Simulations of Laser-Plasma Interaction from the Full Roadrunner Supercomputer

Isosurfaces of electrostatic field associated with stimulated Raman scattering. The wave fronts exhibit bending or "bowing," arising from nonlinear particle trapping, as well as self-focusing, which breaks up the phase fronts.

In support of the National Ignition Campaign and Laboratory Directed Research and Development, Roadrunner has been used during its open science stabilization phase to perform fully kinetic plasma simulations of laser-plasma interaction (LPI) under conditions encountered in inertial confinement fusion experiments on the National Ignition Facility (NIF).

These simulations employ the VPIC particle-in-cell code and are among the most ambitious ever performed. The largest of these was run on the full Roadrunner system and employed a record 0.4 trillion particles, over 2 billion cells, and ran for nearly 58,160 time steps (nearly 10¹⁹ floating point operations), long enough for two bursts of stimulated Raman scattering, an LPI of critical importance to NIF ignition experiments, to grow from noise to significant amplitude. The figures show isosurfaces of electrostatic field associated with these bursts; the wave fronts exhibit bending or "bowing," arising from nonlinear particle trapping, as well as self-focusing, which breaks up the phase fronts.

This simulation employs the VPIC particle-in-cell code and is among the most ambitious ever performed.

From these basic science simulations, researchers are able to understand better the essential nature of LPI saturation. From this experience, we expect that Roadrunner will for the first time enable three-dimensional ab initio simulations of LPI with rapid turn-around and allow us to model LPI over a range of conditions encountered in fusion ignition experiments. For more information about this Roadrunner open science project, go to "Saturation of Backward Stimulated Scattering of Laser in the Collisional Regime." [LA-UR 09-04450 approved for public release; distribution is unlimited].