World’s largest fusion device solves key plasma heat loss challenge

Researchers at Japan’s National Institute for Fusion Science (NIFS) have solved a longstanding puzzle in fusion reactor physics regarding the rapid heat loss from the plasma core to the edge, which occurs much faster than conventional diffusion theory predicts. Using the Large Helical Device (LHD), the team discovered that plasma turbulence operates in two modes: a slow, local “running game” and a fast, long-range “passing game.” The latter, described as a mediator turbulence, enables heat to leap across distant regions of the reactor almost instantly—within a ten-thousandth of a second—bypassing the space in between and undermining magnetic confinement. To capture this rapid phenomenon, the researchers applied short, intense heating pulses and employed high-precision diagnostics capable of microsecond resolution. Their data confirmed that shorter heating pulses amplify the mediator turbulence, accelerating heat loss. This insight transforms the understanding of plasma turbulence from a chaotic process to a complex system with dual roles in heat transport. Crucially, identifying this mediator