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For decades, fusion physicists have faced a puzzling contradiction: in large magnetic confinement devices, heat injected at the plasma core appears at the edge almost instantly, defying theories that assume slow, local, diffusive transport. Now, experiments in the Large Helical Device (LHD), one of the world’s largest fusion reactors, have identified the culprit: a special kind of turbulence that behaves like a “passing game” inside the plasma.

Most models had focused on a “running game”: turbulent eddies that gradually carry heat outward, similar to a player running with the ball. The new study shows that there is also a “mediator turbulence” that can link distant regions of the plasma in less than one ten-thousandth of a second, allowing heat to “jump” long distances and reach the edge almost immediately.

To capture this effect, the team used very short heating pulses and high-precision diagnostics with microsecond time resolution to track temperature and turbulence fluctuations. The measurements revealed that shorter pulses strengthen the mediator turbulence and speed up heat propagation, confirming a clearly nonlocal transport regime where rapid long-range interactions dominate.

This discovery not only clarifies a long-standing mystery in fusion research but also offers a new control handle for future reactors. If engineers can dampen the mediator turbulence, they could push the plasma back into a slower, more manageable “running game,” keeping heat confined in the core for longer and moving fusion closer to a practical energy source. Because similar long-range coupling appears in systems such as ocean currents, atmospheric flows, and energy transfer in materials, the results may also influence other areas of physics and climate science.

Main scientific reference link
Technical explainer on the discovery in Interesting Engineering: https://interestingengineering.com/energy/largest-fusion-device-solves-plasma-heat-loss