For four decades, nuclear fusion scientists have lived under the shadow of a figure: the Greenwald limit. Something that, in essence, is the “glass ceiling” of the reactors tokamak type and that supposedly prevents them from producing more energy than they could. But the one known as the China’s ‘artificial sun’ has broken this ceiling completely, and on top of it in a stable way (surpassing the European model).
The Greenwald Wall. To understand the achievement, you must first understand the problem. In a fusion reactorthe power you generate depends on the square of the density, this way, The more density there is inside the reactor, the more energy it will produce.. However, in 1989 the physicist Martin Greenwald formulated a rule that has remained unbeaten: there is a maximum density.
If this maximum density is exceeded, the plasma inside the reactor becomes unstable. What does this mean? Well, if this line is passed, the edge of the plasma cools down too much due to radiation, the electrical current contracts and the reactor suffers a disruptiona sudden stop that can even damage the reactor structure.
Bordering the limit. In this way, nuclear physicists have always been very attentive to this limitsince exceeding it can generate great chaos in a nuclear power plant. But logically what is always sought is to get the most out of all the resources available, which is why they have always been working very close to this limit, but never without exceeding it.
Until in the end it has been possible to overcome it and remove this limitation from the ‘speedometers’ of nuclear energy.
The study. The researchers They have achieved this fact, as they have reported in their article published in Science Advancewhere they point out that they have managed to achieve stable densities of between 1.3 and 1.65 times the Greenwald limit. It was not by brute force, but by experimental “finesse”. Something that they have been able to achieve within the Chinese Artificial Sun.
This means that the reactor has been able to work at 165% of its maximum theoretical capacity without suffering any disruption. It is as if we had discovered that an engine designed to go 200 km/h can travel at 330 km/h constantly and without overheating.
How has he achieved it? The key has not been just to “put in more gas”, but to change the way in which the Artificial Sun interacts with its own walls. Unlike other reactors, the Chinese Artificial Sun has tungsten on its walls, which is a metal that withstands heat better and makes the plasma less dirty.
In addition to this property of its walls, The researchers used high-power microwave waves to heat and “clean” the plasma just before ignition. This is in addition to the fact that they were able to validate a new theory that says that, under certain conditions, the plasma “organizes itself” to move away from the walls and remain stable, even if the density is extreme.
Real energy. What China’s Artificial Sun has shown is that the “density-free” regime is real. This changes the rules of the game for ITER (the large international reactor being built in France) and for the future CFETRthe reactor with which China hopes to begin pouring fusion energy into the electrical grid before 2040.
Its importance. With this new milestone, making giant reactors will no longer make sense, since with this new theory we no longer need gigantic machines to obtain the same energy. Furthermore, by operating in this new regime, the risk of plasma damaging the reactor is drastically reduced, since you will not be “playing” with the limit.
But the most relevant thing is that it has been seen that the denser the plasma is, the closer we are to “ignition”, the point where the Artificial Sun generates more energy than it consumes. This may mean that we are closer to the longed for infinite energy.
Images | Daniele La Rosa Messina POT
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