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.
Highlights
Since the early work by Burgess (1964) and others, the important role of dielectronic recombination (DR) in understanding the dynamics of plasma has been widely known, from low-temperature laboratory plasma and fusion and solar plasma to observations of various astrophysical objects and environments
While a few very accurate measurements of DR spectra are known for selected ions (e.g., Schippers et al 2001; Kieslich et al 2003; Schuch et al 2005, Bernhardt et al 2016), more often than not detailed ab initio calculations are required in order to describe the resonances and plasma rate coefficients for a wide range of ions across the periodic table
− Ed−Ei kB Te for high-enough electron energies εd (Chen, 1986). It is this form of the DR plasma rate coefficient that has been utilized in most computations in order to estimate the rate for the dielectronic recombination of ions in plasma
Summary
Since the early work by Burgess (1964) and others, the important role of dielectronic recombination (DR) in understanding the dynamics of plasma has been widely known, from low-temperature laboratory plasma and fusion and solar plasma to observations of various astrophysical objects and environments. Apart from a brief overview of the Jac toolbox (Fritzsche 2019), here we outline two strategies for simulating the DR spectra and rate coefficients for ions with complex shell structure These strategies make use of a correlated representation of all low-lying DR resonances in Section 3.2 and an approximate treatment of the relevant res-. The simple and flexible use of the Jac toolbox will support the astrophysical community to expand their studies toward other ions and simulations
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