Atoms
http://www.mdpi.com/journal/atoms
Latest open access articles published in Atoms at http://www.mdpi.com/journal/atoms<![CDATA[Atoms, Vol. 3, Pages 450-473: Cavity Quantum Electrodynamics of Continuously Monitored Bose-Condensed Atoms]]>
http://www.mdpi.com/2218-2004/3/3/450
We study cavity quantum electrodynamics of Bose-condensed atoms that are subjected to continuous monitoring of the light leaking out of the cavity. Due to a given detection record of each stochastic realization, individual runs spontaneously break the symmetry of the spatial profile of the atom cloud and this symmetry can be restored by considering ensemble averages over many realizations. We show that the cavity optomechanical excitations of the condensate can be engineered to target specific collective modes. This is achieved by exploiting the spatial structure and symmetries of the collective modes and light fields. The cavity fields can be utilized both for strong driving of the collective modes and for their measurement. In the weak excitation limit the condensate–cavity system may be employed as a sensitive phonon detector which operates by counting photons outside the cavity that have been selectively scattered by desired phonons.Atoms2015-09-2333Article10.3390/atoms30304504504732218-20042015-09-23doi: 10.3390/atoms3030450Mark LeeJanne Ruostekoski<![CDATA[Atoms, Vol. 3, Pages 433-449: A Realization of a Quasi-Random Walk for Atoms in Time-Dependent Optical Potentials]]>
http://www.mdpi.com/2218-2004/3/3/433
We consider the time dependent dynamics of an atom in a two-color pumped cavity, longitudinally through a side mirror and transversally via direct driving of the atomic dipole. The beating of the two driving frequencies leads to a time dependent effective optical potential that forces the atom into a non-trivial motion, strongly resembling a discrete random walk behavior between lattice sites. We provide both numerical and analytical analysis of such a quasi-random walk behavior.Atoms2015-09-2333Article10.3390/atoms30304334334492218-20042015-09-23doi: 10.3390/atoms3030433Torsten HinkelHelmut RitschClaudiu Genes<![CDATA[Atoms, Vol. 3, Pages 422-432: Quantum Entanglement and Shannon Information Entropy for the Doubly Excited Resonance State in Positronium Negative Ion]]>
http://www.mdpi.com/2218-2004/3/3/422
In the present work, we report an investigation on quantum entanglement in the doubly excited 2s2 1Se resonance state of the positronium negative ion by using highly correlated Hylleraas type wave functions, determined by calculation of the density of resonance states with the stabilization method. Once the resonance wave function is obtained, the spatial (electron-electron orbital) entanglement entropies (von Neumann and linear) can be quantified using the Schmidt decomposition method. Furthermore, Shannon entropy in position space, a measure for localization (or delocalization) for such a doubly excited state, is also calculated.Atoms2015-09-2133Article10.3390/atoms30304224224322218-20042015-09-21doi: 10.3390/atoms3030422Chien-Hao LinYew Ho<![CDATA[Atoms, Vol. 3, Pages 407-421: Extreme Ultraviolet Spectra of Few-Times Ionized Tungsten for Divertor Plasma Diagnostics]]>
http://www.mdpi.com/2218-2004/3/3/407
The extreme ultraviolet (EUV) emission from few-times ionized tungsten atoms has been experimentally studied at the Livermore electron beam ion trap facility. The ions were produced and confined during low-energy operations of the EBIT-I electron beam ion trap. By varying the electron-beam energy from around 30–300 eV, tungsten ions in charge states expected to be abundant in tokamak divertor plasmas were excited, and the resulting EUV emission was studied using a survey spectrometer covering 120–320 Å. It is found that the emission strongly depends on the excitation energy; below 150 eV, it is relatively simple, consisting of strong isolated lines from a few charge states, whereas at higher energies, it becomes very complex. For divertor plasmas with tungsten impurity ions, this emission should prove useful for diagnostics of tungsten flux rates and charge balance, as well as for radiative cooling of the divertor volume. Several lines in the 194–223 Å interval belonging to the spectra of five- and seven-times ionized tungsten (Tm-like W VI and Ho-like W VIII) were also measured using a high-resolution spectrometer.Atoms2015-09-0933Article10.3390/atoms30304074074212218-20042015-09-09doi: 10.3390/atoms3030407Joel ClementsonThomas LennartssonPeter Beiersdorfer<![CDATA[Atoms, Vol. 3, Pages 392-406: Probing and Manipulating Fermionic and Bosonic Quantum Gases with Quantum Light]]>
