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Researchers working on the Experimental Advanced Superconducting Tokamak, a nuclear fusion reactor developed by the Chinese Academy of Sciences, have discovered a way to increase the density of fusion plasma beyond traditional limits, bringing us closer to the goal of creating a “man-made sun.”
This breakthrough offers fresh insights into overcoming one of the most challenging physical barriers on the road to achieving nuclear fusion ignition. The study was led by experts from Huazhong University of Science and Technology and the Hefei Institutes of Physical Science of the Chinese Academy of Sciences, and was published in Science Advances on January 1.
The team managed to reach a theorized “density-free regime” for fusion plasma by implementing a new high-density operational scheme on the tokamak device located in Hefei, in eastern Anhui Province. Their work demonstrated that plasma density can be significantly increased without causing disruptive instabilities.
Nuclear fusion is widely seen as a highly promising source of clean, sustainable energy. Yet, in conventional tokamak operations, plasma density is limited by an empirical ceiling. Going beyond this limit often triggers instabilities that threaten to disrupt plasma confinement and compromise the operation of the device—posing a major obstacle to advancing fusion technology.
Recent developments in plasma-wall self-organization theory have provided a new perspective on understanding the disruptive density limit. This theory suggests that a novel density-free state could be achieved if a careful balance is maintained between the plasma and the metallic walls of the reactor.
To reach this state, the experiments combined control of the initial fuel gas pressure with electron cyclotron resonance heating during startup. This strategy allowed for effective optimization of plasma-wall interactions from the very beginning of the discharge.
As a result, interactions between the plasma and the wall, impurity buildup, and energy losses were significantly minimized, enabling plasma to attain much higher densities.
“This discovery points to a practical and scalable method for pushing the density boundaries in tokamaks and future burning plasma fusion devices,” said Zhu.
The research team plans to test this new approach during high-confinement operation phases on the EAST device in the near future, aiming to access the density-free regime under conditions of high-performance plasma, according to Yan.
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