Electrostatic coherent structures: The role of the ions dynamics

The Vlasov-Poisson model is the basic framework for the investigation of electrostatic coherent structures (e.g., phase space holes). Directly observed by high resolution space instruments, they are considered as one of the key ingredients of collisionless space and laboratory plasmas. These structures are in general studied numerically in the 1D limit of nonmoving ions eventually leading to a one single final structure (vortex merging). Here we show that, despite the electronic nature of such vortex, the merging process is inhibited by the ions so that many structures are still observed after several ion periods. Furthermore, the ion mass cannot be considered just as a rescaling parameter in the system evolution. Finally, numerical discretization effects significantly influence the nonlinear plasma dynamics even if statistically the number and typical dimension of the structures is unchanged, thus making the results relevant to space observations. (C) 2007 American Institute of Physics.