Transition Array Research Articles

Stark broadening of Cu II spectral lines

Electron-impact (Stark) full widths at half intensity maximum for 22 spectral lines of singly charged copper ion (Cu II) have been calculated by employing the modified semiempirical method. The calculations have been performed for an electron density of 1017 cm−3 and for a temperature range from 5 000 K up to 80 000 K. The obtained results, have been used to demonstrate similarities and regularities of Stark widths of Cu II spectral lines within a multiplet, a supermultiplet and a transition array. The obtained results have also been compared with the results of experiments and other theoretical data.

Collisional-Radiative modeling of unresolved transition array spectra near 200 Å from W17+-W25+ emissions for diagnostics of ITER edge plasma

Tungsten (W) is one of the major impurities in ITER and future DEMO reactors. However,diagnosing the ion density, temperature, and spatial distribution of tungsten ions in intermediate charge states, such as W8+-W27+, is difficult because of the lack of spectral line data. In this study, we observed a tungsten Unresolved Transition Array (UTA) spectrum, which has a pseudo-continuum structure, around W20+ in the Extreme Ultraviolet wavelength region in the Large Helical Device (LHD). We conducted Collisional-Radiative (CR) modeling for W17+-W25+. Two pseudo-continuum peaks corresponding to 5 s-5p transition and transition between doubly excited states of 5 s2-5s5p, are strongly emitted around 200 Å for each ion. The synthesized spectrum of W17+-W25+ ions reproduced the observed LHD spectrum near 200 Å. From the electron temperature dependence of the UTA spectral shape, the UTA shifted toward longer wavelength region with several pseudo-continuum peaks appearing for ions in lower charge states, with decreasing electron temperature from 0.4 keV to 0.2 keV. This result qualitatively explained the observed time evolution of the spectrum.

Spectroscopic analysis of tungsten spectra in extreme-ultraviolet range of 10-480 Å observed from EAST tokamak with full tungsten divertor

Tungsten spectra in extreme ultraviolet (EUV) wavelength range of 10-480 Å have been observed from high-temperature plasmas in Experimental Advanced Superconducting Tokamak (EAST) with full tungsten divertor using four fast-time-response EUV spectrometers of EUV_Short (5-45 Å), EUV_Long_a (40–180 Å), EUV_Long_c (130–330 Å) and EUV_Long_b (270–480 Å) and two space-resolved EUV spectrometers of EUV_Short2_d (45–70 Å) and EUV_Long2_d (40–130 Å). The wavelength of measured spectra is accurately calibrated based on several well-known spectral lines emitted from low-Z (He, Li, C, N and O), medium-Z (Fe and Cu) and high-Z (Mo) impurity ions. Measurements of the tungsten spectra were taken from discharges accompanied with a transient tungsten burst event, which creates a pulsed influx of tungsten atoms into the EAST plasma. The tungsten spectra observed before and after the burst event are carefully analyzed with temporal behavior and radial profile distribution of the tungsten line intensity. As a result, 213 tungsten lines are successfully confirmed in the spectra observed after the tungsten burst, and the results are summarized in tables. These tungsten lines include line identifications of 78 lines of W XXIII - W XLVI (W22+ - W45+) at 10–140 Å and 88 lines of W V - W IX (W4+ - W8+) at 160–480 Å, while 47 tungsten lines at 50–380 Å could not be clarified the transition. In addition, quasi-continuum spectra called unresolved transition array (UTA) from tungsten ions in low- and high-ionization stages are also analyzed in three wavelength ranges of 18–38 Å, 45–70 Å and 150–280 Å at which W XXIII - W XXXVIII (W22+ - W37+), W XXVII - W XLVI (W26+ - W45+) and W VI—W IX (W5+ - W8+) are dominantly emitted, respectively. Through the analysis it is found that charge state distributions of tungsten UTA at 140–220 Å significantly vary with decrease in the electron temperature. Ionization stages of all observed tungsten lines including both isolated and quasi-continuum lines are experimentally reconfirmed by comparing the radial intensity profile with the electron temperature profile. Finally, spectral lines useful for tungsten diagnostic in fusion plasmas are selected and marked in the tables.

