Dielectronic recombination data for astrophysical applications: Plasma rate-coefficients for Fe^q+ (q=7-10, 13-22) and Ni^25+ ions from storage-ring experiments

Abstract

This review summarizes the present status of an ongoing experimental effort to provide reliable rate coefficients for dielectronic recombination of highly charged iron ions for the modeling of astrophysical and other plasmas. The experimental work has been carried out over more than a decade at the heavy-ion storage-ring TSR of the Max-Planck-Institute for Nuclear Physics in Heidelberg, Germany. The experimental and data reduction procedures are outlined. The role of previously disregarded processes such as fine-structure core excitations and trielectronic recombination is highlighted. Plasma rate coefficients for dielectronic recombination of Fe q+ ions (q=7-10, 13-22) and Ni 25+ are presented graphically and in a simple parameterized form allowing for easy use in plasma modeling codes. It is concluded that storage-ring experiments are presently the only source for reliable low-temperature dielectronic recombination rate-coefficients of complex ions.

Absolute rate coefficients for photorecombination and electron-impact ionization of magnesiumlike iron ions from measurements at a heavy-ion storage ring

“…Absolute rate coefficients for DR of Fe 14+ ([Ne] 3s 2 1 S 0 ) ions forming Fe 13+ and for EII of Fe 14+ ([Ne] 3s 2 1 S 0 ) ions forming Fe 15+ have been derived from storage ring measurements. The present results together with our previous results for other Fe-M-shell and Fe-L-shell ions [7,8] (and references therein) are relevant for the modelling of the charge balances in photoionized plasmas (PP) and collisionally ionized plasmas (CP). Moreover, the present results benchmark the most recent theoretical calculations for DR [12] and EII [13] of Fe 14+ .…”

“…High-quality atomic data are required for a meaningful interpretation of the observed spectra [3,4]. As part of our ongoing effort to provide reliable ionization and recombination data for astrophysical applications [5][6][7][8] we here present new experimental rate coefficients for photorecombination (PR) and electron-impact ionization (EII) of Mg-like Fe 14+ ions forming Fe 13+ and Fe 15+ , respectively.…”

“…The numbers in the square brackets denote powers of 10. The value for E0 that is to be used in Eqs (7). and (8) is 456.2 eV.…”

Modeling of Photoionized Plasmas

“…This suggestion was confirmed, qualitatively, by (Badnell 2006), who performed distorted wave calculations of the rates and obtained rate coefficients which were even greater than those suggested by (Netzer 2004). Experimental confirmation was demonstrated for Fe 13+ (Schmidt et al 2006), and laboratory measurements have been made for ions down to Fe 7+ (Schippers et al 2010).…”

Storage-ring ionization and recombination experiments with multiply charged ions relevant to astrophysical and fusion plasmas

“…Iron is the most abundant heavy element and still contributes to line emission from astrophysical plasmas when lighter elements are already fully stripped. The present status of the experimentally-derived Fe-DR data base has been summarized recently [3]. A more comprehensive tabulation of storage-ring recombination experiments with astrophysically relevant ions can be found in [4].…”