The Experimental Advanced Superconducting Tokamak is a nuclear-fusion research reactor in Hefei, China.Credit: Zhang Yazi/China News Service/VCG via Getty
Researchers working on China’s ‘artificial sun’ have reported breaking a long-accepted threshold that has limited the operation of nuclear-fusion reactors for decades.
China’s Experimental Advanced Superconducting Tokamak (EAST) is a nuclear-fusion research reactor in Hefei. Researchers hope that it will one day produce clean, nearly limitless energy by replicating the fusion processes that power the Sun.
In fusion reactors, light-weight atoms are compressed under extreme pressure and heat to form heavier atoms. This process releases energy, but it must be optimized carefully so that the reactor produces more energy than it consumes.
One of the most promising reactor designs, the tokamak, confines plasma inside a doughnut-shaped chamber using magnetic fields. The plasma is then heated. To sustain fusion reactions, the plasma must reach an extremely high density — meaning many particles must be packed into a small volume.
But researchers thought that plasma could not exceed a certain density without becoming unstable. This upper limit — known as the Greenwald limit — has been a major obstacle for fusion research, particularly for tokamak-type devices.
In a paper published on 1 January in Science Advances1, scientists working on China’s EAST device reported pushing plasma densities beyond this limit, achieving densities 30% to 65% higher than those normally reached by EAST.
“These results are very promising and should be explored in other tokamak devices,” says Jeronimo Olaya, a fusion plasma physicist at the French Alternative Energies and Atomic Energy Commission in Saint-Paul-lez-Durance.
Fewer impurities
In 2021, study co-author Dominique Escande, a plasma physicist at the Aix-Marseille University in France, and colleagues first proposed2 that the Greenwald limit could be surpassed by adjusting the conditions so that the plasma and the inner wall of the reactor are in a stable, mutually reinforcing state.
... continue reading