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Context. Emission from Ar III is seen in planetary nebulae, in H II regions, and from laboratory plasmas. The analysis of such spectra requires accurate electron impact excitation data.

We have calculated total and partial final-state level-resolved dielectronic recombination (DR) rate coefficients for the ground and metastable initial levels of 21 Mg-like ions between Al+and Xe42+. This is the final part of the assembly of a level-resolved DR database necessary for modelling dynamic finite-density plasmas within the generalized collisional-radiative framework. Calculations have been performed in both LS- and intermediate coupling, allowing for $\Delta n$= 0 and $\Delta n$= 1 core-excitations from ground and metastable levels. Complementary partial and total radiative recombination RR coefficients have been calculated for the same ions viz. Al+through Zn18+, as well as Kr24+, Mo30+, and Xe42+. Fitting coefficients which describe the total RR and DR rate coefficients (separately) are also presented here. Results for a selection of ions from this sequence are discussed, and compared with existing theoretical and experimental results. A full set of results can be accessed from the Atomic Data and Analysis Structure (ADAS) database or from the Oak Ridge Controlled Fusion Atomic Data Center (http://www-cfadc.phy.ornl.gov/data_and_codes). The complexity of further M-shell sequences, both from the atomic and modelling perspectives, renders this juncture a natural conclusion for the assemblage of the partial database. Further M-shell work, has and will, focus more on total rate coefficients, rather than partials, at least in the medium term.

Dielectronic recombination (DR) rate coefficients for 22 sodium-like ions, between Mg+and Xe43+, forming magnesium-like ions have been calculated as part of the assembly of a level-resolved DR database necessary for modelling dynamic finite-density plasmas, within the generalized collisional–radiative framework. Calculations have been performed from both ground and metastable initial states, in both LS- and intermediate coupling, allowing for $\Delta n=0$and $\Delta n=1$core-excitations from ground and metastable levels. Partial and total DR coefficients have been calculated for Mg+to Zn19+, as well as Kr25+, Mo31+, and Xe43+. Results for a selection of ions from the sequence are discussed in the paper and compared with existing theoretical and experimental results. A full set of results can be accessed from the Atomic Data and Analysis Structure (ADAS) database or from the Oak Ridge Controlled Fusion Atomic Data Center (http://www-cfadc.phy.ornl.gov/data_and_codes).

The assumptions underpinning escape probability and absorption factor methods for describing spectral emission from optically thick plasmas, are addressed to test the range of validity of the associated expressions and to develop them for use within non-stratified atmospheres which include plasma flow and line blending. It is found that for moderate optical depths ($\tau_0<$~10) the escape probability is an effective tool for accurately describing the effect of opacity on emergent spectral line intensities. Furthermore it is found that the expressions may be used to extract optical depths directly from observational data independentlyof preconceived atmosphere model ideas. The analysis enables the detection of unresolvedspicule-like structures at the solar limb.

AbstractThere have been long outstanding requests from the modeling community for uncertainty estimates on atomic data. This paper outlines a systematic approach from fundamental atomic structure and collisional calculations, through to well-known spectral diagnostic lines, correlating the uncertainties from each contributing process.

Aims. Merged-beam and plasma recombination rate coefficients for Be-like?Nevii were extracted from results of a merged-beam type experiment.Methods. The cryring heavy-ion storage ring was used to determine merged-beam recombination rate coefficients for Be-like?Ne6+. Recombined Ne5+ions were separated from the stored beam in the first dipole magnet following the electron-ion interaction region. Field-ionization at this dipole magnet prevented detection of recombination into states with the principal quantum number n>ncutoff=23. To account for the field-ionization effects, results obtained with autostructure calculations were used for recombination channels above ncutoff. The merged-beam recombination rate coefficients were then convoluted with Maxwellian electron energy distributions in the 103-3?106?K temperature region, to obtain plasma recombination rate coefficients.Results. Good agreement was found between the experimentally derived rate coefficient spectrum and results of the autostructure calculation. At low energies, several strong dielectronic recombination resonances belonging to the spin-forbidden 2s2p(3PJ)nl series dominate the merged-beam spectrum. Recombination through these states dominates at low-temperatures, e.g. at 103?K recombination through these resonances is more than one order of magnitude higher than the radiative recombination rate coefficient. Most data from the literature significantly underestimate the low-temperature plasma rate coefficients below 104?K, with only two calculations showing rate coefficients comparable to our results.?Strong contributions from trielectronic recombination were found in the merged-beam spectrum of Be-like?Ne, associated with double excitation of the Be-like?Ne core, during the attachment of the free electron. Calculated trielectronic recombination resonance positions agree with experimental peaks, however compared to the experiment, the calculation underestimates the strength of trielectronic recombination.

The paper presents an integrated view of the population structure and its role in establishing the ionization state of light elements in dynamic, finite density, laboratory and astrophysical plasmas. There are four main issues, the generalized collisional-radiative picture for metastables in dynamic plasmas with Maxwellian free electrons and its particularizing to light elements, the methods of bundling and projection for manipulating the population equations, the systematic production/use of state selective fundamental collision data in the metastable resolved picture to all levels for collisonal-radiative modelling and the delivery of appropriate derived coefficients for experiment analysis. The ions of carbon, oxygen and neon are used in illustration. The practical implementation of the methods described here is part of the ADAS Project.

