Atoms
http://www.mdpi.com/journal/atoms
Latest open access articles published in Atoms at http://www.mdpi.com/journal/atoms<![CDATA[Atoms, Vol. 2, Pages 334-356: Spectral-Kinetic Coupling and Effect of Microfield Rotation on Stark Broadening in Plasmas]]>
http://www.mdpi.com/2218-2004/2/3/334
The study deals with two conceptual problems in the theory of Stark broadening by plasmas. One problem is the assumption of the density matrix diagonality in the calculation of spectral line profiles. This assumption is closely related to the definition of zero wave functions basis within which the density matrix is assumed to be diagonal, and obviously violated under the basis change. A consistent use of density matrix in the theoretical scheme inevitably leads to interdependence of atomic kinetics, describing the population of atomic states with the Stark profiles of spectral lines, i.e., to spectral-kinetic coupling. The other problem is connected with the study of the influence of microfield fluctuations on Stark profiles. Here the main results of the perturbative approach to ion dynamics, called the theory of thermal corrections (TTC), are presented, within which the main contribution to effects of ion dynamics is due to microfield fluctuations caused by rotations. In the present study the qualitative behavior of the Stark profiles in the line center within predictions of TTC is confirmed, using non-perturbative computer simulations.Atoms2014-07-3023Article10.3390/atoms20303343343562218-20042014-07-30doi: 10.3390/atoms2030334Alexander DemuraEvgeny Stambulchik<![CDATA[Atoms, Vol. 2, Pages 319-333: Line-Shape Code Comparison through Modeling and Fitting of Experimental Spectra of the C ii 723-nm Line Emitted by the Ablation Cloud of a Carbon Pellet]]>
http://www.mdpi.com/2218-2004/2/3/319
Various codes of line-shape modeling are compared to each other through the profile of the C ii 723-nm line for typical plasma conditions encountered in the ablation clouds of carbon pellets, injected in magnetic fusion devices. Calculations were performed for a single electron density of 1017 cm−3 and two plasma temperatures (T = 2 and 4 eV). Ion and electron temperatures were assumed to be equal (Te = Ti = T). The magnetic field, B, was set equal to either to zero or 4 T. Comparisons between the line-shape modeling codes and two experimental spectra of the C ii 723-nm line, measured perpendicularly to the B-field in the Large Helical Device (LHD) using linear polarizers, are also discussed.Atoms2014-07-1423Article10.3390/atoms20303193193332218-20042014-07-14doi: 10.3390/atoms2030319Mohammed KoubitiMotoshi GotoSandrine FerriStephanie HansenEvgeny Stambulchik<![CDATA[Atoms, Vol. 2, Pages 299-318: Ion Dynamics Effect on Stark-Broadened Line Shapes: A Cross-Comparison of Various Models]]>
http://www.mdpi.com/2218-2004/2/3/299
Modeling the Stark broadening of spectral lines in plasmas is a complex problem. The problem has a long history, since it plays a crucial role in the interpretation of the observed spectral lines in laboratories and astrophysical plasmas. One difficulty is the characterization of the emitter’s environment. Although several models have been proposed over the years, there have been no systematic studies of the results, until now. Here, calculations from stochastic models and numerical simulations are compared for the Atoms 2014, 2 300 Lyman-α and -β lines in neutral hydrogen. Also discussed are results from the Helium-α and -β lines of Ar XVII.Atoms2014-07-0423Article10.3390/atoms20302992993182218-20042014-07-04doi: 10.3390/atoms2030299Sandrine FerriAnnette CalistiCaroline MosséJoël RosatoBernard TalinSpiros AlexiouMarco GigososManuel GonzálezDiego González-HerreroNatividad LaraThomas GomezCarlos IglesiasSonja LorenzenRoberto ManciniEvgeny Stambulchik<![CDATA[Atoms, Vol. 2, Pages 277-298: Spectral Line Shapes of He I Line 3889 Å]]>
http://www.mdpi.com/2218-2004/2/2/277
