Fusion energy promises a future of clean, nearly limitless power, but building reactors that can survive the extreme conditions inside them remains a major challenge.
New research suggests that the way superhot plasma spins inside fusion machines could be crucial for protecting key components and making reactors last for decades.
Fusion experiments often use devices called tokamaks, doughnut-shaped machines that confine plasma — a superheated gas of charged particles — using powerful magnetic fields.
Inside a tokamak, plasma can reach temperatures hotter than the sun’s core. Keeping this plasma stable and contained is essential for producing energy.
Some plasma inevitably escapes the magnetic field and flows toward a special exhaust system called the divertor.
The divertor is designed to handle this exhaust, where particles strike metal plates, cool down, and bounce back into the plasma, helping maintain the reaction.
Because these plates face intense heat and particle bombardment, engineers must know exactly where the plasma will land to design materials that can withstand the stress.
For years, scientists noticed a puzzling pattern. Much more plasma consistently hits the inner side of the divertor than the outer side. Understanding why this imbalance occurs is important for designing future reactors, but previous computer simulations struggled to reproduce the pattern seen in experiments.
Researchers once believed that the uneven distribution was caused mainly by “cross-field drifts,” a sideways movement of particles across magnetic field lines near the exhaust region.
However, simulations that included only this effect did not match real-world data, raising doubts about whether computer models could reliably guide reactor design.
A new study led by scientists at the U.S. Department of Energy’s Princeton Plasma Physics Laboratory offers a solution. Using advanced simulations, the team discovered that the rotation of plasma around the tokamak plays a major role. As plasma circulates through the machine at tremendous speeds, this motion influences how particles travel toward the divertor.
The researchers simulated plasma behavior in the DIII-D tokamak in California under different conditions. Only when they included both cross-field drifts and the fast rotation of the plasma core did the simulations match the experimental observations. The core rotation they measured reached about 88 kilometers per second, showing just how dynamic the plasma environment is.
The findings reveal that particle motion along magnetic field lines, driven by the spinning plasma, is just as important as sideways motion across those lines. Together, these effects determine where the exhaust particles end up.
This discovery could have significant implications for future fusion power plants. If engineers can accurately predict where the hottest plasma will strike, they can design divertors that are better protected against damage. That, in turn, would help reactors operate reliably for long periods without needing frequent repairs.
Fusion energy still faces many technical hurdles, but understanding the complex behavior of plasma is a major step forward.
By uncovering the role of plasma rotation, scientists have improved the tools needed to design machines that could one day provide safe, sustainable energy for the world.
