Journal article

Publication year: 2012

Journal: The Astrophysical Journal

Volume number: 758

Issue number: 1

ISSN: 0004-637X

eISSN: 1538-4357

Open access status: Green

DOI Link: https://doi.org/10.1088/0004-637X/758/1/40

Publisher: American Astronomical Society

Abstract: 
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 (Delta N = 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 Delta N = 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.

Harvard Citation style: Lestinsky, M., Badnell, N., Bernhardt, D., Bing, D., Grieser, M., Hahn, M., et al. (2012) Electron-ion recombination of mg6+ forming Mg5+ and of Mg7+ forming Mg6+: Laboratory measurements and theoretical calculations, The Astrophysical Journal, 758(1), Article 40. https://doi.org/10.1088/0004-637X/758/1/40

APA Citation style: Lestinsky, M., Badnell, N., Bernhardt, D., Bing, D., Grieser, M., Hahn, M., Hoffmann, J., Jordon-Thaden, B., Krantz, C., Novotny, O., Orlov, D., Repnow, R., Shornikov, A., Müller, A., Schippers, S., Wolf, A., & Savin, D. (2012). Electron-ion recombination of mg6+ forming Mg5+ and of Mg7+ forming Mg6+: Laboratory measurements and theoretical calculations. The Astrophysical Journal. 758(1), Article 40. https://doi.org/10.1088/0004-637X/758/1/40