Michael S. Pindzola

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 2p3/2 − 2p1/2 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.

Atomic data for modelling fusion and astrophysical plasmas

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.

Total and state-selective charge transfer in He2+ + H collisions

Total and state-selective cross sections for charge transfer in ~1–1000 keV/u He2+ + H collisions have been calculated using a variety of theoretical approaches, namely, the classical trajectory Monte Carlo, atomic-orbital close-coupling and lattice, time-dependent Schrodinger equation methods. Comparison of the results with available experimental measurements and other theoretical cross sections indicates the regimes in which each method is most reliable. The present cross sections, tabulated here, and their evaluation in light of existing data, provide a new benchmark for this inelastic channel in the fundamental collision system He2+ + H over a wide range of collision energies and final quantum levels.

Triple differential cross sections for the electron-impact ionization of helium at 102 eV incident energy.

We examine the time-dependent close-coupling (TDCC) approach to electron-impact single ionization of helium and study the convergence properties of our method. As an example, we compare our calculations to recent measurements of the triple differential cross sections from He after 102 eV electron impact, made for asymmetric electron energies and a variety of electron geometries. We find that our calculations compare well to the measurements and to convergent close-coupling calculations.

Strong-field laser ionization of alkali atoms using two-dimensional cylindrical and three-dimensional Cartesian time-dependent Hartree–Fock theory

The time-dependent Schrodinger equation is solved directly for an alkali atom subject to an arbitrarily strong electromagnetic field. Two methods are compared. A tridiagonal finite-difference method is used to solve Schrodinger’s equation on a two-dimensional (2D) cylindrical coordinate lattice, while a finite-element method using odd-order B splines is used to solve Schrodinger’s equation on a three-dimensional (3D) Cartesian coordinate lattice. Multiphoton ionization cross sections are extracted from 2D cylindrical calculations for hydrogen and lithium and then compared with previous perturbation theory results. Single-photon ionization probabilities are compared from 2D cylindrical and 3D Cartesian calculations for hydrogen.

Single and double photoionization of Be and Mg

A new version of the time-dependent close-coupling method is used to calculate the single and double photoionization of the Be and Mg atoms. Total cross sections are calculated using an implicit time propagator with a core orthogonalization method on a variable radial mesh. The double to single photoionization cross section ratios are found to be in good agreement with experiment for both Be and Mg.

Pentuple energy and angle differential cross sections for the electron-impact double ionization of helium

Energy and angle differential cross sections for the electron-impact double ionization of helium are calculated using a non-perturbative time-dependent close-coupling method. Collision probabilities are found by the projection of a time-evolved nine-dimensional coordinate space wavefunction onto fully antisymmetric products of spatial and spin functions representing three outgoing Coulomb waves. At an incident energy of 106 eV, we present double energy differential cross sections and pentuple energy and angle differential cross sections. The pentuple energy and angle differential cross sections are found to be in reasonable agreement with the scaled shapes observed in recent (e, 3e) reaction microscope experiments. Integration of the differential cross sections over all energies and angles yields a total ionization cross section that is also in reasonable agreement with absolute crossed-beams experiments.

Electron-Ion Collisions in the Average-Configuration Distorted-Wave Approximation

Explicit expressions for the electron-impact excitation, ionization, and resonant-recombination cross sections are derived in the average-configuration distorted-wave approximation. Calculations using these expressions are applied to several types of phenomena in electron-ion scattering where comparison with other theoretical methods and experimental measurements can be made,

Electron-impact ionization of the N atom

Electron-impact ionization cross sections for the ground and excited states of the N atom are calculated using the non-perturbative R-matrix with pseudo-states and time-dependent close-coupling (TDCC) methods, as well as the perturbative distorted-wave method. The TDCC and distorted-wave results for the () excited configurations are much larger than for the ground configuration. In all cases the TDCC results are substantially lower than the distorted-wave results. The ionization cross section results will lead to a better understanding of moderately dense astrophysical and laboratory plasmas containing nitrogen.

Lattice, Time-Dependent Schrodinger Equation Approach for Charge Transfer in Collisions of Be4+ with Atomic Hydrogen

A test of the lattice, time-dependent Schrodinger equation (LTDSE) method for treating inelastic ion–atom collisions is performed by treating state-selective charge transfer in 10–1000 keV/u Be4+ + H collisions. This system possesses a greater charge asymmetry of the colliding nuclei than has been treated in previous applications of the method. Consequently, its ability to represent well the dynamical evolution of the electronic wavefunction within the combination of a shallow and a deep potential well with a single coordinate- and momentum-space discretization is tested. New results are also computed using other, standard approaches, the atomic-orbital close-coupling and classical trajectory Monte Carlo methods, to provide comparisons with the LTDSE results owing to their well-established regimes of applicability and behaviours.