Spectral line shapes of neutral helium 3889 Å(23S–33P) transition line are calculated by using several theoretical methods. The electronic contribution to the line broadening is calculated from quantum statistical many-particle theory by using thermodynamic Green's function, including dynamic screening of the electron-atom interaction. The ionic contribution is taken into account in a quasistatic approximation, where a static microfield distribution function is presented. Strong electron collisions are consistently considered with an effective two-particle T-matrix approach, where Convergent Close Coupling method gives scattering amplitudes including Debye screening for neutral helium. Then the static profiles converted to dynamic profiles by using the Frequency Fluctuation Model. Furthermore, Molecular Dynamics simulations for interacting and independent particles are used where the dynamic sequence of microfield is taken into account. Plasma parameters are diagnosed and good agreements are shown by comparing our theoretical results with the recent experimental result of Jovićević et al. (J. Phys. B: At. Mol. Opt. Phys. 2005, 38, 1249). Additionally, comparison with various experimental data in a wide range of electron density ne ≈ (1022− 1024)m−3 and temperature T ≈ (2−6) × 104 K are presented.Atoms2014-06-2322Article10.3390/atoms20202772772982218-20042014-06-23doi: 10.3390/atoms2020277Banaz OmarManuel GonzálezMarco GigososTlekkabul RamazanovMadina JelbuldinaKarlygash DzhumagulovaMark ZammitDmitry FursaIgor Bray<![CDATA[Atoms, Vol. 2, Pages 259-276: Influence of Microfield Directionality on Line Shapes]]>
http://www.mdpi.com/2218-2004/2/2/259
In the framework of the Spectral Line Shapes in Plasmas Code Comparison Workshop (SLSP), large discrepancies appeared between the different approaches to account for ion motion effects in spectral line shape calculations. For a better understanding of these effects, in the second edition of the SLSP in August, 2013, two cases were dedicated to the study of the ionic field directionality on line shapes. In this paper, the effects of the direction and magnitude fluctuations are separately analyzed. The effects of two variants of electric field models, (i) a pure rotating field with constant magnitude and (ii) a time-dependent magnitude field in a given direction, together with the effects of the time-dependent ionic field on shapes of the He II Lyman-α and -β lines for different densities and temperatures, are discussed.Atoms2014-06-1922Article10.3390/atoms20202592592762218-20042014-06-19doi: 10.3390/atoms2020259Annette CalistiAlexander DemuraMarco GigososDiego González-HerreroCarlos IglesiasValery LisitsaEvgeny Stambulchik<![CDATA[Atoms, Vol. 2, Pages 253-258: Ideal Coulomb Plasma Approximation in Line Shape Models: Problematic Issues]]>
http://www.mdpi.com/2218-2004/2/2/253
In weakly coupled plasmas, it is common to describe the microfield using a Debye model. We examine here an “artificial” ideal one-component plasma with an infinite Debye length, which has been used for the test of line shape codes. We show that the infinite Debye length assumption can lead to a misinterpretation of numerical simulations results, in particular regarding the convergence of calculations. Our discussion is done within an analytical collision operator model developed for hydrogen line shapes in near-impact regimes. When properly employed, this model can serve as a reference for testing the convergence of simulations.Atoms2014-06-1922Article10.3390/atoms20202532532582218-20042014-06-19doi: 10.3390/atoms2020253Joel RosatoHubert CapesRoland Stamm<![CDATA[Atoms, Vol. 2, Pages 225-252: Widths and Shifts of Isolated Lines of Neutral and Ionized Atoms Perturbed by Collisions With Electrons and Ions: An Outline of the Semiclassical Perturbation (SCP) Method and of the Approximations Used for the Calculations]]>
http://www.mdpi.com/2218-2004/2/2/225
“Stark broadening” theory and calculations have been extensively developed for about 50 years. The theory can now be considered as mature for many applications, especially for accurate spectroscopic diagnostics and modeling, in astrophysics, laboratory plasma physics and technological plasmas, as well. This requires the knowledge of numerous collisional line profiles. In order to meet these needs, the “SCP” (semiclassical perturbation) method and numerical code were created and developed. The SCP code is now extensively used for the needs of spectroscopic diagnostics and modeling, and the results of the published calculations are displayed in the STARK-B database. The aim of the present paper is to introduce the main approximations leading to the impact of semiclassical perturbation method and to give formulae entering the numerical SCP code, in order to understand the validity conditions of the method and of the results; and also to understand some regularities and systematic trends. This would also allow one to compare the method and its results to those of other methods and codes. 1Atoms2014-06-1022Article10.3390/atoms20202252252522218-20042014-06-10doi: 10.3390/atoms2020225Sylvie Sahal-BréchotMilan DimitrijevićNabil Nessib<![CDATA[Atoms, Vol. 2, Pages 215-224: Validation and Implementation of Uncertainty Estimates of Calculated Transition Rates]]>
