Chinese “artificial sun”the experimental tokamak EAST, became the first reactor in the world to operate stably in the so-called to the “density-free” regime, at plasma densities above the empirical Greenwald limit, which were long believed to automatically lead to reactor failure.
U to a new series of experiments scientists achieved in the “artificial Sun” that the average electron density reaches about 1.3 to 1.65 times the Greenwald limit, and that the plasma remains controlled, thus breaking one of the most stubborn “ceilings” in the history of fusion research.
The Greenwald limit is practically a “bumper” for the plasma density in tokamaks: when this threshold is crossed, the chances of instabilities and dangerous disruption events increase sharply, so all large reactors, including the Chinese “artificial Sun”, have had to operate below it until now. This meant that fusion projects sacrificed potentially higher energy output for the sake of safety and long, uninterrupted plasma operation.
The key to the breakthrough that pushed the Chinese “artificial Sun” into the “density-free” zone was to precisely control the initial pressure of the fuel gas from the start of the discharge and the additional heating of the plasma using electron-cyclotron resonance heating (ECRH).
Science DailyThis combination made it possible to optimize the interaction between plasma and metal walls (plasma-wall self-organization, PWSO), reducing the accumulation of impurities and radiative losses, so that the “artificial Sun” can raise the plasma density significantly above the old limit, without triggering an avalanche of instability.
The power of fusion reactions under standard deuterium-tritium conditions increases approximately with the square of the density, so the ability of the “artificial Sun” to safely exceed the Greenwald limit opens the door to tokamaks that can extract much higher output power from the same volume.
The scientists emphasize that the achieved “density-free” regime in the EAST reactor is not just an individual trick of the Chinese “artificial Sun”, but a practical scheme that can in principle be applied to future large-scale fusion reactors, including successors to ITER and commercial power plants.
The team working on the Chinese “artificial Sun” is already planning to test the same approach in high-performance plasma regimes, with stronger heating and parameters closer to those necessary for real fusion power plants, it writes. Science Daily.
If the “density-free” regime is confirmed in those, much “harder” conditions, future fusion reactors – the successors of today’s “artificial Sun” – could work stably in areas of density that until recently seemed like science fiction, making the scenario of a global network powered by fusion energy physically achievable for the first time within a human generation.