Classical Molecular Dynamics Model for Coupled Two-Component Plasmas – Ionization Balance and Time Considerations
Résumé
The dynamic properties of ion-electron two-component plasmas (TCP) are studied by using classical molecular dynamics (MD) simulations. There is a variety of time dependent and structural results that MD is able to provide in complement to other methods, e.g., useful micro-field sequences can be generated. The method deals with some specific difficulties: the mass ratio between ions and electrons enforces very small time-steps appropriate to follow electrons motion while, ions must move significantly in order to build, self consistently, their spatial structure. This results in expensive simulations. Electron trajectories are trapped and de-trapped with multiple electron collisions around ions resulting in the occurrence of quasi metastable bound electron states. An analysis of micro-fields at neutral in a hydrogen plasma reveals the need to consider a complete hierarchy of time scales extended typically over 7 order of magnitude, i.e., from a time-step: 10^-19s, to a time required to obtain statistical averages, 10^-11s. In order to extend the MD capabilities in representing real coupled plasmas a classical ionization/recombination process has been implemented allowing to follow the evolution of plasmas involving several ion stages and model the ionization balance. Here again TCP simulations deal with extended time-scale providing information about relaxation of non equilibrium plasma states