N. R. Badnell

Dielectronic recombination of light Be-like and B-like ions

Dielectronic recombination cross sections from the ground and metastable states of the Be-like ions C2+, O4+ and F5+, and the B-like ions O3+ and F4+, have been calculated and compared with experimental results obtained by a merged-beams technique. The comparison of theory and experiment is complicated by the presence of weak electric fields in the interaction region. However, the authors qualitatively explain the main features of their experimental results. In particular, for Be-like ions they find evidence of a large contribution from the initial 2s2p 3P metastable state recombining into an Auger metastable final state.

Electron impact ionization of Ca

The authors have carried out a number of close-coupling calculations for the electron impact excitation of the 3p53d4s configuration of Ca+ using the R-matrix method, so as to determine the indirect contribution to the ionization of Ca+. They find that the large resonance features primarily due to capture into the 3p53d24s configuration, present when only the 4P and the two 2P terms of the 3p53d4s configuration are included in the continuum close-coupling expansion, disappear when all nine terms of this configuration are included. The resulting ionization cross section is in reasonably good agreement with experiment over the energy range where dielectronic capture-autoionization features could be expected and resolves a long-standing disagreement between theory and experiment.

Electron scattering theory for highly charged ions

Lowest-order QED theory using distorted wave states provides a convenient description for many electron scattering processes involving highly charged atomic ions. We apply QED theory to calculate ionization, excitation, and dielectronic recombination cross sections for electron scattering from highly charged uranium ions. For ionization and dielectronic recombination we compare theory with recent heavy ion accelerator measurements. We also apply lowest-order electroweak gauge theory using distorted wave states to examine the Z-scaling of parity-violating neutral current contributions to the KLL Auger decay of atomic ions.

Dielectronic recombination in atomic ions

The general theory of dielectronic recombination in atomic ions dates back to the seminal work by Bates and Massey in the 1940’s. The predictive power of modern day theory hinges on the incorporation of advanced computational techniques for handling the many reaction pathways found in this particular quantum mechanical many‐body problem. Of recent interest is the comparison of theory with the growing number of high resolution cross section experiments based on mergin electron and ion beams. We will report on the current status of the agreement between isolated resonance theory and electron target experiments performed using either the Aarhus EN Tandem acclerator or the Heidelberg Test Storage Ring. Future directions for both theory and experiment will be suggested.

The R‐matrix approach to atomic collisions

We review briefly the R‐matrix approach to atomic collisions. We then discuss its application to the electron impact excitation of Si3+ and Zn+, and to the excitation‐autoionization of Ca+, and discuss the results in comparison with experiment.

Theoretical calculations of angular distributions of inelastically scattered electrons from multiply charged ions

In this paper, we report on calculations of angular differential cross sections of inelastically scattered electrons. Through example, we show that differential cross sections provide information which is quite useful, particularly in interpreting the new generation of electron‐impact excitation experiments which detect the scattered electrons. It is found that the distribution of angular scattering changes dramatically as a function of electron energy when recombination resonances dominate the excitation cross section. Thus, in these experiments, the angular range of electrons entering the detector must be known with some accuracy in order to determine the cross section in the resonance region. Furthermore, for dipole‐allowed transitions near threshold, the electrons are preferentially back‐scattered; however, the fraction of electrons scattered in the forward direction increases dramatically with energy. The corresponding angular distribution of the scattered electrons for spin‐forbidden transitions app...

High resolution measurement of dielectronic recombination of fluorine‐like Se25+

For the fluorine‐like ion Se25+, which is important in x‐ray laser research, energies and absolute cross sections for dielectronic recombination have been measured in an energy range from 0 up to 2000 eV at the Heidelberg heavy ion storage ring TSR, using the electron cooler as a free electron target. Detailed comparisons with atomic structure calculations have been made.

Beyond the Standard Computational Method for Dielectronic Recombination of Atomic Ions

One of the first benefits from the development of heavy-ion storage-cooler rings1 for atomic and nuclear physics has been the high resolution mapping of the resonance structures associated with the dielectronic recombination (DR) of atomic ions. Much of this experimental data is of the highest quality and permits a detailed comparison with theoretical predictions based on computationally intensive solutions to the many-body and many-reaction-channel physics problem underlying dielectronic recombination. Theory and experiment have now been compared for H-like ions2,3, He-like ions4–8, Li-like ions5,9,10, Be-like ions11, and B-like ions11. For the most part the agreement between theory and the high resolution measurements has been quite good. The object of this short paper is to give the reader an idea of the physics included and the range of applicability of the so far successful standard computational method. We further speculate on various physical effects not included in the method which may be important in explaining remaining discrepancies and in guiding future experimental developments.

Ionization and Recombination in Transition Metal Ions

We discuss atomic data for transition metal ions and its use in the modeling of non-LTE magnetic fusion plasmas.