http://www.mdpi.com/2218-2004/2/2/215
Uncertainties of calculated transition rates in LS-allowed electric dipole transitions in boron-like O IV and carbon-like Fe XXI are estimated using an approach in which differences in line strengths calculated in length and velocity gauges are utilized. Estimated uncertainties are compared and validated against several high-quality theoretical data sets in O IV, and implemented in large scale calculations in Fe XXI.Atoms2014-05-1522Review10.3390/atoms20202152152242218-20042014-05-15doi: 10.3390/atoms2020215Jörgen EkmanMichel GodefroidHenrik Hartman<![CDATA[Atoms, Vol. 2, Pages 207-214: Electron-Impact Widths and Shifts of B III 2p-2s Lines]]>
http://www.mdpi.com/2218-2004/2/2/207
In this paper, we present results for the relativistic quantum mechanical calculations of electron-impact line widths and shifts of 2p-2s transitions in doubly ionized boron (B III) ions. We use the Dirac R-matrix methods to solve (N + 1)-electron colliding systems for the scattering matrices that are required. The line widths are calculated for an electron density 1:81 × 1018 cm-3 and electron temperature 10:6 eV. The obtained results agree well with all the semiempirical calculations and most of the semiclassical calculations, and are closer to the experimental results published by Glenzer and Kunze (Glenzer, S.; Kunze, H.-J. Stark broadening of resonance transitions in B III. Phys. Rev. A 1996, 53, 2225–2229). Our line widths are almost twice as large as the earlier quantum mechanical calculations for the set of particular plasma conditions.Atoms2014-05-1522Article10.3390/atoms20202072072142218-20042014-05-15doi: 10.3390/atoms2020207Bin DuanMuhammad BariZeqing WuJun Yan<![CDATA[Atoms, Vol. 2, Pages 195-206: Hydrogen Spectral Line Shape Formation in the SOL of Fusion Reactor Plasmas]]>
http://www.mdpi.com/2218-2004/2/2/195
The problems related to the spectral line-shape formation in the scrape of layer (SOL) in fusion reactor plasma for typical observation chords are considered. The SOL plasma is characterized by the relatively low electron density (1012–1013 cm−3) and high temperature (from 10 eV up to 1 keV). The main effects responsible for the line-shape formation in the SOL are Doppler and Zeeman effects. The main problem is a correct modeling of the neutral atom velocity distribution function (VDF). The VDF is determined by a number of atomic processes, namely: molecular dissociation, ionization and charge exchange of neutral atoms on plasma ions, electron excitation accompanied by the charge exchange from atomic excited states, and atom reflection from the wall. All the processes take place step by step during atom motion from the wall to the plasma core. In practice, the largest contribution to the neutral atom radiation emission comes from a thin layer near the wall with typical size 10–20 cm, which is small as compared with the minor radius of modern devices including international test experimental reactor ITER (radius 2 m). The important problem is a strongly non-uniform distribution of plasma parameters (electron and ion densities and temperatures). The distributions vary for different observation chords and ITER operation regimes. In the present report, most attention is paid to the problem of the VDF calculations. The most correct method for solving the problem is an application of the Monte Carlo method for atom motion near the wall. However, the method is sometimes too complicated to be combined with other numerical codes for plasma modeling for various regimes of fusion reactor operation. Thus, it is important to develop simpler methods for neutral atom VDF