Collisional Performance of High-Pressure Beams in EMPIRE

We use Sandia’s EMPIRE PIC-DSMC code for modeling electron beam transport through a dense neutral gas. As we scale up from small model problems to large, user-driven simulations with more realistic physics and large physical geometries, we encounter new performance bottlenecks. While collisions are embarrassingly parallel, and scale extremely well, other parts of the code are not. This means that collisions can require significant computation on the actual meshes and processor decompositions being used.

We investigate some methods for performance improvements of DSMC collisions in these situations. First, we look at maximizing re-use of various data objects when dealing with a large number of types of interactions featuring many different species. Second, we explore sub-element parallelism to address extreme amounts of work being concentrated in a small number of elements, where it is not practical to further decompose the domain.