Scientists from the Lawrence Berkeley National Laboratory have released a study that sheds light on factors that influence the behavior of the plasma turbulence that is driven by the heating process used to create fusion energy. These new findings provide answers that not only answer long-standing questions in the field, they will advance our efforts to predict the performance of fusion reactors and take us one step closer to utilizing this alternative energy source.
Over the period of two years, the team used cutting-edge simulations at the National Energy Research Scientific Computing Center (NERSC) in order to better understand how turbulence behaves in a fusion reactor. The study of turbulence in this field has showed discrepancy between theortical predictions and experimental observations of heat loss due to the inability to determine how it contributes to heat loss in the confined plasma.
Using high-resolution multi-scale simulations, the team resolved the numerous turbulence instabilities previously reported and found that interactions between turbulence at the electron scale and at a scale 60 times larger in ions can solve these mismatches.
"For a very long time, the predictions from leading theories have been unable to explain how much heat loss is coming from electrons in fusion plasma," said Nathan Howard, lead author of the paper. "You apply your best theories, but they have underpredicted the amount of heat loss coming from the electrons."
"In this particular work, we have shown that using the coupled model - where you capture both the large-scale and small-scale turbulence simultaneously - you can actually reproduce the experimental electron heat losses, in part because there appear to be strong interactions between the large-scale and small-scale turbulence that weren't well understood previously," he continued.
The team also revealed that the previous expectation that the larger turbulent "swirls" associated with ions would smear out electron-scale swirls is incorrect. Although this happens at times, it is possible for the two scales to coexist and when they do, they have the potential to interact with each other in such a strong manner that heat loss can only be calculated by a simulation that resolves both scales.
"The challenge we are working on right now is figuring out how to get the complicated simulations, which require significant memory size and bandwidth, to work efficiently and scale well on these new platforms so we can continue to study even more complex scenarios," concluded Chris Holland, coauthor of the paper.
The findings were published in the Dec. 17 issue of Nuclear Fusion.