in space coordinates and velocities. The efficiency of such methods has to be tested via a comparison with the Monte Carlo codes for particular plasma conditions. Here a new simplified method for description of neutral atoms penetration into plasma is suggested. The method is based on the ballistic motion of neutrals along the line-of-sight (LoS) in the forward–back approximation. As a result, two-dimensional distribution functions, dependent on the LoS coordinate and the velocity projection on the LoS, and responsible for the Doppler broadening of the line shape, are calculated. A comparison of the method with Monte Carlo calculations allows the evaluation of the accuracy of the ballistic model. The Balmer spectral line shapes are calculated for specific LoS typical for ITER diagnostics.Atoms2014-05-1522Review10.3390/atoms20201951952062218-20042014-05-15doi: 10.3390/atoms2020195Valery LisitsaMikhail KadomtsevVladislav KotovVladislav NeverovVladimir Shurygin<![CDATA[Atoms, Vol. 2, Pages 178-194: Review of Langmuir-Wave-Caused Dips and Charge-Exchange-Caused Dips in Spectral Lines from Plasmas and their Applications]]>
http://www.mdpi.com/2218-2004/2/2/178
We review studies of two kinds of dips in spectral line profiles emitted by plasmas—dips that have been predicted theoretically and observed experimentally: Langmuir-wave-caused dips (L-dips) and charge-exchange-caused dips (X-dips). There is a principal difference with respect to positions of L-dips and X-dips relative to the unperturbed wavelength of a spectral line: positions of L-dips scale with the electron density Ne roughly as Ne1/2, while positions of X-dips are almost independent of Ne (the dependence is much weaker than for L-dips). L-dips and X-dips phenomena are important, both fundamentally and practically. The fundamental importance is due to a rich physics behind each of these phenomena. L-dips are a multi-frequency resonance phenomenon caused by a single-frequency (monochromatic) electric field. X-dips are due to charge exchange at anticrossings of terms of a diatomic quasi-molecule, whose nuclei have different charges. As for important practical applications, they are as follows: observations of L-dips constitute a very accurate method to measure the electron density in plasmas—a method that does not require knowledge of the electron temperature. L-dips also allow measuring the amplitude of the electric field of Langmuir waves—the only spectroscopic method available for this purpose. Observations of X-dips provide an opportunity to determine rate coefficient of charge exchange between multi-charged ions. This is an important reference data, virtually inaccessible by other experimental methods. The rate coefficients of charge exchange are important for magnetic fusion in Tokamaks, for population inversion in the soft x-ray and VUV ranges, for ion storage devices, as well as for astrophysics (e.g., for the solar plasma and for determining the physical state of planetary nebulae).Atoms2014-05-1322Review10.3390/atoms20201781781942218-20042014-05-13doi: 10.3390/atoms2020178Elisabeth DalimierEugene OksOldrich Renner<![CDATA[Atoms, Vol. 2, Pages 157-177: The Second Workshop on Lineshape Code Comparison: Isolated Lines]]>
http://www.mdpi.com/2218-2004/2/2/157
In this work, we briefly summarize the theoretical aspects of isolated line broadening. We present and discuss test run comparisons from different participating lineshape codes for the 2s-2p transition for LiI, B III and NV.Atoms2014-05-1222Article10.3390/atoms20201571571772218-20042014-05-12doi: 10.3390/atoms2020157Spiros AlexiouMilan DimitrijevićSylvie Sahal-BrechotEvgeny StambulchikBin DuanDiego González-HerreroMarco Gigosos<![CDATA[Atoms, Vol. 2, Pages 123-156: AtomPy: An Open Atomic Data Curation Environment for Astrophysical Applications]]>
http://www.mdpi.com/2218-2004/2/2/123
