Plasma-screening effects on electron-impact excitation of hydrogenic ions in dense plasmas

Debye-Hückel and ion-sphere plasma screening models have been used in a study of inelastic scattering of electrons by one-electron ions in dense, high-temperature plasmas. Cross sections for transitions among the $1s$, $2s$, and $2p$ states have been calculated using close-coupling and distorted-wave descriptions. The optically allowed $1s\to 2p$ and $2s\to 2p$ cross sections are substantially reduced at all energies by plasma screening of the long-range dipole coupling. The $1s\to 2s$ cross section is less sensitive to plasma effects. For an ion of nuclear charge $Z$, the scaled inelastic cross sections $Z^{4}Q$ are roughly independent of $Z$ for fixed values of $\frac{E}{Z^2}$ and $Z\Lambda$ or $Z{R}_z$, where $E$ is the electron's kinetic energy, $\Lambda$ is the Debye length, and $R_z$ is the ion-sphere radius.