Debye-screening effect on electron-impact excitation of helium-like Al¹¹⁺ and Fe²⁴⁺ ions

Debye-screening effects on the electron-impact excitation (EIE) processes for the dipole-allowed transition 1s^2 ^1\rm S \to 1s2p ^1P in He-like Al^11+ and Fe^24+ ions are investigated using the fully relativistic distorted-wave methods with the-Hückel (DH) model potential. Debye-screening effects on the continuum-bound (CB) interaction and target ion are discussed, both of which result in reduction of EIE cross sections. This reduction due to screening on the CB interaction is dominant. The non-spherical and spherical DH potentials are adopted for considering the screening effect on the CB interaction. It is found that the spherical DH potential could significantly overestimate the influence of plasma screening on EIE cross sections for multielectron He-like ions.