Nuclear Fusion: A reactor pushed to 100 million degrees for 30 seconds


The exploits of this South Korean tokamak will directly benefit ITER, the main nuclear fusion project based in France. Korean physicists have just taken an important step for 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 large international project based in France. The KSTAR is not on its first try; since 2008, this reactor serves as an experimental platform to study the concepts that will one day be used to make ITER work. And this combination of very impressive numbers represents great progress. This temperature, although almost 7 times higher than that of the Sun’s core, does not constitute a record in itself. The same for the 30 seconds of operation. But the fact that they have been achieved simultaneously is a great first, and a new step towards commercial nuclear fusion. Don’t touch the wall Put simply, the purpose of a tokamak, such as EAST, KSTAR or ITER, is to force carefully prepared atoms to collide at monstrous speeds. To generate this great nanometric disorder, it is necessary to maintain an absolutely hellish temperature of several tens of millions of degrees. However, generating this temperature is not easy, far from it; 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 depending on the machines) that the conditions become ideal at the threshold of entrapment and therefore the fusion reaction can begin within the plasma. This furnace, no material in the world is able to withstand 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. Nuclear Fusion: When Will We Have Our Artificial Sun? It’s very important for the stability of the reaction, and it’s 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 margin for error. The slightest point of contact between the superheated plasma and the near-absolute-zero internal walls, however stealthy, 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 avoid 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; let’s remember, for example, the work of DeepMind. The company specializing in artificial intelligence has developed an algorithm to optimize the shape of the magnetic field. DeepMind taught an AI to control nuclear fusion To achieve this impressive combination of stability and temperature, KSTAR physicists relied on a modified version of a form of magnetic field called the Internal Transport Barrier. The particularity of this model is that it tends to make the plasma denser in the center of the reactor. On the other hand, it is scarcer on the periphery, near the walls. They got a slightly lower density than they expected. In general, this is not good news. The energy produced by a reactor is directly dependent 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. Finally it was 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. There is still a long way to go. It is true that these figures are very impressive; but in absolute terms, KSTAR and the other tokamaks are still far from being able to maintain the conditions necessary to sustain a fusion reaction for an extended period. From now on, the challenge will be to learn how to push these tokamaks even further. This implies 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 still many other problems that the engineers will have to solve. For example, at the moment there is no indication that the information provided by these experimental tokamaks is also 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’s not even about recovering the energy produced by the reaction. This means that in addition to what is used to heat the plasma and cool the enclave, any energy possibly produced by the reaction is also sacrificed at the altar of experimentation. Suffice it to say that while this progress is impressive, we will have to be patient. It is true that the underlying physics is starting to take hold. But now there are immense engineering challenges waiting for specialists to turn. The target temperatures and confinement times will probably not be reached before several years of iteration in these experimental tokamaks. Therefore, JET, KSTAR and consorts will continue to be essential players in nuclear fusion research for many years to come.
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