We present complete collisional-radiative modelling results for the soft x-ray emission lines of Fe16+in the 15 Å-17 Å range. These lines have been the subject of much controversy in the astrophysical and laboratory plasma community. Radiative transition rates are generated from fully relativistic atomic structure calculations. Electron-impact excitation cross sections are determined using a fully relativistic R-matrix method employing 139 coupled atomic levels through n= 5. We find that, in all cases, using a simple ratio of the collisional rate coefficient times a radiative branching factor is not sufficient to model the widely used diagnostic line ratios. One has to include the effects of collisional-radiative cascades in a population model to achieve accurate line ratios. Our line ratio results agree well with several previous calculations and reasonably well with tokamak experimental measurements, assuming a Maxwellian electron-energy distribution. Our modelling results for four EBIT line ratios, assuming a narrow Gaussian electron-energy distribution, are in generally poor agreement with all four NIST measurements but are in better agreement with the two LLNL measurements. These results suggest the need for an investigation of the theoretical polarization calculations that are required to interpret the EBIT line ratio measurements.

To test the validity of classical trajectory and perturbative quantal methods for electron-impact ionization of H-like ions from excited states, we have performed advanced close-coupling calculations of ionization from excited states in H, Li²⁺ and B⁴⁺ using the R-matrix with pseudo states and the time-dependent close-coupling methods. Comparisons with our classical trajectory Monte Carlo (CTMC) and distorted-wave (DW) calculations show that the CTMC method is more accurate than the DW method for H, but does not improve with n and grows substantially worse with Z, while the DW method improves with Z and grows worse with n.

To test the validity of classical trajectory and perturbative quantal methods for electron-impact ionization of H-like ions from excited states, we have performed advanced close-coupling calculations of ionization from excited states in H, Li2+and B4+using the R-matrix with pseudo states and the time-dependent close-coupling methods. Comparisons with our classical trajectory Monte Carlo (CTMC) and distorted-wave (DW) calculations show that the CTMC method is more accurate than the DW method for H, but does not improve with nand grows substantially worse with Z, while the DW method improves with Zand grows worse with n.

Trends and focii of interest in atomic modelling and data are identified in connection with recent observations and experiments in fusion and astrophysics. In the fusion domain, spectral observations are included of core, beam penetrated and divertor plasma. The helium beam experiments at JET and the studies with very heavy species at ASDEX and JET are noted. In the astrophysics domain, illustrations are given from the SOHO and CHANDRA spacecraft which span from the solar upper atmosphere, through soft x-rays from comets to supernovae remnants. It is shown that non-Maxwellian, dynamic and possibly optically thick regimes must be considered. The generalized collisional-radiative model properly describes the collisional regime of most astrophysical and laboratory fusion plasmas and yields self-consistent derived data for spectral emission, power balance and ionization state studies. The tuning of this method to routine analysis of the spectral observations is described. A forward look is taken as to how such atomic modelling, and the atomic data which underpin it, ought to evolve to deal with the extended conditions and novel environments of the illustrations. It is noted that atomic physics influences most aspects of fusion and astrophysical plasma behaviour but the effectiveness of analysis depends on the quality of the bi-directional pathway from fundamental data production through atomic/plasma model development to the confrontation with experiment. The principal atomic data capability at JET, and other fusion and astrophysical laboratories, is supplied via the Atomic Data and Analysis Structure (ADAS) Project. The close ties between the various experiments and ADAS have helped in this path of communication.

The plasma in the periphery or in a divertor chamber of a magnetic fusion device plays an important role in the spread of particle and heat power. Optimising the role of such a plasma requires its characterization and the understanding of all the mutual interactions of its constituents (ions, electrons, and neutrals), and also their interactions with the device materials. Among the various diagnostic methods, high-resolution passive spectroscopy is well suitable for such a purpose since it is non-intrusive. However, diagnostics based on this method requires an accurate modelling of the observed spectra. A fitting routine has been developed for the interpretation of Dα spectra measured in front of a neutraliser plate of the Tore-Supra Ergodic Divertor. It takes into account both Zeeman and Doppler effects, the instrumental function, and the relaxation of the neutrals induced by elastic collisions with the plasma ions. On the other side, in order to study high-n Balmer lines and the continuum emission of deuterium in detached divertor plasmas, a more complex lineshape code developed for Stark broadening has been recently coupled to a code accounting for line-merging into the continuum. The code allows the convolution with a Gaussian (or a Lorentzian) to account for the Doppler broadening and the instrumental function. The Stark lineshape code has also been updated to include Zeeman effect and can be used for conditions where both Stark and Zeeman effects are important like in ITER-divertor plasmas.

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Context.Accurate atomic data for the less abundance Fe-peak elements are required for use in X-ray astrophysical studies.