The exploits of this South Korean tokamak will directly benefit ITER, the large nuclear fusion project based in France.
Korean physicists have just taken an important step in the future of nuclear fusion work with their experimental reactor Korea Superconducting Tokamak Advanced Research Center (KSTAR); for 30 seconds it managed to maintain a temperature of 100 million degrees Celsius. Excellent news for ITER, the great international project based in France.
The KSTAR is not on its first attempt; since 2008 this reactor has served as an experimental platform to study the concepts that will one day be used to make ITER work. And this combination of very impressive figures represents great progress.
This temperature, although close to 7 times greater than that of the solar core, does not in itself constitute a record. Same thing for the 30 seconds of operation. But the fact of having succeeded reaching at the same time is an excellent first course, and a new step towards commercial nuclear fusion.
Don’t touch the wall
Very vulgarly, the goal of a tokamak, such as EAST, KSTAR, or ITER, is to force carefully prepared atoms in advance to collide at monstrous speed. To generate this vast nanoscale upheaval it is necessary to maintain an absolutely infernal temperature of several tens of millions of degrees.
However, generating such a temperature is not easy, far from it; engineers are constantly trying to push back the limits of various prototypes to reach the famous 150 million degrees Celsius mark. It is from this temperature (which varies according to the machines) that the conditions become ideal at the threshold of the enclave, and therefore the fusion reaction inside the plasma can begin.
this furnace, no material in the world can support it. To confine this superheated plasma, tokamaks are equipped with gigantic electromagnets; they generate a magnetic field that keeps the ionized material at a good distance from the reactor walls.
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It is very important for the stability of the reaction and it is not just about productivity. It is true that in this context there is no risk of a Chernobyl-type disaster; but if the plasma comes into contact with the inner walls of the reactor, it can still cause catastrophic damage inside this extremely expensive and very difficult to maintain device.
And at this level, researchers have no room for error. The smallest point of contact between the superheated plasma and the inner walls close to absolute zero, stealthy as-it immediately stops the system; this then triggers an avalanche effect that causes the reaction to fall like a soufflé.
A new form of magnetic field
To prevent this scenario, researchers are experimenting with different forms of magnetic fields. The goal is to trap the plasma as efficiently as possible. It is a very important subject of study in this discipline; we recall, for example, the work of DeepMind. The company specializing in artificial intelligence has gone so far as to develop an algorithm to optimize the shape of the magnetic field.
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To achieve this impressive combination of stability and temperature, KSTAR physicists relied on a modified version of a form of magnetic field called an internal transport barrier. The peculiarity of this model is that it tends to make the plasma in the center of the reactor denser. Instead, it is sparser on the outskirts, near the walls.
They have a slightly lower density than expected. This is usually not good news. The energy produced by a reactor directly depends on the temperature, density and confinement time of the plasma.
But in this case, the researchers explain that this modest density was not a problem. It was finally compensated by the temperature and the presence of very energetic ions in the center of the plasma. These play an important role in the stability of the reaction.
The road is still long
Of course, these figures are very impressive; but in absolute terms, the KSTAR and the other tokamaks are still far from being able to maintain the conditions necessary to maintain a fusion reaction for a prolonged period. From now on, the challenge will be learning how to push these tokamaks further. This involves reaching even higher temperatures and above all longer confinement times, all without damaging the reactor.
And this is just the tip of the iceberg of nuclear fusion. There are many other problems waiting for engineers around the corner. For example, for the moment, nothing indicates that the information provided by these experimental tokamaks will also be valid for large-scale reactors.
And sooner or later the issue of energy efficiency will also have to be addressed. Because as it is, it’s not even about recovering the energy produced by the reaction. This means that, in addition to that used to heat the plasma and cool the enclave, the energy produced by the reaction is also sacrificed on the altar of experimentation.
Suffice it to say that while this progress is impressive, we will have to be patient. Of course, the underlying physics are beginning to be well mastered. But now there are huge engineering challenges that await the specialists in turn.
Target temperatures and confinement times will likely not be reached until several years of iteration on these experimental tokamaks. JET, KSTAR and consorts will therefore continue to be essential players in nuclear fusion research for many years to come.