China's "Artificial Sun" experiment has new findings!
Recently, the physics experiment of China's "Artificial Sun" full superconducting tokamak nuclear fusion experimental device EAST, located on Hefei Science Island in Anhui Province, confirmed the existence of the tokamak density limit-free region based on the self-organized theory of boundary plasma and wall interaction. The related results were published in the international academic journal "Science Advances" on January 1, 2026.
For future fusion reactors, the fusion power is proportional to the square of the fuel density, so high-density operation is an inevitable choice to improve the economics of fusion energy. The "density limit" is a purely empirical scaling discovered at the end of the last century. Operating a tokamak near the density limit can cause plasma disruption, releasing a huge amount of energy to the device walls instantly, affecting the safe operation of the device. The international fusion community has refined cross-device empirical scalings and achieved super-density-limit operation under specific conditions such as central pellet injection, gradually clarifying that the physical process triggering the density limit occurs in the boundary region, but the underlying physical mechanisms are not yet fully understood.
In this work, the research team developed a boundary plasma and wall interaction self-organized (PWSO) theoretical model, pointing out the key role of boundary radiation in triggering the density limit, analyzing the radiative instability boundary; revealing the mechanism of triggering the density limit, predicting the density-free region beyond the density limit. Experimentally, relying on the EAST full-metal wall operating environment, methods such as electron cyclotron resonance heating and pre-gas injection were used to reduce boundary impurity sputtering, actively delaying the occurrence of the density limit and plasma disruption. By controlling the physical conditions of the target plate, the physical sputtering dominated by tungsten impurities on the target plate was reduced, allowing the plasma to break through the density limit and guide the plasma into a new density-free region. The experimental results highly coincided with the PWSO theoretical prediction, for the first time confirming the existence of the tokamak density-free region. This innovative work provides important clues for understanding the density limit and offers important physical basis for high-density operation of tokamaks.
(CCTV reporter Shuai Junquan, Chu Erjia)
Source: CCTV News Client
Original article: toutiao.com/article/1853181715112011/
Statement: The article represents the views of the author.