Algorithmic Breakthroughs in Multiscale Particle-in-Cell Simulations

Large-scale 3D hybrid (electron fluid, kinetic ion) and full electromagnetic PIC simulations have recently emerged as accurate computational tools for predicting energetic particle transport in complex plasma and magnetic configurations. Multiple temporal and spatial scales associated with both plasma and magnetic field inhomogeneities force severe restrictions on the global timestep in these CPU-intense PIC applications. We present two multi-scale approaches intended to relieve these issues. First, we discuss a new asynchronous hybrid code, HYPERS, which discards traditional time stepping in favor of Discrete-Event Simulation (DES). In DES time increments for individual particles and local electromagnetic fields are adaptively selected through limiting per-update changes of their properties. Second, we present a novel subgridding method for full EM-PIC simulations implemented in our EMPOWER code. Both codes are being geared towards production runs on exascale parallel computer architectures.