 |
Center for Nonlinear Studies |
Knowing the speed at which positively charged ions leave a plasma is essential for accurate modeling of both plasma-materials interactions and global plasma characteristics. This affects laboratory plasmas, particularly in the areas of diagnostics and materials processing, as well as the interaction of space plasmas with spacecraft. Although it has long been agreed upon that ions leave a plasma at the ion acoustic speed when a single ion species is present, a consensus between experiments, theory and simulations has remained elusive when two or more ion species are present. This is a critical issue because plasmas often contain a mixture of ion species. Using a combination of particle-in-cell Monte Carlo collision (PIC-MCC) simulations and theoretical analysis, we show that ion-ion two-stream instabilities can arise near plasma boundaries. These strongly influence the ion speeds by increasing the collisional coupling, and hence friction, between the ion species. By accurately accounting for the instability threshold condition, we show that previously reported disagreements between experiments, simulation and theory can be reconciled.
Host: Jermoe Daligault