Shock-Layer Measurements in T5 Shock Tunnel Hypersonic Flows Around a Cylinder Model

We report on near-body measurements of temperature and nitric oxide (NO) concentration in the hypersonic flows around a cylindrical test article in the Caltech T5 reflected shock tunnel. Flow measurements were made at 50 kHz using tunable diode laser absorption spectroscopy, deploying six lasers to probe an array of quantum state-specific transitions. Laser beams were positioned both in the freestream and behind the bow shock at specific locations deemed pertinent to computational fluid dynamics comparison and kinetic model evaluation. The fractions of laser beam pathlengths behind the shock in different spatial regions were also discerned, thus providing a measurement of shock location. This study consists of six total experiments (“shots”) across two Mach ∼5 conditions, characterized by total enthalpies of 8 and 16 MJ/kg and freestream velocities of 3.5 and 5 km/s, respectively. Freestream measurements generally concur with prior works in the T5, but with some non-trivial differences. Shock-layer measurements span from 2000 to 6000 K and feature noteworthy and expected variety among different zones within the post-shock region. Thermal equilibrium is generally held throughout the flowfield, but chemical nonequilibrium is commonly observed. NO is the primary spectroscopic target, but measurements of carbon monoxide, carbon dioxide, water, and atomic oxygen provide supplementary insights.

Analysis of the extreme ultraviolet broadband spectral characteristics and spatiotemporal evolution of laser-produced germanium plasmas

This paper presents comprehensive spectral measurements and a theoretical analysis of laser-produced germanium (Ge) plasma within the 7.5–17 nm wavelength range, with the measurements being performed using spatiotemporally-resolved emission spectroscopy. We obtained and analyzed the extreme ultraviolet (EUV) spectra and their variations meticulously at various positions adjacent to the target surface. The 3p and 3d excitations of Ge ions spanning from Ge4+ to Ge13+ were calculated using the Cowan configuration interaction codes, with particular emphasis being placed on analysis of the spectral line distributions in the 3d-np, 3d-nf, and 3p-3d, 4s, 4d transition arrays. This analysis indicated the contributions made by these transition arrays to the broadband spectral features that were observed experimentally. By using a steady-state collisional radiation model along with a normalized Boltzmann distribution assumption, we clarified the predominant contributions of the 3d-4p and 3p-3d transitions from the Ge7+ to Ge9+ ions in close proximity to the target surface, along with those from the Ge5+ and Ge6+ ions at greater distances. Furthermore, by combining the results above with a plasma dynamics evolution analysis, we gained insights into how the plasma's transient and nonuniform properties influence the analysis of complex EUV band spectral profiles and examine their implications for spectral diagnostics. These results will be useful for plasma spectral diagnosis and for application to development of pulsed short-wavelength light sources.

Transition probabilities and suitable coupling scheme for 6p→6s transition array of neutral xenon using hollow cathode discharge lamp technique

In the present work, analyses have been performed to determine spectroscopic parameters, including transition probabilities, and relative line strengths of discharge-produced xenon plasma. We present the transition probabilities of twenty-three emission lines originating from the 5p56p →5p56s transition array of neutral xenon covering the wavelength range from 450 to 1100 nm using a xenon-filled hollow cathode discharge lamp. The experimental absolute transition probabilities have been measured by combining the reported lifetimes of upper levels with the integrated spectral intensities of xenon transitions. The results agree well with the reported data in the NIST database, where available. The theoretical line strengths for all spectral transitions originating from the 5p56p→5p56s transition array have been calculated in the LS, LK, jj, and jck coupling schemes using the 3j, 6j, and 9j symbol relations. Furthermore, the normalized experimental line strengths have also been measured and compared with theoretical line strengths, which confirm that the jj and jck coupling scheme is more appropriate for the level designation of xenon.

