Level-resolved Dielectronic Recombination Research Articles

Dielectronic recombination data for dynamic finite-density plasmas

Context.We aim to present a comprehensive theoretical investigation of dielectronic recombination (DR) of the silicon-like isoelectronic sequence and provide DR and radiative recombination (RR) data that can be used within a generalized collisional-radiative modelling framework.Aims.Total and final-state level-resolved DR and RR rate coefficients for the ground and metastable initial levels of 16 ions between P+and Zn16+are determined.Methods.We carried out multi-configurational Breit-Pauli DR calculations for silicon-like ions in the independent processes, isolated resonance, distorted wave approximation. Both Δnc= 0 and Δnc= 1 core excitations are included usingLSand intermediate coupling schemes.Results.Results are presented for a selected number of ions and compared to all other existing theoretical and experimental data. The total dielectronic and radiative recombination rate coefficients for the ground state are presented in tabulated form for easy implementation into spectral modelling codes. These data can also be accessed from the Atomic Data and Analysis Structure (ADAS) OPEN-ADAS database. This work is a part of an assembly of a dielectronic recombination database for the modelling of dynamic finite-density plasmas.

Dielectronic recombination of the open 4d-shell of tungsten: W37+–W28+

Tungsten is an important element for magnetically confined fusion plasmas but has the potential to cool, or even quench the plasma due to it being an efficient radiator. Total and level-resolved dielectronic recombination (DR) rate coefficients, for all ionisation stages, are essential to model tungsten. We describe a set calculations performed using the distorted wave code autostructure for the tungsten ions –. We demonstrate the importance of relativistic configuration mixing in such calculations. In particular, we show that the partial DR rate coefficients calculated in level and configuration resolution can differ by as little as 5%, and up to as much as 75%. Using the new data, we calculate a revised steady-state ionisation fraction for tungsten. We find that, relative to the ionisation fraction calculated using the recombination rate coefficients of Putterich et al (2008 Plasma Phys. Control. Fusion 50 085016), the peak temperatures of – ionisation states are shifted to lower temperatures spanning 0.9–1.6 keV. This temperature range is important for understanding the performance of large tokamaks, such as ITER, because the temperatures in the pedestal, edge, scrape-off-layer and divertor region fall in this range.

Dielectronic recombination of Au20 +: a theoretical description of the resonances at low electron energies

In recent years, there has been significant interest in the dielectronic recombination (DR) of complex ions involving open d and open f subshells. Experimental measurement of DR in Au25 + (Hoffknecht et al 1998 J. Phys. B: At. Mol. Opt. Phys. 31 2415) and W20 + (Schippers et al 2011 Phys. Rev. A 83 012711), both with ground configurations of 4p64d104f8, revealed extremely large and broad resonances at low electron energies. DR in such ions is very difficult to describe in detail theoretically because of the complexity of the recombining resonant states and the source of these resonant structures has not been fully explained for the aforementioned ions. However, a very recent measurement of DR in Au20 + (Schippers et al 2011 Phys. Scr. T 144 014039) with a ground configuration of 4p64d104f13 displayed very large but narrower resonances in the low-energy region. With the somewhat reduced complexity of the recombining resonances in this ion, we have been able to complete the first full intermediate-coupling level-resolved DR calculation for Au20 +. In the low-energy region, we find excellent agreement with the experimental measurements, and have been able to show that the DR rate coefficient in this ion is completely dominated by Δn = 1 transitions and that the low-energy resonances are primarily due to recombining levels of the 4d104f125lnl′ configurations as suggested by Schippers et al (2011 Phys. Scr. T 144 014039) based on atomic structure calculations.

