电子碰撞电离Fe ^（11+）生成Fe ^（12+）和Fe ^（13+）的储存环截面测量
Storage Ring Cross Section Measurements for Electron Impact Ionization of Fe^11+ Forming Fe^12+ and Fe^13+
摘要：
本文报道了Fe ^11 +$电子碰撞单电离（EISI）形成Fe ^12+和Fe ^11+电子碰撞双电离（EIDI）形成Fe ^13+的电离截面测量结果。测量覆盖了从大约230 eV到2300 eV的质心能量范围。实验是使用位于德国海德堡的马克斯-普朗克核物理研究所的重离子储存环TSR进行的。存储环方法允许几乎所有的亚稳能级在数据收集开始之前弛豫到基态。我们发现，单电离的截面是30%小于先前测量的单通实验中使用的离子束与一个未知的亚稳分数。我们还发现我们的实验截面单电离和最近的扭曲波（DW）计算之间的一些显着差异。在Fe ^11+在碰撞电离平衡中含量丰富的温度下，Fe ^11+形成Fe ^12+的DW麦克斯韦EISI速率系数可能被低估了25%。这可能是由于在计算中没有3s激发-自电离（EA）。然而，由于该EA通道而导致的截面的精确测量是不可能的，因为该过程在实验上不能与n=3电子到n > 44的水平的电子碰撞激发以及随后在相互作用区域之后的电荷状态分析器中的场电离区分开。我们的实验结果还表明，双电离截面是占主导地位的间接过程中，直接单电离的内壳层2l电子，其次是自电离，导致净双电离。
英文摘要：
We report ionization cross section measurements for electron impact single ionization (EISI) of Fe^11+$ forming Fe^12+ and electron impact double ionization (EIDI) of Fe^11+ forming Fe^13+. The measurements cover the center-of-mass energy range from approximately 230 eV to 2300 eV. The experiment was performed using the heavy ion storage ring TSR located at the Max-Planck-Institut fur Kernphysik in Heidelberg, Germany. The storage ring approach allows nearly all metastable levels to relax to the ground state before data collection begins. We find that the cross section for single ionization is 30% smaller than was previously measured in a single pass experiment using an ion beam with an unknown metastable fraction. We also find some significant differences between our experimental cross section for single ionization and recent distorted wave (DW) calculations. The DW Maxwellian EISI rate coefficient for Fe^11+ forming Fe^12+ may be underestimated by as much as 25% at temperatures for which Fe^11+ is abundant in collisional ionization equilibrium. This is likely due to the absence of 3s excitation-autoionization (EA) in the calculations. However, a precise measurement of the cross section due to this EA channel was not possible because this process is not distinguishable experimentally from electron impact excitation of an n=3 electron to levels of n > 44 followed by field ionization in the charge state analyzer after the interaction region. Our experimental results also indicate that the double ionization cross section is dominated by the indirect process in which direct single ionization of an inner shell 2l electron is followed by autoionization resulting in a net double ionization.
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