A domestic research team has uncovered the secrets of the 'multi-scale coupling' phenomenon, which has long been a challenge in plasma research. The study is evaluated to provide clues to solving academic challenges in plasma physics necessary for nuclear fusion technology development and cosmic origin research.
The Ministry of Science and ICT announced on the 7th that a joint research team from Seoul National University and the Asia-Pacific Center for Theoretical Physics has "proven the 'multi-scale coupling' phenomenon, one of the challenges in plasma physics, through fusion research of nuclear fusion experiments and cosmic plasma theory" in the international journal 'Nature'.
Plasma is a state where atomic nuclei and electrons exist separately in a high-temperature and high-pressure environment like the sun. It is also referred to as the 'fourth state' of matter, distinct from gas, liquid, and solid. In addition to being an intermediary of nuclear fusion reactions, it is a state of matter that occupies most of the universe.
The multi-scale coupling, which causes macroscopic changes through microscopic phenomena in such plasma, has been regarded as an important research topic because it can explain plasma changes, but it has been difficult to prove.
The research team conducted both experimental and theoretical studies through analysis of experimental data using a nuclear fusion experimental device and particle simulations conducted by the Korea Institute of Fusion Energy (KFE) using a supercomputer.
The research revealed that when micro magnetic turbulence occurs, the magnetic energy converts into plasma thermal energy, effectively generating 'magnetic reconnection' and leading to macroscopic structural changes.
The research team induced micro magnetic turbulence by injecting high-speed electron beams into two flux ropes, which are cylindrical magnetic structures created by the interaction of plasma with the magnetic field in the spherical toroidal nuclear fusion experimental device (VEST) established at Seoul National University.
Toroidal fusion is a method of confining plasma by applying a magnetic field inside a doughnut-shaped container, inducing nuclear fusion reactions. As the electron beams move at high speeds along the plasma, they create micro turbulence around the flux ropes, triggering magnetic reconnection, leading to the merging of the two flux ropes.
Since the research team confirmed that it is a phenomenon of multi-scale interactions that cannot be explained solely by existing magnetohydrodynamics (MHD), which progresses through the stages of micro magnetic turbulence generation, rope merging, equilibrium collapse, and reformation. They also proved that turbulence induced at the particle level causes magnetic reconnection and changes the magnetic structure of the entire system through simulations.
The research team stated that the significance of this research result lies in the fact that it is the first time a particle-level turbulence has been experimentally proven to change macroscopic equilibrium in the laboratory. They further noted that since it is similar to the magnetic reconnection energy spectra observed in actual cosmic plasma environments, it is expected that it can be applied to understanding fundamental physical phenomena.
Dr. Park Jong-yun of Seoul National University said, "The significance of this research result is that it was made possible through countless discussions and debates between experts in nuclear fusion and theoretical physics, starting from different interests, leading to a common conclusion," adding that "it provides new clues to the initiation of magnetic reconnection, which plays an important role even in cosmic environments like solar flares or magnetic storms."
Dr. Yoon Young-dae from the Asia-Pacific Center for Theoretical Physics said, "I hope this research achievement will contribute to expanding the framework for interpretation in the field of plasma physics as well as serve as a foundation for developing new nuclear fusion technologies."
References
Nature (2025), DOI: https://doi.org/10.1038/s41586-025-09345-9