We present a cloud-computing environment, referred to as AtomPy, based on Google-Drive Sheets and Pandas (Python Data Analysis Library) DataFrames to promote community-driven curation of atomic data for astrophysical applications, a stage beyond database development. The atomic model for each ionic species is contained in a multi-sheet workbook, tabulating representative sets of energy levels, A-values and electron impact effective collision strengths from different sources. The relevant issues that AtomPy intends to address are: (i) data quality by allowing open access to both data producers and users; (ii) comparisons of different datasets to facilitate accuracy assessments; (iii) downloading to local data structures (i.e., Pandas DataFrames) for further manipulation and analysis by prospective users; and (iv) data preservation by avoiding the discard of outdated sets. Data processing workﬂows are implemented by means of IPython Notebooks, and collaborative software developments are encouraged and managed within the GitHub social network. The facilities of AtomPy are illustrated with the critical assessment of the transition probabilities for ions in the hydrogen and helium isoelectronic sequences with atomic number Z ≤ 10.Atoms2014-05-0222Article10.3390/atoms20201231231562218-20042014-05-02doi: 10.3390/atoms2020123Claudio MendozaJosiah BoswellDavid AjokuManuel Bautista<![CDATA[Atoms, Vol. 2, Pages 86-122: Assessing Uncertainties of Theoretical Atomic Transition Probabilities with Monte Carlo Random Trials]]>
http://www.mdpi.com/2218-2004/2/2/86
This paper suggests a method of evaluation of uncertainties in calculated transition probabilities by randomly varying parameters of an atomic code and comparing the results. A control code has been written to randomly vary the input parameters with a normal statistical distribution around initial values with a certain standard deviation. For this particular implementation, Cowan’s suite of atomic codes (R.D. Cowan, The Theory of Atomic Structure and Spectra, Berkeley, CA: University of California Press, 1981) was used to calculate radiative rates of magnetic-dipole and electric-quadrupole transitions within the ground configuration of titanium-like iron, Fe V. The Slater parameters used in the calculations were adjusted to fit experimental energy levels with Cowan’s least-squares fitting program, RCE. The standard deviations of the fitted parameters were used as input of the control code providing the distribution widths of random trials for these parameters. Propagation of errors through the matrix diagonalization and summation of basis state expansions leads to significant variations in the resulting transition rates. These variations vastly differ in their magnitude for different transitions, depending on their sensitivity to errors in parameters. With this method, the rate uncertainty can be individually assessed for each calculated transition.Atoms2014-04-1422Article10.3390/atoms2020086861222218-20042014-04-14doi: 10.3390/atoms2020086Alexander Kramida<![CDATA[Atoms, Vol. 2, Pages 15-85: Critical Assessment of Theoretical Calculations of Atomic Structure and Transition Probabilities: An Experimenter’s View]]>
http://www.mdpi.com/2218-2004/2/1/15
The interpretation of atomic observations by theory and the testing of computational predictions by experiment are interactive processes. It is necessary to gain experience with “the other side” before claims of achievement can be validated and judged. The discussion covers some general problems in the field as well as many specific examples, mostly organized by isoelectronic sequence, of what level of accuracy recently has been reached or which atomic structure or level lifetime problem needs more attention.Atoms2014-03-1921Article10.3390/atoms201001515852218-20042014-03-19doi: 10.3390/atoms2010015Elmar Träbert<![CDATA[Atoms, Vol. 2, Pages 1-14: Evaluation and Comparison of the Configuration Interaction Calculations for Complex Atoms]]>
http://www.mdpi.com/2218-2004/2/1/1
Configuration interaction (CI) methods are the method of choice for the determination of wave functions for complex atomic systems from which a variety of atomic properties may be computed. When applied to highly ionized atoms, where few, if any, energy levels from observed wavelengths are available, the question arises as to how a calculation may be evaluated. Many different codes are available for such calculations. Agreement between the results from different codes in itself is not a check on accuracy, but may be due to a similarity in the computational procedures. This paper reviews basic theory, which, when applied in a systematic manner, can be the basis for the evaluation of accuracy. Results will be illustrated in the study of 4s24p5 (odd) and 4s24p44d (even) levels in W39+ and the transitions between them.Atoms2014-03-1921Article10.3390/atoms20100011142218-20042014-03-19doi: 10.3390/atoms2010001Charlotte Fischer<![CDATA[Atoms, Vol. 1, Pages 14-16: Notes on Critical Assessment of Theoretical Calculations of Atomic Structure and Transition Probabilities]]>