Stark broadening of Pd II spectral lines

Stark widths for 47 spectral lines of singly charged palladium ion (Pd II) have been calculated with the help of the modified semiempirical method. The calculations have been performed for an electron density of 1017 cm−3 and for a temperature range from 5 000 K up to 80 000 K. Employing the obtained results, we investigated the influence of Stark broadening in Pd II spectra of DB and DO white dwarfs as well as A type stars. Moreover, similarities and regularities of Stark widths of Pd II spectral lines within a multiplet, a supermultiplet and a transition array have been discussed.

The Temperature and Density of a Solar Flare Kernel Measured from Extreme-ultraviolet Lines of O iv

Previously unexplored diagnostics of O iv in the extreme-ultraviolet region 260–280 Å are used to derive a temperature and density for a solar flare kernel observed on 2012 March 9 with the Extreme-ultraviolet Imaging Spectrometer on the Hinode satellite. Seven lines from the 2s2p 2–2s2p3s transition array between 271.99 and 272.31 Å are both temperature- and density-sensitive relative to the line at 279.93 Å. The temperature, T, is constrained with the λ268.02/λ279.93 ratio, giving a value of log(T/K)=5.10±0.03 . The ratio λ272.13/λ279.93 then yields an electron number density, N e, of log(Ne/cm−3)=12.52 with a lower limit of 11.90 and an upper limit of 14.40. The O iv emitting volume is estimated to be 0.″4 (300 km) across. Additional O iv lines at 196, 207, and 260 Å are consistent with the derived temperature and density but have larger uncertainties from the radiometric calibration and blending. Density diagnostics of O v and Mg vii from the same spectrum are consistent with a constant pressure of 1017.0 K cm−3 through the transition region. The temperature derived from O iv supports recent results that O iv is formed around 0.10 dex lower at high densities compared to standard zero-density ionization balance calculations.

The Thomas-Kuhn-Reiche sum rule for bound electrons of ions in warm dense plasmas

The Thomas-Kuhn-Reiche oscillator strength sum rule is analyzed for the case of ionized atoms in warm dense plasmas: The statistical summation of the bound-bound and the bound-free oscillator strength is proportional to the average bound electrons. This sum rule is checked for approximated absorption spectra like the detailed line accounting, detailed configurations accounting, the super transition arrays and the average atom using the CRSTA code. We show that the sum rule is properly satisfied for various elements in ranges of temperature-density that have sufficient bound orbitals. On the other hand, for the cases of few bound orbitals, the sum-rule is poorly satisfied, like in the case of high density and low temperature.

L-Mn dielectronic recombination of cerium ions in a room-temperature EBIT

We explore the dielectronic recombination structures at the electron beam ion trap at Jagiellonian University in Cracow, emited by cerium that is produced by the high-current cathode made of iridium and cerium. Small amounts of these elements evaporate from the cathode and form low-intensity admixtures within the electron-ion plasma in the EBIT. Their presence and specific ionic population can be observed by examining the spectral characteristics resulting from the DR process. Results have been compared with flexible atomic code calculations, working in unresolved transition array mode, providing identification of the charge states. Here we show that this mode provides quick calculations of very complex data with enough reliability for experimental comparison. These observations highlight which DR features and corresponding charge states that should be present in spectra obtained in EBITs with similar cathode specifications.

