Scientists working with China's Experimental Advanced Superconducting Tokamak (EAST) have succeeded in reaching a state long predicted by theorists, known as the "density-free regime."
Scientists working with China’s Experimental Advanced Superconducting Tokamak (EAST) have achieved a state long predicted by theorists, known as the “density-free regime.” In this regime, the fusion plasma remains stable even at densities far above the limits of tokamak experiments, without degenerating into the violent instabilities that usually shut down the operation. The achievement marks an important step toward solving one of the great physical challenges in fusion energy. The findings were published in the journal Science Advances on January 1, 2026.
How do you push the density without “breaking” the tokamak?
The research was jointly led by Professor Ping Zhu of Huazhong University of Science and Technology and Associate Professor Ning Yan of Hefei Institutes of Physical Science Chinese Academy of Sciences. Using a new high-density operation approach developed for EAST, the researchers showed that the plasma density can be pushed far beyond the empirical limits that have been accepted for years, without inducing the severe instability that usually “turns off” tokamak experiments.
Why is plasma density critical to fusion performance?
Nuclear fusion is seen as a possible way to produce clean and reliable energy. In deuterium–tritium fusion, the fuel must be heated to about 13 kiloelectronvolts (keV), or about 150 million Kelvin, to reach an optimal reaction rate. At such extreme temperatures, the power obtained from fusion increases in proportion to the square of the plasma density. However, for decades, tokamak experiments have been limited by a “density ceiling”: crossing this limit usually leads to disruptions that damage plasma confinement and threaten the stability of the facility—and therefore make it very difficult to achieve higher fusion performance.
"“Wall-Plasma Self-Organization”: The Theoretical Framework and Experimental Verification
A newer theoretical framework, plasma-wall self-organization (PWSO), offers another way to understand density limitations. The idea was first proposed by D.F. Escande and colleagues at the French National Center for Scientific Research (CNRS) and Aix-Marseille University. According to the theory, a density-free regime becomes possible when the plasma and the metal walls of the reactor reach a delicate equilibrium, especially in systems where the plasma-wall interaction is dominated mainly by physical sputtering.
The EAST experiments provided the first experimental confirmation of this idea. The researchers carefully controlled the fuel gas pressure at the beginning of the process, and applied electron cyclotron resonance (ECRH) heating at the very start of each plasma discharge. This early control helped to “tune” the plasma-wall interactions from the very beginning. As a result, impurity accumulation and energy losses were significantly reduced, and the plasma density could gradually increase until the end of the start-up phase. Under these conditions, EAST successfully entered the density-free regime predicted by PWSO theory, and maintained stable operation even at densities well above the conventional limits.
Meaning: A practical path to approaching ignition
The results provide new insights into how the long-standing “density barrier” in tokamak operation can be circumvented, on the way to fusion ignition.
“The findings point to a practical and scalable path to extending the density limits in tokamaks and next-generation fusion facilities, where the plasma ‘burns,’” said Prof. Zhu.
Prof. Hever Yan added that the team plans to apply the same method during high-confinement operation at EAST in the near future, with the goal of achieving a density-free regime even under higher-performance plasma conditions.
More of the topic in Hayadan:
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Can't you at least fix the machine translation errors?
I hope they succeed and free the Earth from greenhouse gases and carbon dioxide. May it be in our lifetime.
In my humble opinion, adding excess matter could lead to the creation of conditions for a black hole that will suck in everything around it.
It seems to me that they are literally "playing with fire".!!!