http://www.mdpi.com/2218-2004/1/3/14
Atomic structure and transition probabilities are fundamental physical data required in many fields of science and technology. Atomic physics codes are freely available to other community users to generate atomic data for their interest, but the quality of these data is rarely verified. This special issue addresses estimation of uncertainties in atomic structure and transition probability calculations, and discusses methods and strategies to assess and ensure the quality of theoretical atomic data.Atoms2013-08-0813Editorial10.3390/atoms103001414162218-20042013-08-08doi: 10.3390/atoms1030014Hyun-Kyung ChungPer JönssonAlexander Kramida<![CDATA[Atoms, Vol. 1, Pages 13: Special Issue on Critical Assessment of Theoretical Calculations of Atomic Structure and Transition Probabilities]]>
http://www.mdpi.com/2218-2004/1/2/13
There exist several codes in the atomic physics community to generate atomic structure and transition probabilities freely and readily distributed to researchers outside atomic physics community, in plasma, astrophysical or nuclear physics communities. Users take these atomic physics codes to generate the necessary atomic data or modify the codes for their own applications. However, there has been very little effort to validate and verify the data sets generated by non-expert users. [...]Atoms2013-06-2112Editorial10.3390/atoms102001313132218-20042013-06-21doi: 10.3390/atoms1020013Per JönssonHyun-Kyung Chung<![CDATA[Atoms, Vol. 1, Pages 2-12: Emission of β+ Particles Via Internal Pair Production in the 0+ – 0+ Transition of 90Zr: Historical Background and Current Applications in Nuclear Medicine Imaging]]>
http://www.mdpi.com/2218-2004/1/1/2
90Y is traditionally considered as a pure β– emitter. However, the decay of this radionuclide has a minor branch to the 0+ first excited state of 90Zr at 1.76 MeV, that is followed by a β+/β– emission. This internal pair production has been largely studied in the past because it is generated by a rare electric monopole transition (E0) between the states 0+/0+ of 90Zr. The positronic emission has been recently exploited for nuclear medicine applications, i.e. positron emission tomography (PET) acquisitions of 90Y-labelled radiopharmaceuticals, widely used as therapeutic agents in internal radiation therapy. To date, this topic is gaining increasing interest in the radiation dosimetry community, as the possibility of detecting β+ emissions from 90Y by PET scanners may pave the way for an accurate patient-specific dosimetry. This could lead to an explosion in scientific production in this field. In the present paper the historical background behind the study of the internal pair production of the 0+/0+ transition of 90Zr is presented along with most up to date measured branch ratio values. An overview of most recent studies that exploit β+ particles emitted from 90Y for PET acquisitions is also provided.Atoms2013-03-0811Review10.3390/atoms10100022122218-20042013-03-08doi: 10.3390/atoms1010002Marco D'Arienzo<![CDATA[Atoms, Vol. 1, Pages 1: Welcome to Atoms: A New Open Access Journal]]>
http://www.mdpi.com/2218-2004/1/1/1
There is no doubt that it is an exciting time to be studying quantum properties of atoms, molecules, and nuclei. Increasingly deep connections between long-established fields: “atomic physics”, “molecular physics”, “chemical physics”, “nuclear physics”, “scattering theory”, “nuclear magnetic resonance”, “quantum optics”, etc., are blurring old research labels. Atoms is a new open access journal with a broad scope that will aim to capture some of these exciting changes and developments, with a quantum flavor. The Editorial Board's collective expertise spans the fields involved and reflects the international communities active in these areas. [...]Atoms2012-12-1711Editorial10.3390/atoms1010001112218-20042012-12-17doi: 10.3390/atoms1010001James Babb