Statistical RTA simulations of atomic data for astrophysical opacity modeling in the context of kilonova emission

When considering some complex lanthanide ions characterized by a half-filled 4f subshell, the atomic structure Hamiltonian matrix sizes are so large that their diagonalization is challenging and therefore the atomic data of these ions are only used to compute the expansion opacity of a kilonova with difficulty. To avoid this problem, we propose a statistical simulation method to compute kilonova expansion opacities based on the resolved transition array (RTA) method of Bauche et al (1991 Phys. Rev. A 44 5707). The atomic structure relativistic Hartree–Fock (HFR) method has been employed to compute the radial integrals necessary for our statistical RTA simulations where the atomic data are randomly drawn using their corresponding statistical distributions and to determine the exact expansion opacities where the atomic data are obtained by the diagonalization of the Hamiltonian matrix. The statistical RTA simulations carried out for two specific ions, i.e. Sm VIII and Eu VI, for which it is still possible to diagonalize the Hamiltonian matrix, reproduce well the expansion opacities computed using HFR atomic data. Based on this good agreements, the statistical RTA method was used to compute the expansion opacity of Dy VIII, which is determined through diagonalization with difficulty. The proposed statistical RTA simulation method allows the computation of reliable astrophysical expansion opacities which are of paramount importance for kilonova light curve modeling and spectral analysis.

Effect of multiply excited states to the EUV emission from yttrium-like tin

The spectral emission rate of yttrium-like tin (Sn11+) is investigated as the typical ion, which has a strong emission of extreme ultra-violet (EUV) light near the wavelength of 13.5 nm. The energy level structure of the tin ion is investigated using the non-relativesitic configuration average model to calculate the population in the local thermodynamic equilibrium, and the spectral structure of the unresolved transition array that has EUV emission is investigated based on the calculated atomic data using the HULLAC code. It is shown that the broad main peak is accompanied by the tail structure for shorter and longer wavelengths, which arises from multiply and inner-shell excited levels. The emission channels that significantly contribute to the spectrum are determined from a convergence analysis. The excited states below the ionization limit with a large population are shown to have a significant contribution to the emission.

The STAG code: A fully relativistic super transition array calculation using Green’s functions

Calculating opacities for a wide range of plasma conditions (i.e. temperature, density, element) requires detailed knowledge of the plasma configuration space and electronic structure. For plasmas composed of heavier elements, relativistic effects are important in both the electronic structure and the details of opacity spectra. We extend our previously described superconfiguration and super transition array capabilities (Gill et al., 2023) to include a fully relativistic formalism. The use of hybrid bound-continuum supershells in our superconfigurations demonstrates the importance of a consistent treatment of bound and continuum electrons in dense plasma opacities, and we expand the discussion of these consequences to include issues associated with equation of state and electron correlations between bound and continuum electrons.

Spatiotemporal mapping of nanotopography and thickness transitions of ultrathin foam films.

Freshly formed soap films, soap bubbles, or foam films display iridescent colors due to thin film interference that changes as squeeze flow drives drainage and a progressive decrease in film thickness. Ultrathin (thickness <100 nm) freestanding films of soft matter containing micelles, particles, polyelectrolyte-surfactant complexes, or other supramolecular structures or liquid crystalline phases display drainage via stratification. A fascinating array of thickness variations and transitions, including stepwise thinning and coexistence of thick-thin flat regions, arise in micellar foam films that undergo drainage via stratification. In this tutorial, we describe the IDIOM (interferometry digital imaging optical microscopy) protocols that combine the conventional interferometry principle with digital filtration and image analysis to obtain nanometer accuracy for thickness determination while having high spatial and temporal resolution. We provide fully executable image analysis codes and algorithms for the analysis of nanotopography and summarize some of the unique insights obtained for stratified micellar foam films.

