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A clue for a fusion conundrum: Defining the interaction between magnetic islands and plasma turbulence


Date of registration 2021-04-23


(Photo: Dr. Minjun J Choi and his article in Nature Communications)

Dr. Minjun J Choi of the KSTAR Research Center of KFE has successfully proven the direct effects of plasma turbulence on magnetic islands. The findings, from a collaborative investigation involving researchers from Korea and the United States, were published in Nature Communications in January.

“This research is the reverse of a previous study that revealed the effect of magnetic islands on the distribution and development of background turbulence. This time, we analyzed how background turbulence affects the evolution of magnetic islands. Based on this work, we expect to be able to weaken or redistribute the turbulence near magnetic islands, to prevent or alleviate plasma disruption," explained Dr. Choi, who was first author of the paper.

A magnetic island is an island-like magnetic structure that is created in a plasma by a magnetic field reconnection, due to plasma instabilities. It can degrade tokamak performance by interfering with its magnetic confinement or can even cause plasma disruption. Understanding its effect and behavior has been one of the most difficult conundrums to solve in fusion research, and doing so is essential to realizing fusion energy.

Several projects were being carried out on multiple fusion devices to address the problem. Dr. Choi focused his efforts on the interactions between magnetic islands and background plasma turbulence. The collaborative research team successfully proved by experiments on KSTAR that turbulence directly influenced magnetic islands to evolve by turbulence spreading or magnetic reconnection acceleration. Contributing researchers include Dr. Laszlo Bardoczi (General Atomics, US), Dr. George McKee (General Atomics, US), Professor T. S. Hahm (SNU, Korea), Professor Hyeon K. Park (UNIST, Korea), Professor Eisung Yoon (UNIST, Korea), and Professor Gunsu S. Yun (POSTECH, Korea).

Multiple physics models have emerged to explain how plasma turbulence affects the evolution of magnetic islands, though few have been supported by actual experiments. Recent studies have suspected that turbulence spreading was suppressing the magnetic islands, but verifying it experimentally was difficult. The advanced diagnostics of KSTAR allowed the team to observe the turbulence as it spread from the outside of the magnetic islands to the inside. They were also able to witness turbulence enhancement at the reconnection site in the event of a fast collapse of a magnetic island.

The findings provide a solid explanation of the main plasma phenomena necessary to realize fusion power. The researchers expect to contribute to future fusion reactor operations by advising how to suppress the magnetic islands causing plasma disruption.

Related publication: Effects of plasma turbulence on the nonlinear evolution of magnetic island in tokamak

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