Performance portability of HPC discovery science software: Fusion energy turbulence simulations at extreme scale

As High Performance Computing Research and Development moves forward on a variety of "path to exascale" architectures today, an associated objective is to demonstrate performance portability of discovery-science-capable software. Important application domains, such as Magnetic Fusion Energy (MFE), have improved modeling of increasingly complex physical systems - especially with respect to reducing "time-to-solution" as well as "energy to solution." The emergence of new insights on confinement scaling in MFE systems has been aided significantly by efficient software capable of harnessing powerful supercomputers to carry out simulations with unprecedented resolution and temporal duration to address increasing problem sizes. Specifically, highly scalable particle-in-cell (PIC) programing methodology is used in this paper to demonstrate how modern scientific applications can achieve efficient architecture-dependent optimizations of performance scaling and code portability for path-to-exascale platforms. Keywords: Turbulence Simulations, Particle-In-Cell, Portability, HPC.