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China has achieved a historic breakthrough in controlled nuclear fusion with the Experimental Advanced Superconducting Tokamak (EAST), known as the "artificial sun".
Researchers from the Plasma Physics Institute of the Chinese Academy of Sciences, Huazhong University of Science and Technology, and Aix Marseille University in France have surpassed the empirical plasma density limit, known as the Greenwald limit (n_G), reaching values between 1.3 and 1.65 times higher.
Historically, the plasma density in tokamaks has an upper limit: exceeding it causes the plasma to become unstable, escape magnetic confinement, and discharge energy onto the inner walls, causing disruptions and safety risks.
International research indicated that the phenomenon occurs in the plasma wall boundary region, but the precise mechanisms remained unclear.
The Chinese team developed a theoretical model of plasma. wall self organization (PWSO), revealing that radiative instability from impurities at the boundary (such as carbon and tungsten from the walls) triggers the limit.
By utilizing ECRH (electronic cyclotron heating) assistance and high gas pre filling pressure, they guided the plasma into a "density free zone," first experimentally confirmed in a tokamak.

During the plateau phase of the current (Ip ~250 kA, B_t=2.5 T), the average linear density reached 5.2-5.6 × 10^19 m^{-3}, reducing radiation, impurities (low Z_eff), and temperature at the divertor.
The results, published in Science Advances, agree with the PWSO 0D and 1D models, opening pathways for high density operations without disruption.
This advances towards the Lawson criterion for plasma burning and ignition, essential for clean and unlimited fusion energy.
The scalable technique promises applications on EAST and future reactors like ITER.
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