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

We have measured electron impact ionization (EII) for Fe⁸⁺ forming Fe⁹⁺ from below the ionization threshold to 1200 eV. These measurements were carried out at the TSR heavy ion storage ring. The objective of using a storage ring is to store the ion beam initially so that metastable levels decay, thereby allowing for measurements on a well-defined ground-level ion beam. In this case, however, some metastable levels were too long lived to be removed. We discuss several methods for quantifying the metastable fraction, which we estimate to be ~30%–40%. Although metastables remain problematic, the present storage ring work improves upon other experimental geometries by limiting the metastable contamination to only a few long-lived excited levels. We discuss some future prospects for obtaining improved measurements of Fe⁸⁺ and other ions with long-lived metastable levels. In the attached file, the first column is collision energy in eV, the second column is cross section in cm^-2, and the last column gives the statistical uncertainty.

我们测量了Fe⁸⁺形成Fe⁹⁺过程中的电子碰撞电离（electron impact ionization, EII），能量范围从电离阈值以下到1200 eV。这些测量在TSR重离子储存环上进行。使用储存环的目的是初始储存离子束，使亚稳态能级衰变，从而能够对定义明确的基态离子束开展测量。然而，本研究中部分亚稳态能级寿命过长，无法消除。我们讨论了几种量化亚稳态分数的方法，估计其比例约为30%–40%。尽管亚稳态仍存在问题，但本储存环研究通过将亚稳态污染限制在少数长寿命激发态，改进了其他实验几何构型。我们还探讨了未来对Fe⁸⁺及其他具有长寿命亚稳态的离子进行改进测量的前景。附件文件中，第一列为碰撞能量（单位：eV），第二列为截面（单位：cm⁻²），最后一列为统计不确定度。