http://www.mdpi.com/2218-2004/3/3/392
We study the atom-light interaction in the fully quantum regime, with the focus on off-resonant light scattering into a cavity from ultracold atoms trapped in an optical lattice. The detection of photons allows the quantum nondemolition (QND) measurement of quantum correlations of the atomic ensemble, distinguishing between different quantum states. We analyse the entanglement between light and matter and show how it can be exploited for realising multimode macroscopic quantum superpositions, such as Schrödinger cat states, for both bosons and fermions. We provide examples utilising different measurement schemes and study their robustness to decoherence. Finally, we address the regime where the optical lattice potential is a quantum dynamical variable and is modified by the atomic state, leading to novel quantum phases and significantly altering the phase diagram of the atomic system.Atoms2015-09-0233Article10.3390/atoms30303923924062218-20042015-09-02doi: 10.3390/atoms3030392Thomas ElliottGabriel MazzucchiWojciech KozlowskiSantiago Caballero-Benitez Igor Mekhov<![CDATA[Atoms, Vol. 3, Pages 367-391: Experiments with Highly-Ionized Atoms in Unitary Penning Traps]]>
http://www.mdpi.com/2218-2004/3/3/367
Highly-ionized atoms with special properties have been proposed for interesting applications, including potential candidates for a new generation of optical atomic clocks at the one part in 1019 level of precision, quantum information processing and tests of fundamental theory. The proposed atomic systems are largely unexplored. Recent developments at NIST are described, including the isolation of highly-ionized atoms at low energy in unitary Penning traps and the use of these traps for the precise measurement of radiative decay lifetimes (demonstrated with a forbidden transition in Kr17+), as well as for studying electron capture processes.Atoms2015-08-1433Article10.3390/atoms30303673673912218-20042015-08-14doi: 10.3390/atoms3030367Shannon HoogerheideAung NaingJoan DreilingSamuel BrewerNicholas GuiseJoseph Tan<![CDATA[Atoms, Vol. 3, Pages 348-366: Cavity-Assisted Generation of Sustainable Macroscopic Entanglement of Ultracold Gases]]>
http://www.mdpi.com/2218-2004/3/3/348
Prospects for reaching persistent entanglement between two spatially-separated atomic Bose–Einstein condensates are outlined. The system setup comprises two condensates loaded in an optical lattice, which, in return, is confined within a high-Q optical resonator. The system is driven by an external laser that illuminates the atoms, such that photons can scatter into the cavity. In the superradiant phase, a cavity field is established, and we show that the emerging cavity-mediated interactions between the two condensates is capable of entangling them despite photon losses. This macroscopic atomic entanglement is sustained throughout the time-evolution apart from occasions of sudden deaths/births. Using an auxiliary photon mode and coupling it to a collective quadrature of the two condensates, we demonstrate that the auxiliary mode’s squeezing is proportional to the atomic entanglement, and as such, it can serve as a probe field of the macroscopic entanglement.Atoms2015-08-0433Article10.3390/atoms30303483483662218-20042015-08-04doi: 10.3390/atoms3030348Chaitanya JoshiJonas Larson<![CDATA[Atoms, Vol. 3, Pages 339-347: Influence of Virtual Photon Process on the Generation of Squeezed Light from Atoms in an Optical Cavity]]>
http://www.mdpi.com/2218-2004/3/3/339
We show that a collection of two-level atoms in an optical cavity beyond the rotating wave approximation and in the dispersive-adiabatic and non-dispersive adiabatic regime constitutes a nonlinear medium and is capable of generating squeezed state of light. It is found that squeezing produced in the non-dispersive adiabatic regime is significantly high compared to that produced in the dispersive-adiabatic limit. On the other hand, we also show that it could be possible to observe the Dicke superradiant quantum phase transition in the dispersive-adiabatic regime where the Ã2 term is negligible. Such a system can be an essential component of a larger quantum-communication system.Atoms2015-07-2433Article10.3390/atoms30303393393472218-20042015-07-24doi: 10.3390/atoms3030339Aranya Bhattacherjee<![CDATA[Atoms, Vol. 3, Pages 320-338: On the Classical Coupling between Gravity and Electromagnetism]]>
http://www.mdpi.com/2218-2004/3/3/320
