Cowan Atomic Structure Research Articles

Investigation of temporal-resolved spectra of laser-produced titanium plasmas

SynopsisLaser-produced titanium (Ti) plasmas have been measured using temporal-spatially resolved laser-produced plasma emission spectroscopy technique. The emission peaks in the wavelength range of 7.5-15 nm were identified from the 3s-(4,5)p, 3p-4d, and 3d-4f transition lines from Ti5+ to Ti11+ ions with aid of NIST database and Cowan atomic structure calculations, as well as comparative analysis between experimental and simulated spectra based on a simplified radiation hydrodynamic model.

Laser gain calculations for soft X-ray and XUV radiation emitted from copper-like ions by electron collisional pumping

Electron impact excitation rate coefficients, level population densities, and gain coefficients for six excited ions with Z = 51, 52, 53, 54, 55, 56 in the copper isoelectronic sequence have been calculated. The electron collisional excitation rate coefficients are calculated according to the analytical formulas of Vriens and Smeets. Fine structure energy levels, transition probabilities, and oscillator strengths needed in the calculations have been calculated using Cowan atomic structure code with relativistic corrections for [Ar]3d10nl with n = 4–7 and l = 0–6. The level population densities are calculated by solving the coupled rate equations involving 30 levels. Positive gain coefficients of the possible emitted lines are obtained at three selected electron temperatures, namely 1/4, 1/2, and 3/4 of the ionization energy. The present calculated data show promising values for the production of soft X-ray and XUV laser by collisional pumping for the transitions 5p–5s and 6d–5f with wavelengths between 108 and 571 Å. The values of the maximum gain coefficient are found to increase with atomic number and their order of magnitude ranges from102to 104cm−1.

Atomic Data and Laser Transitions in as - Like Gallium

Fine structure calculations of the energy levels, the wavelengths, the oscillator strengths, log gf and the transition probabilities for transitions among the terms belonging to 1s2 2s2 2p6 3s2 3p6 3d104s2ns, n=5-6, 1s2 2s2 2p6 3s2 3p6 3d104s2np, n=4-6, 1s2 2s2 2p6 3s2 3p6 3d104s2nd, n=4-6 and1s2 2s2 2p6 3s2 3p6 3d104s2nf, n=4-6 configurations of As (III) have been calculated using configurations interaction Cowan atomic structure code. Our calculated values for the above mentioned quantities have been compared with the corresponding experimental data and other theoretical calculations where a satisfactory agreement is found. We also report on some unpublished values for energy levels, oscillator strengths and transition probabilities for As like gallium. These atomic data are taken as the basis for studying laser transitions between levels of As(III). Excitation rate coefficients of As like gallium are calculated using the analytical formulas of Vriens and Smeets (1980) and with considering using the collisional radiative model code CRMO of Allam (2006). A simple modification to these formulas has been included by introducing effective quantum numbers. The energy values, the radiative data and rate coefficients are then used to calculate the population densities by solving the coupled rate equations. Among these calculations positive gain coefficients are found at three selected values of electron temperature, namely 7.087 eV, 14.147 eV and 21.261 eV which are displayed as a function of the electron impact density.

Influence of the plasma environment on atomic structure using an ion-sphere model

Plasma environment effects on atomic structure are analyzed using various atomic structure codes. To monitor the effect of high free-electron density or low temperatures, Fermi-Dirac and Maxwell-Boltzmann statistics are compared. After a discussion of the implementation of the Fermi-Dirac approach within the ion-sphere model, several applications are considered. In order to check the consistency of the modifications brought here to extant codes, calculations have been performed using the Los Alamos Cowan Atomic Structure (cats) code in its Hartree-Fock or Hartree-Fock-Slater form and the parametric potential Flexible Atomic Code (fac). The ground-state energy shifts due to the plasma effects for the six most ionized aluminum ions have been calculated using the fac and cats codes and fairly agree. For the intercombination resonance line in ${\mathrm{Fe}}^{22+}$, the plasma effect within the uniform electron gas model results in a positive shift that agrees with the multiconfiguration Dirac-Fock value of B. Saha and S. Fritzsche [J. Phys. B 40, 259 (2007)]. Last, the present model is compared to experimental data in titanium measured on the terawatt Astra facility and provides values for electron temperature and density in agreement with the maria code.

Light element opacities from ATOMIC

We present new calculations of local-thermodynamic-equilibrium (LTE) light element opacities from the Los Alamos ATOMIC code. ATOMIC is a multi-purpose code that can generate LTE or non-LTE quantities of interest at various levels of approximation. A program of work is currently underway to compute new LTE opacity data for all elements H through Zn. New opacity tables for H through Ne are complete, and a new Fe opacity table will be available soon. Our calculations, which include fine-structure detail, represent a systematic improvement over previous Los Alamos opacity calculations using the LEDCOP legacy code. Our opacity calculations incorporate atomic structure data computed from the CATS code, which is based on Cowan's atomic structure codes, and photoionization cross section data computed from the Los Alamos ionization code GIPPER. We make use of a new equation-of-state (EOS) model based on the chemical picture. ATOMIC incorporates some physics packages from LEDCOP and also includes additional physical processes, such as improved free–free cross sections and additional scattering mechanisms. In this report, we briefly discuss the physics improvements included in our new opacity calculations and present comparisons of our new opacities with other work for C, O, and Fe at selected conditions.

