ELECTRON-ION RECOMBINATION OF Mg^{6 +}FORMING Mg^{5 +}AND OF Mg^{7 +}FORMING Mg^{6 +}: LABORATORY MEASUREMENTS AND THEORETICAL CALCULATIONS

Abstract

We have measured electron-ion recombination for C-like Mg 6+ forming Mg 5+ , and for B-like Mg 7+ forming Mg 6+ . 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 Mg 6+ results, we find that the majority of the stored ions are in a metastable level, while for Mg 7+ the metastable fraction is insignificant. We present the Mg 6+ merged beams recombination rate coefficient for DR via N = 2 → N = 2 core electron excitations (ΔN = 0 DR) and for Mg 7+ 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 Mg 6+ ion beam precludes generating a plasma recombination rate coefficient (PRRC). However, this is not an issue for Mg 7+ and we present an experimentally derived Mg 7+ PRRC for plasma temperatures from 400 K to 10 7 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.

Fusion-Related Ionization and Recombination Data for Tungsten Ions in Low to Moderately High Charge States

“…This can be realized in an ion trap or in an ion storage ring. In order to model the development of excited-level abundances in the W 18+ parent ion beam, a system of coupled rate equations [44] describing population and decay of all levels considered in this treatment was solved numerically using the calculated transition lifetimes. Right after the production of the ions in the stripper foil, at time zero, a Maxwell-Boltzmann distribution of the levels was assumed.…”

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

“…The experimental procedures were similar to those applied in previous measurements [11,[30][31][32] (and references therein). Here we focus on the details that are specific to the present measurements.…”

“…Furthermore, we assumed that the foil-stripping process produced a Boltzmann distribution of initial populations [31] of all 141 levels. The resulting population curves are shown in figure 1.…”

Absolute rate coefficients for photorecombination of beryllium-like and boron-like silicon ions

“…The boron isoelectronic sequence has been less intensely studied. DR rate coefficients from storage-ring experiments are available for C + [30], Ne 3+ [31], Mg 7+ [32], Ar 13+ [33,34], and Fe 21+ [35,36]. State-of-the-art theoretical DR (and TR) calculations have been carried out by Colgan et al [37] and by Altun et al [38,39], respectively, for Be-like and B-like ions of astrophysical interest with the nuclear charge ranging up to Z = 54.…”