Coupling between electromagnetism and gravity, manifested as the distorted Coulomb field of a charge distribution in a gravitational field, has never been observed. A physical system consisting of an electron in a charged shell provides a coupling that is orders of magnitude stronger than for any previously-considered system. A shell voltage of one megavolt is required to establish a gravitationally-induced electromagnetic force equal in magnitude to the force of gravity on an electron. The experimental feasibility of detecting these forces on an electron is discussed. The effect establishes a relation between Einstein’s energy-mass equivalence and the coupling between electromagnetism and gravity.Atoms2015-06-3033Article10.3390/atoms30303203203382218-20042015-06-30doi: 10.3390/atoms3030320Maria BeckerAdam CaprezHerman Batelaan<![CDATA[Atoms, Vol. 3, Pages 299-319: Detailed Analysis of Configuration Interaction and Calculation of Radiative Transition Rates in Seven Times Ionized Tungsten (W VIII)]]>
http://www.mdpi.com/2218-2004/3/3/299
A new set of oscillator strengths and transition probabilities for EUV spectral lines of seven times ionized tungsten (W VIII) is reported in the present paper. These results have been obtained using the pseudo-relativistic Hartree-Fock (HFR) method combined with a semi-empirical optimization of the radial parameters minimizing the discrepancies between computed energy levels and available experimental data. The final physical model considered in the calculations has been chosen further to a detailed investigation of the configuration interaction in this atomic system characterized by complex configurations of the type 4f145s25p5, 4f145s25p4nl, 4f145s5p6, 4f135s25p6, 4f135s25p5nl and 4f125s25p6nl (nl = 5d, 6s).Atoms2015-06-3033Article10.3390/atoms30302992993192218-20042015-06-30doi: 10.3390/atoms3030299Jérôme DeprincePascal Quinet<![CDATA[Atoms, Vol. 3, Pages 273-298: Spectra of W VIII and W IX in the EUV Region]]>
http://www.mdpi.com/2218-2004/3/3/273
The results obtained on the W VIII spectrum as well as on the isoelectronic spectra Lu V, Hf VI, Ta VII, and Re IX in the VUV wavelength region are summarized with emphasis on the main trends along the isoelectronic sequence. A total of 187 lines of W VIII in the region of 160–271 Å were accurately measured and identified, 98 levels were found, and transition probabilities calculated. The isoelectronic regularities support the data on W VIII. A list of spectral lines in the region of 170–199 Å, considered as belonging to W IX, is presented.Atoms2015-06-3033Article10.3390/atoms30302732732982218-20042015-06-30doi: 10.3390/atoms3030273Alexander RyabtsevEdward KononovRimma KildiyarovaWan-Ü Tchang-BrilletJean-Francois WyartNorbert ChampionChristophe Blaess<![CDATA[Atoms, Vol. 3, Pages 260-272: Tungsten Data for Current and Future Uses in Fusion and Plasma Science]]>
http://www.mdpi.com/2218-2004/3/2/260
We give a brief overview of our recent experimental and theoretical work involving highly charged tungsten ions in high-temperature magnetically confined plasmas. Our work includes X-ray and extreme ultraviolet spectroscopy, state-of-the-art structure calculations, the generation of dielectronic recombination rate coefficients, collisional-radiative spectral modeling and assessments of the atomic data need for X-ray diagnostics monitoring of the parameters of the core plasma of future tokamaks, such as ITER. We give examples of our recent results in these areas.Atoms2015-06-1532Article10.3390/atoms30202602602722218-20042015-06-15doi: 10.3390/atoms3020260Peter BeiersdorferJoel ClementsonUlyana Safronova<![CDATA[Atoms, Vol. 3, Pages 195-259: MCDHF Calculations and Beam-Foil EUV Spectra of Boron-Like Sodium Ions (Na VII)]]>
http://www.mdpi.com/2218-2004/3/2/195
Atomic data, such as wavelengths and line identifications, are necessary for many applications, especially in plasma diagnostics and for interpreting the spectra of distant astrophysical objects. The number of valence shell electrons increases the complexity of the computational problem. We have selected a five-electron ion, Na6+ (with the boron-like spectrum Na VII), for looking into the interplay of measurement and calculation. We summarize the available experimental work, perform our own extensive relativistic configuration interaction (RCI) computations based on multi-configuration Dirac–Hartree–Fock (MCDHF) wave functions, and compare the results to what is known of the level structure. We then discuss problems with databases that have begun to combine observations and computations.Atoms2015-06-0932Article10.3390/atoms30201951952592218-20042015-06-09doi: 10.3390/atoms3020195Per JönssonJörgen EkmanElmar Träbert<![CDATA[Atoms, Vol. 3, Pages 182-194: Photon-Induced Spin-Orbit Coupling in Ultracold Atoms inside Optical Cavity]]>
