Scientists at PPPL and General Atomics have modeled a self-organized plasma flow that could improve the stability and performance of fusion devices. The research simulates experiments performed on the DIII-D National Fusion Facility that General Atomics operates for the U.S. Department of Energy in San Diego.

The findings, led by PPPL researchers Brian Grierson on site at DIII-D and Weixing Wang in PPPL, demonstrated that sufficient heating of the core of the plasma generates a special type of turbulence that produces an intrinsic torque, or twisting force. This force causes the plasma to self-generate a sheared rotation in which the core and edge of the plasma spin at different rates. It is this sheared rotation, which physicists have traditionally created by injecting high-energy beams of neutral atoms into the plasma, that enhances plasma stability and confinement.

Using the GTS code, for which Wang was primary Theory Department developer, the researchers modeled the behavior of plasma particles as they circled around magnetic fields. The simulation predicted a profile of sheared rotation that agreed quite well, in shape and magnitude, with the rotation observed in DIII-D experiments.

The collaborative results could improve control of fusion reactions in ITER, since neutral beam injection will create only limited rotation in the huge plasma inside the international facility under construction in France. A key next challenge will thus be to extrapolate the processes to ITER, a task that will require massive simulations that will push the limits of supercomputers currently available.