Revealing critical interactions between plasma turbulence scales improves fusion confinement

Revealing critical interactions between plasma turbulence scales improves fusion confinement
by Riko Seibo
Tokyo, Japan (SPX) Oct 23, 2025

Scientists have achieved a significant breakthrough in understanding fusion plasma confinement by identifying a new physical mechanism connecting turbulence at various scales. A research team led by Professor Tokihiko Tokuzawa and Project Professor Katsumi Ida at the National Institute for Fusion Science, with colleagues from the Graduate University for Advanced Studies and Kyoto University, developed specialized measurement instruments to observe multiple turbulence scales in the Large Helical Device (LHD).

Their experiments revealed that when turbulence at larger scales weakens, finer-scale turbulence grows stronger and becomes less deformed. This suggests that previously suppressed smaller eddies may expand, possibly explaining why performance improvements halt once a certain threshold is reached, despite the suppression of micro-scale turbulence. The observations confirmed theoretical predictions that smaller eddies are shaped and influenced by the electric fields originating from larger ones.

The cutting-edge millimeter-wave scattering system enabled simultaneous tracking of multiple turbulence directions and sizes within the plasma. These precise measurements illuminated how electric field distortions contribute to force flow and overall confinement dynamics. The researchers determined that cross-scale nonlinear interactions play an essential role; abrupt shifts in turbulence state can directly impact the efficiency of plasma containment.

The findings are especially relevant for next-generation fusion experiments like ITER, which depend on alpha particle-driven heating. The newly observed finer-scale turbulence is expected to become more influential as plasma conditions intensify and will affect future reactor designs and operational strategies. The group's experimental approach represents a world-first for capturing these elusive phenomena and verifying their underlying elongation processes.

Large-scale computer simulations also supported the possibility of cross-scale nonlinear interactions. The collaboration's achievements are expected to accelerate model development and performance improvements for fusion reactors worldwide. Beyond energy research, this advancement enriches understanding of turbulent interactions in cosmic plasmas, expanding the knowledge base across high-energy physics.

Research Report:Cross-scale nonlinear interaction and bifurcation in multi-scale turbulence of high-temperature plasmas