Using particle-in-cell computer simulation, the expansion of a plasma formed by isothermal evaporation of ions and electrons off a planar wall into a vacuum is investigated. The hydrodynamical and electrical characteristics of the ion and electron expansion flow during and after the emission phase are analyzed. Ion acceleration is investigated in detail. While during the emission phase a considerable part of the electron energy is stored in thermal motion, and cannot be converted to ion energy, this conversion happens almost completely in the post-emission phase. As a result, the velocity distribution of ions is increased at large velocities by several orders of magnitude.
The one-dimensional expansion of a plasma off a planar wall into a vacuum is studied using particle-in-cell computer simulation. Particular emphasis is put on the acceleration of ions in the plasma. Energy transfer from the electronic to the ionic subsystem, the energy spectra of the ions, and the center-of-mass motion of the ion cloud are monitored. Various parameters that influence the acceleration process are studied: the presence of several ion charge states, of neutrals, the effects of a binary mixture of ions, and of a thermal nonequilibrium between ions and electrons.
Using particle-in-cell computer simulation, the processes occurring in a plasma formed by isothermal evaporation of ions and electrons off a planar wall are studied. A simple model to implement three-body recombination is introduced into this scheme; it fulfills momentum and energy conservation and obeys the wellknown dependences of the recombination rate on density and temperature. Ion acceleration processes are investigated, during both the particle emission phase and afterwards, during expansion into vacuum. Recombination strongly enhances ion acceleration, since due to the recombination-heated electron subsystem the expansion-front space-charge field is increased. Spatial segregation of the neutral gas cloud and the plasma cloud is demonstrated.
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.
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