3D electromagnetic parallel PIC in nonorthogonal meshes

Summary form only given, as follows. We show results from a code designed to simulate devices such as high power microwave sources with complex three dimensional geometries. The calculations involved require the largest computers available, so the algorithms and code are designed with parallelism in mind. The code runs on the 256 processor Gray T3D parallel supercomputer at JPL, but is designed to be easily portable to other parallel platforms as well. We describe a technique for electromagnetic particle-in-cell (EMPIC) on nonorthogonal meshes in 3 dimensions. The divergence equations and second order convergence for the fields are preserved in this explicit algorithm by locating the quantities on staggered meshes and transforming between fields dotted with face normals and fields dotted with edge vectors. The domain is decomposed into patches, each of which contains a grid that is logically cartesian but potentially nonorthogonal. The patches interact only through their boundaries, and may be distributed arbitrarily on the processors of a parallel computer. The underlying cartesian grid simplifies the structure of the electromagnetic update compared to fully unstructured grids, and allows us to track the particles positions in the underlying cartesian space. Particles are stored with each patch, and are passed to new patches when they move through a boundary. Other than for diagnostics, no global operations are required. We report on the algorithm design, numerics, verification and benchmarking for this code.