Atomic decay data for modeling K lines of iron peak and light odd-Zelements

Complete data sets of level energies, transition wavelengths, A-values, radiative and Auger widths and fluorescence yields for K-vacancy levels of the F, Na, P, Cl, K, Sc, Ti, V, Cr, Mn, Co, Cu and Zn isonuclear sequences have been computed by a Hartree-Fock method that includes relativistic corrections as implemented in Cowan's atomic structure computer suite. The atomic parameters for more than 3 million fine-structure K lines have been determined. Ions with electron number N greater than 9 are treated for the first time, and detailed comparisons with available measurements and theoretical data for ions with N less than or equal to 9 are carried out in order to estimate reliable accuracy ratings.

Photoionization cross sections for ions of the cerium isonuclear sequence

Photoionization cross sections for ${\text{Ce}}^{q+}$ $(1\ensuremath{\le}q\ensuremath{\le}9)$ ions were measured in the 105--180 eV energy range of the $4d$ inner-shell giant resonance by merging a mass-to-charge-ratio-selected ion beam with a beam of monochromatized synchrotron radiation. The Cowan atomic structure code was used as an aid to interpret the experimental data. Four Rydberg series for $4d\ensuremath{\rightarrow}nf$ $(n\ensuremath{\ge}4)$ and $4d\ensuremath{\rightarrow}np$ $(n\ensuremath{\ge}6)$ autoionizing excitations were assigned using the quantum-defect theory in the ${\text{Ce}}^{3+}$ photoionization cross section. The experimental data show the collapse of the $nf$ wave functions $(n\ensuremath{\ge}4)$ with increasing ionization stage as outer-shell electrons are stripped from the parent ion. The $nf$ orbital collapse occurs partially for ${\text{Ce}}^{2+}$ and ${\text{Ce}}^{3+}$ ions and completely for ${\text{Ce}}^{4+}$, where these wave functions penetrate the core region of the ion. A strong contribution to the total oscillator strength was observed in multiple photoionization channels for ${\text{Ce}}^{+}$, ${\text{Ce}}^{2+}$, and ${\text{Ce}}^{3+}$, whereas most of the $4d$ excitations of the higher charge states decay by ejection of one electron.

Photoionization and electron-impact ionization ofKr3+

Absolute photoionization cross sections for ${\mathrm{Kr}}^{3+}$ were measured in the energy range $39.05--143.2\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ for single ionization and $120.6--137.7\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ for double ionization. For comparison, an electron-impact single-ionization measurement was made in the energy range $43.1--179.1\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ and normalized to previously published absolute measurements. The Flexible Atomic Code and Cowan atomic structure codes were used to calculate energy levels, excitation energies and oscillator strengths for $3d\ensuremath{\rightarrow}np$, $3d\ensuremath{\rightarrow}nf$, and $4s\ensuremath{\rightarrow}np$ autoionizing transitions from the ground and metastable states. From the single-photoionization measurements, ionization thresholds of the $^{2}P^{o}_{3∕2}$, $^{2}D^{o}_{5∕2}$ metastable states and $^{4}S^{o}_{3∕2}$ ground state were measured to be $46.62\ifmmode\pm\else\textpm\fi{}0.02$, $48.59\ifmmode\pm\else\textpm\fi{}0.01$, and $50.70\ifmmode\pm\else\textpm\fi{}0.02\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$, nearly $2\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ lower than National Institute of Standards and Technology tabulated values. Within the experimental uncertainty, oscillator strengths determined from the photoionization measurements are in agreement with both calculations. Excitation-autoionization and resonant-excitation double-autoionization features are evident in the electron-impact ionization cross section.

Mixed UTA and detailed line treatment for mid-Z opacity and spectral calculations

We developed a method to mix detailed and statistical treatments within the same transition array and for a set of transition arrays entering the spectral or opacity calculations of light and mid-Z elements. By retaining the strongest lines within a given transition array, the method provides a spectral description comparable in accuracy to a detailed treatment approach, where all the lines are explicitly included in the spectral calculation. The remaining weak lines are represented by a UTA-like functional form. Overall, we show that the computational cost approaches the statistical UTA method. The method has been implemented in the Cowan atomic structure code and applied to the calculation of the LTE and non-LTE spectra of two mid-Z elements, xenon and iron.

Photoionization and electron-impact ionization ofKr5+

Absolute photoionization cross sections for ${\mathrm{Kr}}^{5+}$ were measured in the photon energy range $74\char21{}175\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ using synchrotron radiation. For comparison, a detailed energy scan of the electron-impact ionization cross section was made in the same energy range and normalized to previously published absolute measurements. The Flexible Atomic Code and Cowan atomic structure code were used to calculate energy levels, excitation energies, and oscillator strengths for $3d\ensuremath{\rightarrow}np$, $3\mathrm{d}\ensuremath{\rightarrow}nf$, and $4s\ensuremath{\rightarrow}np$ autoionizing transitions from the ground and metastable states. Within the experimental uncertainty, oscillator strengths determined from the photoionization measurements are in agreement with both calculations. Excitation-autoionization and resonant excitation-double-autoionization features are evident in the electron-impact ionization cross section.