The Chinese nuclear fusion reactor has reached the density-free regime, with the plasma remaining stable even with increasing density.
China’s Experimental Advanced Superconducting Tokamak (EAST), often called the country’s “artificial sun,” has achieved a significant milestone in nuclear fusion research by maintain stable plasma at densities that exceed a threshold theoretical long-standing. Scientists say the breakthrough could help bring fusion energy closer to practical use, although commercial power generation is still years away.
According to a statement from the Chinese Academy of Sciences, EAST managed to maintain plasma, an extremely hot and electrically charged state of matter, at densities previously considered too unstable for sustained operation. The was published on January 1 in the journal Science Advances.
“The results suggest a practical and scalable path to extending density limits in next-generation tokamaks and fusion devices,” said Ping Zhu, professor at the University of Science and Technology of China and co-lead author of the study.
Nuclear fusion is widely seen as a potential source of clean energy practically unlimited. Unlike fossil fuels, nuclear fusion does not produce carbon emissions and, compared to nuclear fission, generates much less radioactive waste long-lasting. Fusion powers the Sun by forcing light atoms to combine into heavier atoms, releasing enormous amounts of energy in the process. Reproducing these conditions on Earth, however, has proven extremely challenging.
Fusion reactors need to heat the plasma to temperatures higher than the Sun’s core and confine it long enough for the atoms to collide and fuse. EAST is a tokamak, a donut-shaped magnetic confinement reactor designed to keep plasma stable for long periods. Although no tokamak has yet achieved fusion ignition, that is, a self-sustaining reaction, EAST has improved your performance constantly.
One of the main obstacles has been the Limite de Greenwalda density threshold beyond which plasma typically becomes unstable and stops fusion reactions. A higher plasma density is desirable because it increases the probability of atomic collisions and reduces the energy required for ignition.
According to , by carefully controlling the initial pressure of the fuel gas and the way in which electrons absorbed microwave heating, EAST researchers stabilized the plasma at densities between 1.3 and 1.65 times the Greenwald Limit. This is well above the reactor’s usual operating range.
Although other facilities have already surpassed the Greenwald Limit, including the DIII-D tokamak in the United States, the EAST experiment achieved a new regime known as “density-free regime“. In this state, the plasma remained stable even with increasing density, corroborating a theory called plasma-wall self-organization. The theory suggests that carefully balanced interactions between the plasma and the reactor walls can prevent instability.
This discovery is expected to contribute to future fusion projects, including the International Thermonuclear Experimental Reactor (ITER), under construction in France. ITER, a global collaboration involving China, the United States and other partners, aims to demonstrate sustained fusion reactions and is expected to begin full-scale operations in 2039.
