used to identify the emission lines of astrophysical plasmas. As an example, some lines belonging to Ar ions are identified for the first time by comparing the spectra from Chandra LETG observation of Capella with the synthetic spectra. The line located at 27.018 Å, which was originally assigned to C vi (Lyγ), should be attributed to Ar xv from the present work. The line at 28.336 Å is also identified for the first time as the 3s–2p transition of Ar xv.

High precision wavelength measurements of QED-sensitive forbidden transitions in highly charged argon ions.

We present the results of an experimental study of magnetic dipole (M1) transitions in highly charged argon ions (Ar X, Ar XI, Ar XIV, Ar XV) in the visible spectral range using an electron beam ion trap. Their wavelengths were determined with, for highly charged ions, unprecedented accuracy up to the sub-ppm level and compared with theoretical calculations. The QED contributions, calculated in this Letter, are found to be 4 orders of magnitude larger than the experimental error and are absolutely indispensable to bring theory and experiment to a good agreement. This method shows great potential for the study of QED effects in relativistic few-electron systems.

Experimental and simulatedargon spectra in the 2.3-3.4 nm region from tokamak plasmas

Experimental argon spectra in the 2.3-3.4 nm region from the Jettokamak on a single null divertor configuration have been simulated. Thespectra include lines from five ionization states, namely from Ar15+Li-like to Ar11+ N-like ions. Collisional-radiative models have beenconstructed for these five Ar ions, considering electron collisionalexcitation and radiative decay as the populating processes of the excitedstates. These models give photon emission coefficients for the emittedlines at electron density and temperature values corresponding to theexperimental situations. Impurity modelling is performed using aone-dimensional (1D) impurity transport code, calculating thesteady-state radial distribution of the Ar ions. The Ar line brightnessesare evaluated in a post-processing subroutine and simulated spectra areobtained. The parts of the spectra corresponding to a single-ionizationstate do not depend on the experimental conditions and show goodagreement except for the amplitude of the simulated 2s-3p Ar XVIline and the shape of the simulated 2.50 nm feature (composed of Ar XVI and Ar XV lines). On the other hand, the superpositionof these spectra depends on the experimental conditions, as aconsequence of the fact that the ion charge distributiondepends not only on the radial profiles of the electrondensity and temperature, but also of the impurity transportcoefficients. Simulations of the Ar spectra (includingtransport) give confidence in the atomic physics calculations;moreover, they allow the determination of the transportcoefficients in the plasma region emitting the consideredionization states, i.e. at the interior of the last closedmagnetic surface (LCMS). For a correct simulation of theamplitudes of the spectral features it is necessary to includea transport barrier inside the LCMS. As far as the atomicphysics is concerned, we report improved wavelengths forAr XV transitions and we benchmark photon emissioncoefficients for XUV transitions in highly ionizedargon.

Experimental M1 Transition Rates of Coronal Lines from Arx, Arxiv, and Arxv

Transition probabilities of three magnetic dipole (M1) transitions in multiply charged ions of Ar have been measured using the Livermore electron-beam ion trap. Two of the transitions are in the ground con—gurations of Ar XIV (B-like) and Ar IX (F-like), and are associated with the coronal lines at 4412.4 and 5533.4 respectively. The third is in the excited 2s2p con—guration of Be-like Ar XV and produces Ae , the coronal line at 5943.73 Our results for the three atomic level lifetimes are 9.32 ^ 0.12 ms for the Ae . Ar X 2s22p5 level, 9.70 ^ 0.15 ms for the Ar XIV 2s22p level, and 15.0 ^ 0.8 ms for the Ar XV 2P 1@2 2P 3@2 2s2p level. These results diUer signi—cantly from earlier measurements and are the most accurate 3P 2 ones to date. Subject headings: atomic datamethods: laboratory

Precision and accuracy of lifetimes of metastable levels using the Kingdon trap technique

The accuracy of measurements of the lifetimes of metastable levels using a Kingdon ion trap technique is discussed with reference to the recent measurement of the transition rate from the excited 2 s2 p 3 P 2 level of AR XV. Particular attention focused on the aspects of the Kingdon trap technique, which differed from competing alternatives and might apply differently to ground and excited terms. These differences are related to the corrections for quenching of the metastable level by ion–atom collisions, to the possible quenching by Stark mixing due to the higher electric field of the Kingdon trap, and to optical effects associated with the charging of a lens in the light collection system. No significant systematic corrections to present excited level measurements were identified.