http://www.mdpi.com/2218-2004/3/2/182
We consider an atom inside a ring cavity, where a plane-wave cavity field together with an external coherent laser beam induces a two-photon Raman transition between two hyperfine ground states of the atom. This cavity-assisted Raman transition induces effective coupling between atom’s internal degrees of freedom and its center-of-mass motion. In the meantime, atomic dynamics exerts a back-action to cavity photons. We investigate the properties of this system by adopting a mean-field and a full quantum approach, and show that the interplay between the atomic dynamics and the cavity field gives rise to intriguing nonlinear phenomena.Atoms2015-05-2632Article10.3390/atoms30201821821942218-20042015-05-26doi: 10.3390/atoms3020182Lin DongChuanzhou ZhuHan Pu<![CDATA[Atoms, Vol. 3, Pages 162-181: Tungsten Ions in Plasmas: Statistical Theory of Radiative-Collisional Processes]]>
http://www.mdpi.com/2218-2004/3/2/162
The statistical model for calculations of the collisional-radiative processes in plasmas with tungsten impurity was developed. The electron structure of tungsten multielectron ions is considered in terms of both the Thomas-Fermi model and the Brandt-Lundquist model of collective oscillations of atomic electron density. The excitation or ionization of atomic electrons by plasma electron impacts are represented as photo-processes under the action of flux of equivalent photons introduced by E. Fermi. The total electron impact single ionization cross-sections of ions Wk+ with respective rates have been calculated and compared with the available experimental and modeling data (e.g., CADW). Plasma radiative losses on tungsten impurity were also calculated in a wide range of electron temperatures 1 eV–20 keV. The numerical code TFATOM was developed for calculations of radiative-collisional processes involving tungsten ions. The needed computational resources for TFATOM code are orders of magnitudes less than for the other conventional numerical codes. The transition from corona to Boltzmann limit was investigated in detail. The results of statistical approach have been tested by comparison with the vast experimental and conventional code data for a set of ions Wk+. It is shown that the universal statistical model accuracy for the ionization cross-sections and radiation losses is within the data scattering of significantly more complex quantum numerical codes, using different approximations for the calculation of atomic structure and the electronic cross-sections.Atoms2015-05-2532Article10.3390/atoms30201621621812218-20042015-05-25doi: 10.3390/atoms3020162Alexander DemuraMikhail KadomtsevValery LisitsaVladimir Shurygin<![CDATA[Atoms, Vol. 3, Pages 120-161: Fusion-Related Ionization and Recombination Data for Tungsten Ions in Low to Moderately High Charge States]]>
http://www.mdpi.com/2218-2004/3/2/120
Collisional processes and details of atomic structure of heavy many-electron atoms and ions are not yet understood in a fully satisfying manner. Experimental studies are required for guiding new theoretical approaches. In response to fusion-related needs for collisional and spectroscopic data on tungsten atoms in all charge states, a project has been initiated in which electron-impact and photon-induced ionization as well as photorecombination of Wq+ ions are studied. Cross sections and rate coefficients were determined for charge states q ranging from q = 1 to q = 5 for photoionization, for q = 1 up to q = 19 for electron-impact ionization and for q = 18 to q = 21 for electron-ion recombination. An overview, together with a critical assessment of the methods and results is provided.Atoms2015-05-2032Article10.3390/atoms30201201201612218-20042015-05-20doi: 10.3390/atoms3020120Alfred Müller<![CDATA[Atoms, Vol. 3, Pages 86-119: Radiative Recombination and Photoionization Data for Tungsten Ions. Electron Structure of Ions in Plasmas]]>
http://www.mdpi.com/2218-2004/3/2/86
