Academic Commons

Articles

Electron-Ion Recombination of Mg6 + Forming Mg5 + and Of Mg7 + Forming Mg6 +: Laboratory Measurements and Theoretical Calculations

Lestinsky, M.; Badnell, N. R.; Bernhardt, D.; Grieser, M.; Bing, D.; Hahn, Michael; Hoffman, J.; Jordon-Thaden, B.; Krantz, C.; Novotny, Oldrich; Orlov, D. A.; Repnow, R.; Shornikov, A.; Muller, A.; Schippers, S.; Wolf, A.; Savin, Daniel Wolf

We have measured electron-ion recombination for C-like Mg6 + forming Mg5 +, and for B-like Mg7 + forming Mg6 +. These studies were performed using a merged electron-ion beam arrangement at the TSR heavy ion storage ring located in Heidelberg, Germany. Both primary ions have metastable levels with significant lifetimes. Using a simple cascade model we estimate the population fractions in these metastable levels. For the Mg6 + results, we find that the majority of the stored ions are in a metastable level, while for Mg7 + the metastable fraction is insignificant. We present the Mg6 + merged beams recombination rate coefficient for DR via N = 2 → N' = 2 core electron excitations (ΔN = 0 DR) and for Mg7 + via 2 → 2 and 2 → 3 core excitations. Taking the estimated metastable populations into account, we compare our results to state-of-the-art multiconfiguration Breit-Pauli theoretical calculations. Significant differences are found at low energies where theory is known to be unreliable. Moreover, for both ions we observe a discrepancy between experiment and theory for ΔN = 0 DR involving capture into high-n Rydberg levels and where the stabilization is primarily due to a radiative transition of the excited core electron. This is consistent with previous DR experiments on M-shell iron ions which were performed at TSR. The large metastable content of the Mg6 + ion beam precludes generating a plasma recombination rate coefficient (PRRC). However, this is not an issue for Mg7 + and we present an experimentally derived Mg7 + PRRC for plasma temperatures from 400 K to 107 K with an estimated uncertainty of less than 27% at a 90% confidence level. We also provide a fit to our experimentally derived PRRC for use in plasma modeling codes.

Files

  • thumnail for Lestinsky2012ApJ758_40.pdf Lestinsky2012ApJ758_40.pdf application/pdf 822 KB Download File

Also Published In

Title
The Astrophysical Journal
DOI
https://doi.org/10.1088/0004-637X/758/1/40

More About This Work

Academic Units
Astronomy and Astrophysics
Published Here
March 22, 2013
Academic Commons provides global access to research and scholarship produced at Columbia University, Barnard College, Teachers College, Union Theological Seminary and Jewish Theological Seminary. Academic Commons is managed by the Columbia University Libraries.