National Center for Computational Sciences

Plasmas in fusion reactors are composed of atoms heated to such high temperatures that electrons are stripped off and flow freely within the plasma. A team led by Weixing Wang of Pacific Northwest Nationaol Laboratory will investigate turbulence-driven momentum and energy transport in two fusion reactor designs. The first, found at the National Spherical Torus Experiment (NSTX) at the Princeton Plasma Physics Laboratory, produces a plasma that is shaped like a sphere with a hole through its center . The second, found at the international ITER reactor being developed in Cadarache, France, is a tokamak reactor producing a doughnut-shaped plasma.

The NSTX configuration may have several advantages, including the ability to confine a plasma under higher pressure for a given magnetic field strength and the ability to support smaller, more economical fusion reactors. On the other hand, both NSTX and tokamak reactors report troubling heat loss linked to electron turbulence, a critical problem whose resolution remains elusive.

Wang’s team will carry out unprecedented large-scale, high-resolution simulations of plasma flow in the NSTX using its own general-geometry, Gyrokinetic Tokamak Simulation (GTS) code. GTS takes into account the full three-dimensional geometry of NSTX, and the planned simulations will treat a wider cross section of plasma flow than has previously been attempted. The team will use 20 million hours on ORNL’s Jaguar petascale computer to systematically assess which of the potential electron loss mechanisms plays the most important role in plasma energy transport. In a second simulation, the team will perform a global gyrokinetic simulation of the electrons’ heat loss and gain and of their trajectories within the plasma flow in NXTS experiments. This study will help to validate the model against a modern, well-diagnosed toroidal experiment.