Simulation of extreme ultraviolet radiation of laser induced discharge plasma

Extreme ultraviolet (EUV) light source is an important part of EUV lithography system in semiconductor manufacturing. The EUV light source requires that the 4p&lt;sup&gt;6&lt;/sup&gt;4d&lt;sup&gt;&lt;i&gt;n&lt;/i&gt;&lt;/sup&gt;-4p&lt;sup&gt;5&lt;/sup&gt;4d&lt;sup&gt;&lt;i&gt;n&lt;/i&gt;+1&lt;/sup&gt; + 4d&lt;sup&gt;&lt;i&gt;n&lt;/i&gt;-1&lt;/sup&gt;4f transitions of Sn&lt;sup&gt;8+~13+&lt;/sup&gt; ions emit thousands of lines which form unresolved transition arrays near 13.5 nm. Laser-induced discharge plasma is one of the important technical means to excite target into an appropriate plasma condition. Laser-induced discharge plasma has a simple structure and a low cost. It also has important applications in mask inspection, microscopic imaging, and spectral metrology. In the design and production process, there are many factors that can influence the conversion efficiency, such as current, electrode shape, and laser power density. The simulation method is a convenient way to provide guidance for optimizing the parameters. In this paper, a completed radiation magneto-hydrodynamic model is used to explore the dynamic characteristics of laser-induced discharge plasma and its EUV radiation characteristics. To improve the accuracy, a more detailed global equation of state model, an atomic structure calculation model including relativistic effect and a collision radiation model are proposed simultaneously. The simulation reconstructs the discharge process effectively, which is divided into five stages in the first half cycle of current, including expansion of laser plasma, column formation of discharge plasma, diffusion of discharge plasma, contraction of discharge plasma, and re-diffusion of discharge plasma. It is revealed that the pinch effect during the current rising time exerts a significant influence on the generation of EUV radiation. The conversion efficiency of EUV radiation is still low under our existing conditions, and hopefully a higher rising rate of current can improve the conversion efficiency in the future work.

Intersecting transitions among 2S/LGBTQ+ youth experiencing homelessness: A scoping review

BackgroundTwo-Spirit, lesbian, gay, bisexual, transgender, queer, and other sexual and gender minority (2S/LGBTQ+) youth under 30 years of age are inequitably impacted by homelessness. Root drivers of homelessness among 2S/LGBTQ+ youth and the service-related needs of this group are multifaceted and complex. A synthesis of research can inform responsive action to support 2S/LGBTQ+ youth experiencing and at risk for homelessness with the goal of promoting better health and material living conditions. ObjectiveTo summarize the literature addressing health and social transitions among homeless 2S/LGBTQ+ youth. MethodsThis scoping review study utilized PRISMA-ScR guidelines to search seven bibliographic databases for peer-reviewed, English-language empirical works published between 2000 and 2022. The sampling frame centered homeless 2S/LGBTQ+ youth, with attention to life-course transitions. Retrieved citations were de-duplicated and assessed for inclusion through title/abstract and full-text screening completed independently by two reviewers. Data were charted and synthesized with a descriptive summary and qualitative content analysis. ResultsThis scoping review yielded a total of 27 articles. Most articles reported on qualitative studies (n = 21) and originated from the United States (n = 18) and Canada (n = 6). Findings from the qualitative content analysis reflect intersecting health and social transitions related to: (i) leaving home, (ii) navigating street life, and (iii) orienting toward the future. The included studies detail the complex array of transitions 2S/LGBTQ+ youth navigate in relation to homelessness, often with limited supports and in structural contexts involving socioeconomic precarity. ConclusionsFindings underscore that multipronged and context-informed responses are required to meaningfully support 2S/LGBTQ+ youth experiencing and at risk for homelessness. Policy and practice interventions that are youth-centered, strengths-based, and grounded in a socioecological perspective may be optimally positioned to address the intersecting forms of structural vulnerability shaping transitions into and through homelessness for 2S/LGBTQ+ youth.

