Particle-in-cell study of charge-state segregation in expanding plasmas due to three-body recombination

Using particle-in-cell computer simulation, we perform a model study to determine the effects of recombination processes in an expanding plasma. The model assumes the desorption of a quasi-neutral plasma consisting of doubly charged ions and electrons off a planar wall into vacuum. Three-body recombination will generate singly charged ions. By following in detail the space- and time-dependence of the recombination, and in particular the acceleration by the self-consistently generated electrostatic space-charge field, we demonstrate the ion separation in the expanding plasma. Singly and doubly charged ions are spatially segregated; furthermore, their velocity spectra are pronouncedly different.