Theoretical studies of tungsten ions in plasmas are presented. New calculations of the radiative recombination and photoionization cross-sections, as well as radiative recombination and radiated power loss rate coefficients have been performed for 54 tungsten ions for the range W6+–W71+. The data are of importance for fusion investigations at the reactor ITER, as well as devices ASDEX Upgrade and EBIT. Calculations are fully relativistic. Electron wave functions are found by the Dirac–Fock method with proper consideration of the electron exchange. All significant multipoles of the radiative field are taken into account. The radiative recombination rates and the radiated power loss rates are determined provided the continuum electron velocity is described by the relativistic Maxwell–Jüttner distribution. The impact of the core electron polarization on the radiative recombination cross-section is estimated for the Ne-like iron ion and for highly-charged tungsten ions within an analytical approximation using the Dirac–Fock electron wave functions. The effect is shown to enhance the radiative recombination cross-sections by ≲20%. The enhancement depends on the photon energy, the principal quantum number of polarized shells and the ion charge. The influence of plasma temperature and density on the electron structure of ions in local thermodynamic equilibrium plasmas is investigated. Results for the iron and uranium ions in dense plasmas are in good agreement with previous calculations. New calculations were performed for the tungsten ion in dense plasmas on the basis of the average-atom model, as well as for the impurity tungsten ion in fusion plasmas using the non-linear self-consistent field screening model. The temperature and density dependence of the ion charge, level energies and populations are considered.Atoms2015-05-1832Article10.3390/atoms3020086861192218-20042015-05-18doi: 10.3390/atoms3020086Malvina TrzhaskovskayaVladimir Nikulin<![CDATA[Atoms, Vol. 3, Pages 76-85: Collisional-Radiative Modeling of Tungsten at Temperatures of 1200–2400 eV]]>
http://www.mdpi.com/2218-2004/3/2/76
We discuss new collisional-radiative modeling calculations of tungsten at moderate temperatures of 1200 to 2400 eV. Such plasma conditions are relevant to ongoing experimental work at ASDEX Upgrade and are expected to be relevant for ITER. Our calculations are made using the Los Alamos National Laboratory (LANL) collisional-radiative modeling ATOMIC code. These calculations formed part of a submission to the recent NLTE-8 workshop that was held in November 2013. This series of workshops provides a forum for detailed comparison of plasma and spectral quantities from NLTE collisional-radiative modeling codes. We focus on the LANL ATOMIC calculations for tungsten that were submitted to the NLTE-8 workshop and discuss different models that were constructed to predict the tungsten emission. In particular, we discuss comparisons between semi-relativistic configuration-average and fully relativistic configuration-average calculations. We also present semi-relativistic calculations that include fine-structure detail, and discuss the difficult problem of ensuring completeness with respect to the number of configurations included in a CR calculation.Atoms2015-04-3032Article10.3390/atoms302007676852218-20042015-04-30doi: 10.3390/atoms3020076James ColganChristopher FontesHonglin ZhangJoseph Abdallah<![CDATA[Atoms, Vol. 3, Pages 53-75: Fully Relativistic Electron Impact Excitation Cross-Section and Polarization for Tungsten Ions]]>
http://www.mdpi.com/2218-2004/3/2/53
Electron impact excitation of highly charged tungsten ions in the framework of a fully relativistic distorted wave approach is considered in this paper. Calculations of electron impact excitation cross-sections for the M- and L-shell transitions in the tungsten ions Wn+ (n = 44–66) and polarization of the decay of photons from the excited tungsten ions are briefly reviewed and discussed. New calculations in the wide range of incident electron energies are presented for M-shell transitions in the K-like through Ne-like tungsten ions.Atoms2015-04-2832Article10.3390/atoms302005353752218-20042015-04-28doi: 10.3390/atoms3020053 Priti DiptiLalita SharmaRajesh Srivastava<![CDATA[Atoms, Vol. 3, Pages 2-52: Ab-Initio Calculations of Level Energies, Oscillator Strengths and Radiative Rates for E1 Transitions in Beryllium-Like Iron]]>
http://www.mdpi.com/2218-2004/3/1/2
