Producing fusion energy requires heating plasma to more than one hundred million degrees and confining it stably with strong magnetic fields. However, plasma naturally develops fluctuations known as turbulence, and they carry heat outward and weaken confinement. Understanding how heat and turbulence spread is therefore essential.
Conventional theory has assumed that heat and turbulence move gradually from the center toward the edge. Yet experiments have sometimes shown heat and turbulence spreading much faster, similar to American football players passing a ball quickly across long distances so that a local change influences the entire field almost at once. Clarifying the cause of this rapid, long-range response has been a long-standing challenge.
A research team from the National Institute for Fusion Science carried out short-duration heating of the plasma core in the Large Helical Device and used high-precision diagnostic instruments, based on electromagnetic waves of various wavelengths, to measure temperature, turbulence, and heat propagation with fine spatial and temporal resolution.