Review of Rydberg Spectral Line Formation in Plasmas

The present review is dedicated to the problem of an array of transitions between highly-excited atomic levels. Hydrogen atoms and hydrogen-like ions in plasmas are considered here. The presented methods focus on calculation of spectral line shapes. Fast and simple methods of universal ionic profile calculation for the Hnα (Δn=1) and Hnβ (Δn=2) spectral lines are demonstrated. The universal dipole matrix elements formulas for the Hnα and Hnβ transitions are presented. A fast method for spectral line shape calculations in the presence of an external magnetic field using the formulas for universal dipole matrix elements is proposed. This approach accounts for the Doppler and Stark–Zeeman broadening mechanisms. Ion dynamics effects are treated via the frequency fluctuation model. The accuracy of the presented model is discussed. A comparison of this approach with experimental data and the results of molecular dynamics simulation is demonstrated. The kinetics equation for the populations of highly-excited ionic states is solved in the parabolic representation. The population source associated with dielectronic recombination is considered.

Collisional-radiative modeling and radiative emission of tungsten in tokamak plasmas in the temperature range (800–5000) eV

We present new collisional-modeling calculations of tungsten plasmas at electron density of about 5 × 1013 cm−3 and for electron temperatures in the range 0.8–5 keV. These conditions are relevant to current tokamaks. In this temperature range, the modeling of the ionization balance and of spectra is a long-standing problem. Addressing this problem is also useful for plasmas that will be produced in the future tokamak ITER. In particular, we discuss the problem of ensuring completeness of the list of configurations included in the calculations. We also discuss comparisons of experimental measurements in the EUV range performed in the WEST tokamak with synthetized spectra based on the use of the unresolved transition array and of the spin–orbit split array formalisms. While this work does not rely on a precise identification of detailed lines, modeled spectra display emission features that looks quite similar to the experimental spectra. A conclusion is that standard calculation methods used for the evaluation of the configuration average collisional and radiative rates, are fine provided that a convenient list of configurations is used in the calculations.

Study of the 6.x nm short wavelength radiation spectra of laser-produced erbium plasmas for BEUV lithography

Beyond extreme ultraviolet (BEUV) radiation with a wavelength of 6.x nm for lithography is responsible for reducing the source wavelength to enable continued miniaturization of semiconductor devices. In this work, the Required BEUV light at 6.x nm wavelength was generated in dense and hot Nd:YAG laser-produced Er plasmas. The spectral contributions from the 4p–4d and 4d–4f transitions of singly, doubly and triply excited states of Er XXIV–Er XXXII in the BEUV band were calculated using Cowan and the Flexible Atomic Code. It was also found that the radiative transitions between multiply excited states dominate the narrow wavelength window around 6.x nm. Under the assumption of collisional radiative equilibrium of the laser-produced Er plasmas, the relative ion abundance in the experiment was inferred. Using the Boltzmann quantum state energy level distribution and Gram–Charlier fitting function of unresolved transition arrays (UTAs), the synthetic spectrum around 6.x nm was finally obtained and compared with the experimental spectrum. The spatio-temporal distributions of electron density and electron temperature were calculated based on radiation hydrodynamic simulation in order to identify the contributions of various ionic states to the UTAs arising from the Er plasmas near 6.x nm.

Extreme ultraviolet spectral characteristic analysis of highly charged ions in laser-produced Cu plasmas

This paper reports the results of spectral measurements and a theoretical analysis of the temporal and spatial evolution of laser-produced Cu plasma in vacuum in the range of 8–14 nm. The time dependence of the extreme ultraviolet band spectrum at different positions near the target surface was obtained and found to be dominated by three broad-band features. The 3p and 3d excitations of Cu5+–Cu9+ ions were calculated using the Hartree–Fock theory with configuration interactions. The characteristics of the spectral line distribution for the 3p–nd and 3d–nf transition arrays were analyzed. Based on the steady-state collisional radiation model and the normalized Boltzmann distribution, the complex spectral structure in the band of 13–14 nm is accurately explained through consistency comparisons and benchmarking between the experimental and theoretical simulation spectra, demonstrating that the structure mainly stems from the overlapping contribution of the 3d–4f and 3p–3d transition arrays for the Cu5+–Cu9+ ions. These results may help in studying the radiation characteristics of isoelectronic series highly-charged ions involving the 3d excitation process.