M. S. Pindzola

Dielectronic Recombination Data for Dynamic Finite-Density Plasmas. I; Goals and Methodology

A programme is outlined for the assembly of a comprehensive dielectronic recombination database within the generalized collisional-radiative (GCR) framework. It is valid for modelling ions of elements in dynamic finite-density plasmas such as occur in transient astrophysical plasmas such as solar flares and in the divertors and high transport regions of magnetic fusion devices. The resolution and precision of the data are tuned to spectral analysis and so are sufficient for prediction of the dielectronic recombination contributions to individual spectral line emissivities. The fundamental data are structured according to the format prescriptions of the Atomic Data and Analysis Structure (ADAS) and the production of relevant GCR derived data for application is described and implemented following ADAS. The requirements on the dielectronic recombination database are reviewed and the new data are placed in context and evaluated with respect to older and more approximate treatments. Illustrative results validate the new high-resolution zero-density dielectronic recombination data in comparison with measurements made in heavy-ion storage rings utilizing an electron cooler. We also exemplify the role of the dielectronic data on GCR coefficient behaviour for some representative light and medium weight elements.

R-MATRIX ELECTRON-IMPACT EXCITATION CROSS SECTIONS IN INTERMEDIATE COUPLING : AN MQDT TRANSFORMATION APPROACH

A widely used alternative to a full Breit-Pauli R-matrix calculation of electron-impact excitation is the transformation of S- or K-matrices, calculated in pure LS coupling, to intermediate coupling. Here we present a transformation method, based on multi-channel quantum defect theory (MQDT), that eliminates the problems associated with standard transformation methods and leads to accurate level-to-level electron-impact excitation cross sections. Instead of transforming the physical S- or K-matrices, we employ MQDT to generate unphysical K-matrices in pure LS coupling; we then treat all channels as open and transform these matrices to intermediate coupling. Finally, we generate the physical K-matrices from the intermediate-coupled unphysical K-matrices. To illustrate the accuracy of this method, we compare cross sections for several transitions in determined using: (i) the standard transformation method in which the LS-coupled physical S-matrices are transformed to intermediate coupling; (ii) an MQDT transformation method, used by others, in which the unphysical LS-coupled K-matrices are transformed to pure jK coupling; (iii) our intermediate coupling frame transformation (ICFT) method and (iv) a full Breit-Pauli R-matrix calculation. It is shown that our ICFT method eliminates the problems associated with the other two transformation methods and leads to cross sections that agree very well with those determined from a full Breit-Pauli R-matrix calculation. Furthermore, the ICFT method can be applied to complex atomic systems which are intractable to a full Breit-Pauli calculation.

Dark-soliton states of Bose-Einstein condensates in anisotropic traps

Dark soliton states of Bose-Einstein condensates in harmonic traps are studied both analytically and computationally by the direct solution of the Gross-Pitaevskii equation in three dimensions. The ground and self-consistent excited states are found numerically by relaxation in imaginary time. The energy of a stationary soliton in a harmonic trap is shown to be independent of density and geometry for large numbers of atoms. Large-amplitude field modulation at a frequency resonant with the energy of a dark soliton is found to give rise to a state with multiple vortices. The Bogoliubov excitation spectrum of the soliton state contains complex frequencies, which disappear for sufficiently small numbers of atoms or large transverse confinement. The relationship between these complex modes and the snake instability is investigated numerically by propagation in real time.

Dielectronic recombination data for dynamic finite-density plasmas III. The beryllium isoelectronic sequence

Dielectronic recombination data for the beryllium isoelectronic sequence has been calculated as part of the assembly of a dielectronic recombination database necessary for modelling of dynamic finite-density plasmas (Badnell et al. 2003, A&A, 406, 1151). Dielectronic recombination coecients for a selection of ions from this sequence are presented and the results discussed.

Dielectronic recombination data for dynamic finite-density plasmas - XI : The sodium isoelectronic sequence

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 VI. The boron isoelectronic sequence

We have calculated dielectronic recombination rate coefficients for 22 ions of the boron isoelectronic sequence, between C+ and Xe49+, within the generalized collisional-radiative framework, as outlined by Badnell et al. (2003). Calculations have been performed from both ground and metastable initial states, in both LS- and intermediate-coupling, allowing for Deltan = 0 and Deltan = 1 core-excitations. Results are presented and discussed for a selection of ions from the sequence. Results which are not presented here can be accessed from the Atomic Data and Analysis Structure (ADAS) database (Summers 2003) or from the Oak Ridge Controlled Fusion Atomic Data Center (http://www-cfadc.phy.ornl.gov). Comparison is made with the results of other existing theoretical calculations.

Dielectronic recombination data for dynamic finite-density plasmas V. The lithium isoelectronic sequence

Dielectronic recombination data for the lithium isoelectronic sequence has been calculated as part of the assembly of a dielectronic recombination database necessary for modelling of dynamic finite-density plasmas (Badnell et al. 2003). Dielectronic recombination coefficients for a selection of ions from this sequence are presented and the results discussed.

The time-dependent close-coupling method for atomic and molecular collision processes

We review the development of the time-dependent close-coupling method to study atomic and molecular few body dynamics. Applications include electron and photon collisions with atoms, molecules, and their ions.

Electron-impact cross sections and rate coefficients for excitations of carbon and oxygen ions

Abstract Cross sections have been compiled for electron-impact excitation of carbon and oxygen ions (C II–VI and O II–VIII). A selection has been made to recommend “best” values for use. The resulting recommended values are fitted to an analytical formula and the fitting coefficients are given in a table. The cross sections (in the form of collision strengths) and the rate coefficients calculated therefrom are shown graphically. The reliability of the recommended data is roughly estimated.

The effects of radiative cascades on the x-ray diagnostic lines of Fe16+

We present complete collisional-radiative modelling results for the soft x-ray emission lines of Fe16+ in the 15 A–17 A 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.