Fusion Reactor 'Flaw' Found to Suppress Turbulence

Physicists working at the DIII-D National Fusion Facility in San Diego have found that a type of plasma wave long blamed for destabilizing fusion reactors can actually help control the turbulence that drains heat from the plasma core. The result, published in Physical Review Letters on September 1, 2026, offers a new tool for improving the performance of tokamak fusion reactors.

The waves in question, called Alfvén eigenmodes, are triggered by fast-moving charged particles inside a tokamak's magnetic bottle. For decades they have been treated mainly as a nuisance capable of expelling energetic particles and cooling the plasma before fusion reactions can occur. The new study shows they have an overlooked upside.

Using a diagnostic called the Motional Stark Effect, which tracks how a beam of neutral deuterium atoms polarizes light as it crosses the plasma's magnetic field, the DIII-D team measured electric currents driven by the eigenmodes that generate a narrow shear-flow layer. That shear was strong enough to fully suppress the small-scale turbulence responsible for leaking heat out of the plasma core, producing a measured 5 percent shift in the plasma's safety factor over about 20 milliseconds and raising both electron and ion temperatures.

Because turbulence-driven heat loss is one of the main obstacles to building an economical fusion power plant, researchers say the self-regulating effect could eventually be tuned deliberately to keep reactor plasmas hotter for longer, rather than being suppressed as an unwanted instability.