China's "Artificial Sun" Breaks Through Limits Previously Considered Impossible

China’s fusion reactor, known as the Experimental Advanced Superconducting Tokamak (EAST), has recorded a new achievement. The project, often nicknamed the “artificial sun,” can now operate plasma at density levels that have been considered difficult to achieve for decades. In its latest experiment, EAST successfully maintained plasma stability at 1.3 to 1.65 times beyond the Greenwald limit. This limit has long served as the primary reference for the safe threshold in tokamak reactor operations in various countries. In general, the tokamak in a fusion reactor works by trapping extremely high-temperature gas, or plasma, using magnetic fields. Under these conditions, atomic nuclei collide and produce fusion energy, the same type of energy that occurs in the Sun. For information, the most commonly researched fusion reaction is that the amount of energy produced increases proportionally to the square of the plasma density. In short, a slight increase in density can result in a large surge in energy. However, the problem is that plasma density that is too high also risks making the tokamak unstable. When this happens, reactor components can be damaged, leading to a sudden halt in operations. Therefore, the Greenwald limit was established as a safe guideline for tokamak reactors. Interestingly, EAST not only exceeded the Greenwald limit momentarily. The research team reported that the EAST plasma remained stable and controlled even when operated far above that limit. In its experiment, EAST used additional heating techniques from the initial plasma formation and carefully regulated the initial gas amount. EAST researchers also highlighted the importance of the relationship between plasma and the reactor wall. According to observations, plasma does not stand alone but always interacts with the surrounding surfaces. If this interaction is managed well, the plasma and walls can reach a relatively balanced condition. It is in this condition that the old density limit can be increased without immediately triggering major disruptions.