Los Alamos scientists Lin Yin and Brian Albright of Applied Science and Method Development, along with Los Alamos guest scientist Kevin Bowers, are using an adapted version of VPIC, a particle-in-cell plasma physics code, on Roadrunner to model the non-linear physics of laser backscatter energy transfer and plasma instabilities to assist colleagues at Lawrence Livermore National Laboratory as they attempt to reach fusion ignition at the National Ignition Facility (NIF) next year.

"These are the largest plasma simulations ever done, looking at 0.4 trillion particles on the whole system", stated Lin Yin. "It would not be possible to do this without a petascale computer like Roadrunner, but even so, we are still only looking at a tiny segment of a laser beam."

VPIC is a computer code that models plasma at very high resolution, so even with Roadrunner it cannot simulate non-linear backscatter in a full laser beam. "And so we focus on a single 'hot spot' in the laser beam to see if we can determine how the energy loss happens and what the non-linear process is", stated Lin Yin.

Energy loss from laser reflectivity depends on laser intensity. This behaviour has been observed in Roadrunner simulations and experiments using the Trident Laser at Los Alamos.