Storage ring cross section measurements for electron impact ionization of Fe⁸⁺

Abstract

We have measured electron impact ionization (EII) for Fe 7+ from the ionization threshold up to 1200 eV. The measurements were performed using the TSR heavy ion storage ring. The ions were stored long enough prior to measurement to remove most metastables, resulting in a beam of 94% ground state ions. Comparing with the previously recommended atomic data, we find that the Arnaud & Raymond (1992) cross section is up to about 40% larger than our measurement, with the largest discrepancies below about 400 eV. The cross section of Dere (2007) agrees to within 10%, which is about the magnitude of the experimental uncertainties. The remaining discrepancies between measurement and the most recent theory are likely due to shortcomings in the theoretical treatment of the excitation-autoionization contribution.

X-ray emission from thin plasmas

“…aa As explained in the previous sections, the most recent experimental measurements included in this work are Fe xviii, Fe xvii, and Fe xiv (Hahn et al 2013), Fe xiii (Hahn et al 2012b), Fe xii (Hahn et al 2011a), Fe xi and Fe x (Hahn et al 2012c), Fe ix (Hahn et al 2016) and Fe viii (Hahn et al 2015), and Bernhardt et al (2014) for Fe xv. They used the new TSR technique to reduce the metastable ion levels to obtain lower cross-sections than AR for all the ions.…”

“…They were obtained from experimental measurements, theoretical calculations, and interpolation/extrapolation among the data sets. We incorporated the most recent experimental measurements available at the moment, taken by Fogle et al (2008), Hahn et al (2011aHahn et al ( ,b, 2012aHahn et al ( ,b,c, 2013Hahn et al ( , 2015Hahn et al ( , 2016, and Bernhardt et al (2014).…”

“…Otherwise, for Fe ix recent measurements of Hahn et al (2016) are available. In this case, the storage ring could not eliminate all the metastable ions from the beam.…”

Single-particle detection of products from atomic and molecular reactions in a cryogenic ion storage ring

“…Eventually, the detector is designed to intercept product particles originating from ion-electron interactions in the future electron cooler of CSR-like electron recombination or electron impact ionisation [32,33]. In contrast to the detector setup, the cooler was not yet operational during the 2015 experiments.…”

Electron-impact ionization of Fe8+

“…The approach used allowed for a significant reduction in the fraction of metastable ions in the beam. Therefore, the measurements were extended to other iron ions, such as Fe 12+ (Hahn et al 2011), Fe 9+ , Fe 10+ (Hahn et al 2012), Fe 13+ , Fe 16+ , Fe 17+ (Hahn et al 2013), Fe 14+ (Bernhardt et al 2014), Fe 7+ (Hahn et al 2015), and Fe 8+ (Hahn et al 2016). Recently, the cross sections for Fe 1+ , Fe 2+ , Fe 3+ , and Fe 4+ ions were produced using the CADW method (Pindzola & Loch 2018).…”