A 3-d electrostatic DSMC/PIC model on unstructured grids and applications to plasma microflows

Summary form only given, as follows. A 3-d direct simulation Monte Carlo/collisional-PIC mode on unstructured grid is presented and applied to partially ionized plasmas. Collisions include neutral-neutral, ion-neutrals, charge enhance, and charged particle using the no-time-counter methodology. The results are presented for electrostatic problems and unmagnitized plasmas. Ions and neutrals are modeled as particles. Electrons are modeled by a fluid model at the zero mass limit using a Bolztmann expression. In a second formulation a fully particle approach is utilized. Electric fields are obtained from Poisson's equation. Instead of mapping to a regular domain, each volume is solved for directly through use of the relation of a Delaunay triangulation and its Voronoi dual. Volumes are node-centered with the bounding surface defined by the polygons joining circumcenters of tetrahedra of each edge containing the node of interest. This reduction of a differential equation to a linear problem has several advantages: the only factors important are known geometric quantities and enclosed charge, the faces of a volume are always orthogonal to the line joining the adjacent volumes, and the faces of a volume consist of the set of points closer to the node-centers of the two adjacent volumes than any other points. These considerations give second-order accuracy assuming a Delaunay triangulation. Applications include expanding plasma flows as well as plasma flows in microdomains. Comparisons between the fluid and particle-based electron models are presented.