Topic/Type: 1. Plasma Simulation, Invited

Advances in petascale kinetic plasma simulation with VPIC and Roadrunner

K. J. Bowers, B. J. Albright, L. Yin, W. Daughton, V. Roytershteyn, B. Bergen, T. J. T. Kwan

Los Alamos National Lab / D. E. Shaw Research

VPIC, a first-principles 3d electromagnetic charge-conserving
relativistic kinetic particle-in-cell (PIC) code, was recently adapted to run on Los Alamos\'s Roadrunner, the first supercomputer to break a petaflop (quadrillion floating point operations per second) in the TOP500 supercomputer performance rankings. Due to physical limitations, moving data between and even within modern processors is more time consuming than performing basic computations. Typical PIC implementations require more data motion per computation than other methods often used in supercomputing (e.g. dense matrix, molecular dynamics N-body and Monte-Carlo calculations), but, unlike traditional codes, VPIC was designed from the ground up to minimize data motion. As a result, VPIC can more fully exploit the potential of petascale resources like Roadrunner. For example, VPIC can perform 0.162 billion cold particles pushed and charge-conserving accumulated per second on the heterogeneous multi-core IBM Cell eDP processors used in Roadrunner---equivalent to 0.517 petaflop (s.p.) on all of Roadrunner. During a parameter study of particle trapping physics within the laser-driven hohlraum of inertial confinement fusion experiments, we measured end-to-end sustained performance exceeding 0.374 Pflop/s (s.p.) on 122,240 processing cores (17 of Roadrunner\'s 18 connected units).

Petascale supercomputers like Roadrunner are enabling VPIC simulations of numerous plasma physics phenomena at unprecedented fidelity and scale---using trillions of particles, billions of mesh points and hundreds of thousands processing of cores. We summarize VPIC\'s modeling capabilities, VPIC\'s optimization techniques and Roadrunner\'s computational characteristics. We then discuss three applications enabled by VPIC\'s unprecedented performance on Roadrunner: modeling laser plasma interaction in upcoming inertial confinement fusion experiments at the National Ignition Facility NIF), modeling short-pulse laser GeV ion acceleration, and modeling reconnection in space and laboratory plasmas.

This work was performed under the auspices of the United States
Department of Energy by the Los Alamos National Security LLC Los
Alamos National Laboratory under Contract No. DE-AC52-06NA25396. Work supported in part by the Laboratory Directed Research and Development (LDRD) Program.