Energy loss of heavy ions in dense plasma. II. Nonequilibrium charge states and stopping powers

The effective charge ${\mathit{Z}}_{\mathrm{eff}}$ of fast heavy ions slowing down in hot dense matter is calculated simultaneously with the stopping power dE/dx. The various ionization and recombination processes determining ${\mathit{Z}}_{\mathrm{eff}}$ are discussed, and corresponding rate coefficients are given; particular attention is paid to dielectronic recombination which turns out to be the dominant capture mechanism in highly ionized target material. Important results are (1) the effective charge of heavy ions passing through matter is considerably higher for fully ionized plasma than for cold target matter; (2) in contrast to stopping in cold targets, where ${\mathit{Z}}_{\mathrm{eff}}$ runs through a series of equilibrium charge states essentially determined by the instantaneous projectile velocity, high nonequilibrium charge states of the projectile are found in strongly ionized targets due to reduced recombination and faster stopping; (3) this causes additional range shortening, in some cases by factors 2–7, in particular for relatively low projectile energies (${\mathit{E}}_{\mathrm{ion}}$<2 MeV/u) and target densities (n<${10}^{20}$ ${\mathrm{cm}}^{\mathrm{-}3}$). Typical results for ${\mathit{Z}}_{\mathrm{eff}}$ and dE/dx in this parameter region are presented. They are compared with recent experimental data; new experiments are proposed. Concerning applications to heavy-ion-driven inertial fusion, the described effects become relevant at the end of the range, and some illustrative cases are discussed.