Dielectronic recombination strengths and plasma rate coefficients of multiply charged ions

¹ Helmholtz-Institut Jena, Fröbelstieg 3, 07743 Jena, Germany
² GSI Helmholtzzentrum für Schwerionenforschung, 64291 Darmstadt, Germany
e-mail: s.fritzsche@gsi.de
³ Theoretisch-Physikalisches Institut, Friedrich-Schiller-Universität Jena, 07743 Jena, Germany

Received: 30 June 2021
Accepted: 10 September 2021

Abstract

Context. Dielectronic recombination (DR) has been known as the dominant electron-ion recombination process in different astrophysical and laboratory plasmas, and that it determines the level population and ionization balance over a range of temperatures. Apart from a fundamental interest into the details of this process, DR plasma rate coefficients are frequently applied to estimate plasma densities and temperatures, but have been found to be notoriously difficult to calculate as they require good knowledge of the ionic resonances, which are embedded into the continuum of the next higher charges states.

Aims. In this paper we explain and demonstrate how DR resonance strengths and plasma rate coefficients can be readily computed within the framework of the Jena Atomic Calculator (JAC). In contrast to other available codes, the JAC toolbox supports a much simpler handling and control of different approximations, shell structures and temperature regions, for which doubly excited resonances need to be taken into account.

Methods. A multi-configuration Dirac–Hartree–Fock expansion of all atomic states is generated and applied in order to compute the transition rates (radiative and nonradiative) that contribute to the DR process. For the plasma rate coefficients, moreover, a cascade model has been developed that automatically determines and incorporates all doubly excited configurations of interest for the given plasma temperatures.

Results. To demonstrate the quite flexible use of JAC, we discuss and compare the DR of initially fluorine-like Ni¹⁹⁺ ions with previous measurements and computations. Since it is based on Dirac’s equation, the JAC toolbox is suitable for most ions across the periodic table.