Dielectronic recombination of W35 +

Accurate data for dielectronic recombination (DR) of the ions of tungsten are of significant interest in the modelling of tungsten impurity transport and radiative power loss in current tokamaks and in ITER. However, the complexity of the atomic structure for many of these ions makes level-resolved DR calculations untenable on currently available computers, especially for open d- and f-subshell ions. The majority of DR data presently available for ITER modelling are based on an average-atom approximation. To improve upon these baseline calculations, we investigate the use of the configuration-average distorted-wave (CADW) method to calculate DR rate coefficients for complex open d-shell systems. The aim is to produce rate coefficients that are sufficiently accurate in terms of modelling, yet greatly reduced in term of computational complexity compared to level-resolved calculations. In this paper, we consider the DR of W35 +. Initially, we carry out several large-scale level-resolved calculations for the DR associated with the 4d → 4f and 4p → 4d excitations in this ion, using both the level-resolved distorted-wave and Dirac R-matrix methods. These calculations allow us to test the validity of the CADW approach on these same excitations by comparing cross sections and rate coefficients. These comparisons demonstrate that the CADW method is relatively accurate in relation to these level-resolved methods for the temperature range for which W35 + should exist in a collisionally ionized plasma. We then present results for CADW rate coefficients for both Δn = 0 and Δn = 1 excitations for this ion. This study indicates that it is now feasible to generate a much improved comprehensive set of DR data for the entire tungsten isonuclear sequence.

Dielectronic recombination data for dynamic finite-density plasmas

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 Xe 42+ . This is the final part of the assembly of a levelresolved 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 ∆n = 0a nd∆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 Zn 18+ ,a s well as Kr 24+ ,M o 30+ ,a nd Xe 42+ . 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 data for dynamic finite-density plasmas

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).

Dielectronic recombination data for dynamic finite-density plasmas

Partial and total dielectronic recombination (DR) rate coefficients for fluorine- like ions forming neon-like systems have been calculated as part of the assembly of a final-state level-resolved DR database necessary for the modelling of dynamic finite-density plasmas (Badnell et al. 2003). Calculations have been performed for DR of both ground and metastable initial states for Ne+ to Zn21+, as well as for Kr27+, Mo33+, and Xe45+. Results for a selection of ions are presented and discussed. We find that low-temperature DR, via 2 -> 2 core excitations involving no change in the principal quantum number of the core electron, does not scale smoothly with nuclear charge Z due to resonances straddling the ionization limit of the recombined system, thereby making explicit calculations for each ion necessary. Most of the earlier calculations neglected contributions from the fine-structure 2p(3/2)-2p(1/2) excitation which has been shown to be very important for low-temperature DR coefficients. The DR data are suitable for modelling of solar and cosmic plasmas under conditions of collisional ionization equilibrium, photoionization equilibrium, and non-equilibrium ionization.

Dielectronic recombination data for dynamic finite-density plasmas

Fil: Mitnik, Dario Marcelo. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Ciudad Universitaria. Instituto de Astronomia y Fisica del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomia y Fisica del Espacio; Argentina

Dielectronic recombination data for dynamic finite-density plasmas

Dielectronic recombination (DR) and radiative recombination (RR) data for carbon-like ions forming nitrogen-like ions have been calculated as part of the assembly of a level-resolved DR and RR database necessary for modelling of dynamic finite-density plasmas (Badnell et al. [CITE]). Total DR and RR rate coefficients are presented and the results discussed for N+ to Zn24+, as well as Kr30+, Mo36+, Cd42+, and Xe48+. We find that the (no change in the principal quantum number of the core electron) low-temperature DR does not scale smoothly with nuclear charge Z due to resonances straddling the ionization limit, thereby making explicit calculations for each ion necessary. The RR and DR data are suitable for modelling of solar and cosmic plasmas under conditions of collisional ionization equilibrium, photoionization equilibrium, and non-equilibrium ionization.

Dielectronic recombination data for dynamic finite-density plasmas

Dielectronic recombination (DR) and radiative recombination (RR) data for oxygen-like ions forming fluorine-like ions have been calculated as part of the assembly of a level-resolved DR and RR database necessary for modelling of dynamic finite-density plasmas (Badnell et al. 2003). Total DR and RR rate coecients for F + to Zn 22+ are presented and the results discussed. By comparison between perturbative and R-matrix results, we find that RR/DR interference eects are negligible even for the lowest-charged F + member. We also find that the 2 ! 2 low-temperature DR (no change in the principal quantum number of the core electrons) does not scale smoothly with nuclear charge Z due to resonances straddling the ionization limit, thereby making explicit calculations for each ion necessary. These RR and DR data are suitable for modelling of solar and cosmic plasmas under conditions of collisional ionization equilibrium, photoionization equilibrium, and non-equilibrium ionization.