a reactor pushed to 100 million degrees for 30 seconds

The exploits of this South Korean tokamak will directly benefit ITER, the major nuclear fusion project based in France.

Korean physicists have just taken an important step for the future of work on nuclear fusion with their experimental reactor Korea Superconducting Tokamak Advanced Research center (KSTAR); for 30 seconds, he managed to maintain a temperature of 100 million degrees Celsius. Excellent news for ITER, the major international project based in France.

The KSTAR is not at its first attempt; since 2008, this reactor has served as an experimental platform to study the concepts that will one day be used to operate ITER. And this combination of very impressive figures represents a great progress.

This temperature, although close to 7 times greater than that of the Sun’s core, does not constitute a record in itself. Same thing for the 30 seconds of operation. But the fact of having succeeded in to achieve simultaneously is a great first, and a new step towards commercial nuclear fusion.

Don’t touch the wall

Very vulgarly, the objective of a tokamak, like EAST, KSTAR or ITER, is to force atoms carefully prepared in advance to collide at monstrous speed. To generate this vast nanometric 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; the engineers constantly seek to push back the limits of the various prototypes to reach the famous threshold of 150 million degrees Celsius. It is from this temperature (variable according to the machines) that the conditions become ideal at the threshold of the enclave, and that the fusion reaction can therefore begin within the plasma.

This furnace, no material in the world is capable of supporting it. To confine this superheated plasma, the tokamaks are equipped with gigantic electromagnets; they generate a magnetic field which keeps the ionized material at a good distance from the walls of the reactor.

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It’s very important for the stability of the reaction, and it’s not just about productivity. Admittedly, there is no risk of a Chernobyl-type disaster in this context; but if the plasma comes into contact with the internal 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 internal walls close to absolute zero, as stealthy as-it, immediately disrupts the system; this then triggers a snowball 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 field. The goal is to trap the plasma as efficiently as possible. It is a very important subject of study in this discipline; we remember, 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 bet on a modified version of a form of magnetic field called the Internal Transport Barrier. The peculiarity of this model is that it tends to make the plasma denser in the center of the reactor. On the other hand, it is more sparse on the periphery, near the walls.

They got a slightly lower density than they expected. Usually this is not good news. The energy produced by a reactor depends directly 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 by 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

Admittedly, 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 over a prolonged period. From now on, the challenge will be to learn how to push these tokamaks even further. This involves reaching even higher temperatures and above all longer confinement times, all without damaging the reactor.

And that’s just the tip of the nuclear fusion iceberg. There are plenty of other issues 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 larger-scale reactors.

And sooner or later, the issue of energy efficiency will also have to be addressed. Because as it stands, it is not even a question of recovering the energy produced by the reaction. This means that in addition to that which is used to heat the plasma and cool the enclave, any energy eventually produced by the reaction is also sacrificed on the altar of experimentation.

Suffice to say that even if this progress is impressive, we will have to be patient. Admittedly, the underlying physics are beginning to be well mastered. But there are now immense engineering challenges awaiting specialists at the turn.

The target temperatures and confinement times will probably not be reached before 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.

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