CROSS SECTIONS AND RATE COEFFICIENTS FOR EXCITATION OF THE 1s22s2p3PoJ→ 1s22s2p3PoJ′FINE-STRUCTURE TRANSITIONS IN BERYLLIUM-LIKE IONS BY HEAVY PARTICLE IMPACT

Cross sections for excitation of the 1s22s2p3PoJ→ 1s22s2p3PoJ′fine-structure transitions in beryllium-like ions by proton, deuteron, triton, and α-particle impact have been calculated using a close-coupled impact-parameter method. This technique includes the effects of dipole coupling to the nearby triplet 2p2, 2s3s, and 2s3dconfigurations by means of a polarization potential. We consider the ions C III, N IV, O V, Ne VII, Mg IX, Al X, Si XI, S XIII, Ar XV, Ca XVII, Ti XIX, Cr XXI, Fe XXIII, and Ni XXV. Excitation rate coefficients have also been calculated from the cross sections for a range of temperatures.

Magnetic dipole transition rates from measured lifetimes of levels of Be-like and B-like argon ions

The lifetimes of the ${1s}^{2}2s2p{}^{3}{P}_{2}$ level of Ar XV and ${1s}^{2}{2s}^{2}2p{}^{2}{P}_{3/2}$ of Ar XIV have been measured using metastable ${\mathrm{Ar}}^{14+}$ and ${\mathrm{Ar}}^{13+}$ ions produced by an electron cyclotron resonance ion source, which were subsequently separately captured into a Kingdon ion trap. The lifetime results are \ensuremath{\tau}(Ar XV, 2s2p ${}^{3}{P}_{2})=13.4(7)\mathrm{ms}$ and \ensuremath{\tau}(Ar XIV,$2p{}^{2}{P}_{3/2})=9.12(18)\mathrm{ms}.$ Transition rates derived from the measured lifetimes differ significantly from both relativistic and nonrelativistic calculations of the $2s2p{}^{3}{P}_{1}{--}^{3}{P}_{2}$ $M1$ transition rate of Ar XV, but are in reasonable agreement with calculations for the $2p{}^{2}{P}_{1/2}{--}^{2}{P}_{3/2}$ $M1$ rate of Ar XIV.

Cross Sections and Rate Coefficients for Excitation of Δ n = 0 Transitions in Be-Like Ions with 6 ≤ Z ≤ 54

Excitation cross sections and rate coefficients by electron impact are calculated for the transitions among the 1 s 22 s 2, 1 s 22 s2 p, 1 s 22 p 2 levels of the Be-like ions C III, O V, Ne VII, Mg IX, Si XI, S XIII, Ar XV, Ca XVII, Ti XIX, Fe XXIII, Zn XXVII, Kr XXXIII, Mo XXXIX, and Xe LI by a Coulomb-Born approximation with exchange and including relativistic effects and configuration interactions. The cross-section and rate coefficient data are fitted by simple functions of the (scaled) electron impact energy and temperature, respectively. Level energies, mixing coefficients, and transition wavelengths and probabilities are also given.

Beam-foil spectroscopy in the extreme UV of highly ionized silicon Si XI and the isoelectronic ions AI X, S XIII and Ar XV

Spectra of highly-ionized silicon, aluminium, sulfur and argon ions produced by the beam-foil technique have been analysed in the 5-40 nm wavelength range. Numerous transitions belonging to n = 3-4, 4-5 and 3-5 transitions arrays in the beryllium-like spectra Al X, Si XI, S XIII and Ar XV were observed for the first time. The assignment of spectral lines was corroborated by comparison along the isoelectronic sequence.

Atomic data for opacity calculations. XIV. The beryllium sequence

The authors have calculated 1814 energy levels in LS coupling, 33030 oscillator strengths and 859570 photoionization cross section values for the following fifteen members of the beryllium isoelectronic sequence: Be I, B II, C III, N IV, O V, F VI, Ne VII, Na VIII, Mg IX, Al X, Si XI, S XIII, Ar XV, Ca XVII and Fe XXIII. Photoionization is from 1554 bound states lying below the 2s ionization thresholds. The continua are perturbed by resonances converging onto the 2p, 3s, 3p and 3d states of the residual Li-like ions. They delineate the resulting autoionization features by using sufficiently small energy step lengths in regions where the cross sections vary rapidly. Photoexcitation of the core produces large PEC resonances which dominate photoionization of Be I and the less highly ionized ions. They discuss some selected examples drawn from the entire data set and make comparisons with the work of other investigators.