TY - JOUR
T1 - Electron-ion recombination of Mg6 + forming Mg5 + and of Mg7 + forming Mg6 +
T2 - laboratory measurements and theoretical calculations
AU - Lestinsky, M.
AU - Badnell, Nigel
AU - Bernhardt, D.
AU - Bing, D.
AU - Grieser, M.
AU - Hahn, M.
AU - Hoffmann, J.
AU - Jordon-Thaden, B.
AU - Krantz, C.
AU - Novotný, O.
AU - Orlov, D.A.
AU - Repnow, R.
AU - Shornikov, A.
AU - Müller, A.
AU - Schippers, S
AU - Wolf, A.
AU - Savin, D. W.
PY - 2012/9/24
Y1 - 2012/9/24
N2 - 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.
AB - 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.
KW - atomic data
KW - atomic processes
KW - electron-ion recombination
KW - plasma recombination rate coefficient
KW - plasma temperature
KW - plasma modelling codes
KW - cosmic atomic plasma
KW - ionization balance calculations
KW - dielectronic recombination
UR - http://iopscience.iop.org/journal/0004-637X
U2 - 10.1088/0004-637X/758/1/40
DO - 10.1088/0004-637X/758/1/40
M3 - Article
SN - 0004-637X
VL - 40
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 1
M1 - 40
ER -