Charge-equilibration of Fe ions accelerated in a hot plasma

Abstract

We examine the energy-dependent rates of charge-changing processes of energetic Fe ions in the hot plasma of the solar corona. For ionization of the Fe-ion projectile in collisions with ambient protons, three different methods of estimating the corresponding ionization cross sections are presented and compared. Proton-impact ionization is found to be significant irrespective of the particular method used. Differences in the proton-impact ionization cross sections' estimates are shown to have little effect in calculating highly nonequilibrium Fe charge states during acceleration, whereas equilibrium charge states are sensitive to such differences. A parametric study of the Fe charge-equilibration comprises (i) impact of the ambient plasma density, and (ii) the energy dependence impact of the acceleration rate upon the charge-energy profiles and upon the estimated values of the density x acceleration-time product. We emphasize potential importance of careful measurements of charge-energy profiles along with ion energy spectra for determining the energy dependence of ion acceleration time and the energy dependence of the leaky-box escape time.