In the present work, energy levels, oscillator strengths, radiative rates and wavelengths of Be-like iron (Fe\(^{22+}\)) from ab-initio calculations using the multiconfiguration Dirac-Hartree-Fock method are presented. These quantities have been calculated for a set of configurations in the general form \(1s^2\,nl\,n'l'\) where \(n=2,3\) and \(\,n'=2,3,4,5\) and \(l=s,p,d\) and \(\,l'=s, p, d, f, g\). In addition, excitations of up to four electrons, including core-electron excitations, have been considered to improve the quality of the wave functions. This study comprises an extensive set of E1 transition rates between states with different \(J\). The present results are compared with the available experimental and theoretical data.Atoms2015-01-2031Article10.3390/atoms30100022522218-20042015-01-20doi: 10.3390/atoms3010002Ahmed El-MaarefStefan SchippersAlfred Müller<![CDATA[Atoms, Vol. 3, Pages 1: Acknowledgement to Reviewers of Atoms in 2014]]>
http://www.mdpi.com/2218-2004/3/1/1
The editors of Atoms would like to express their sincere gratitude to the following reviewers for assessing manuscripts in 2014:[...]Atoms2015-01-0931Editorial10.3390/atoms3010001112218-20042015-01-09doi: 10.3390/atoms3010001 Atoms Editorial Office<![CDATA[Atoms, Vol. 2, Pages 382-390: Estimating Relative Uncertainty of Radiative Transition Rates]]>
http://www.mdpi.com/2218-2004/2/4/382
We consider a method to estimate relative uncertainties of radiative transition rates in an atomic spectrum. Few of these many transitions have had their rates determined by more than two reference-quality sources. One could estimate uncertainties for each transition, but analyses with only one degree of freedom are generally fraught with difficulties. We pursue a way to empirically combine the limited uncertainty information in each of the many transitions. We “pool” a dimensionless measure of relative dispersion, the “Coefficient of Variation of the mean,” \(C_{V}^{n} \equiv s/(\bar{x}\sqrt{n})\). Here, for each transition rate, “s” is the standard deviation, and “\(\bar{x}\)” is the mean of “n” independent data sources. \(C_{V}^{n}\) is bounded by zero and one whenever the determined quantity is intrinsically positive.) We scatter-plot the \(C_{V}^{n} \)as a function of the “line strength” (here a more useful radiative transition rate than transition probability). We find a curve through comparable \(C_{V}^{n} \)as that envelops a specified percentage of the \(C_{V}^{n} \)s (e.g. 95%). We take this curve to represent the expanded relative uncertainty of the mean. The method is most advantageous when the number of determined transition rates is large while the number of independent determinations per transition is small. The transition rate data of Na III serves as an example.Atoms2014-11-2524Article10.3390/atoms20403823823902218-20042014-11-25doi: 10.3390/atoms2040382Daniel Kelleher<![CDATA[Atoms, Vol. 2, Pages 378-381: Special Issue on Spectral Line Shapes in Plasmas]]>
http://www.mdpi.com/2218-2004/2/3/378
Line-shape analysis is one of the most important tools for diagnostics of both laboratory and space plasmas. Its reliable implementation requires sufficiently accurate calculations, which imply the use of analytic methods and computer codes of varying complexity, and, necessarily, varying limits of applicability and accuracy. However, studies comparing different computational and analytic methods are almost non-existent. The Spectral Line Shapes in Plasma (SLSP) code comparison workshop series [1] was established to fill this gap. Numerous computational cases considered in the two workshops organized to date (in April 2012 and August 2013 in Vienna, Austria) not only serve the purpose of code comparison, but also have applications in research of magnetic fusion, astrophysical, laser-produced plasmas, and so on. Therefore, although the first workshop was briefly reviewed elsewhere [2], and will likely be followed by a review of the second one, it was unanimously decided by the participants that a volume devoted to results of the workshops was desired. It is the main purpose of this special issue.Atoms2014-08-0723Editorial10.3390/atoms20303783783812218-20042014-08-07doi: 10.3390/atoms2030378Evgeny StambulchikAnnette CalistiHyun-Kyung ChungManuel González<![CDATA[Atoms, Vol. 2, Pages 357-377: On the Application of Stark Broadening Data Determined with a Semiclassical Perturbation Approach]]>
http://www.mdpi.com/2218-2004/2/3/357
The significance of Stark broadening data for problems in astrophysics, physics, as well as for technological plasmas is discussed and applications of Stark broadening parameters calculated using a semiclassical perturbation method are analyzed.Atoms2014-08-0723Article10.3390/atoms20303573573772218-20042014-08-07doi: 10.3390/atoms2030357Milan DimitrijevićSylvie Sahal-Bréchot<![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