Major scientific breakthroughs sometimes hide a mountain of difficulties to come. So much so that it is not always easy to assess its scope. As such, the latest results from the National Ignition Facility (NIF) in Livermore, California, should be viewed with some distance.
Its researchers have in recent days taken a new step on the way to nuclear fusion, this physical reaction inspired by stars. For the first time, they recovered 20% more energy than they injected into their experiment. They also got a start of a self-sustaining reaction. “We cannot underestimate the significance of the event. We have been chasing this kind of result for seventy years. From a scientific point of view, it is extremely interesting”, assures Greg de Temmerman, doctor in experimental physics and general director of the think tank Zenon research.
But paradoxically, the progress of the NIF does not fundamentally change the situation with regard to the final objective of the researchers: to develop a fusion reactor capable of producing electricity for the country. “In the United States, scientists are more dependent on the progress made to obtain funds. They therefore undoubtedly have an interest in communicating” advances Guy Laval, physicist, director of research emeritus at the CNRS and member of the Academy of Sciences. But in reality, nuclear fusion still poses just as many problems for them.
The NIF uses a so-called “indirect” approach: its lasers do not directly strike a fuel but a small metallic gold cell. “When it implodes, it generates X-rays which will heat the fuel,” explains Greg de Temmerman. The problem? 70 to 80% of the energy used is lost in the operation. Important losses also occur during the loading of the lasers. “If we look at the whole chain, the yield becomes very small”, observes Guy Laval. And even if we focus on the final shot, performance of 20% remains largely insufficient to consider one day a commercial application.
“The targets currently used by the Americans are extremely complex. And their high cost remains well above the price of the energy that will be extracted from them”, specifies the physicist. “As things stand, we cannot industrialize such a system, confirms Greg de Temmerman. Imagine a very small cryogenic ball at – 250 degrees, pressed in a gold vice and lasers firing on it twenty times per second without any margin of error because if you deviate by a few microns, you lose a lot of performance. Technically, it’s really complicated.”
Iter outdated?
According to specialists, future reactors will therefore have to be based on so-called “direct” approaches, therefore without the famous capsule. But no one really knows what they might look like. “There are many projects in this field of research but they had been shelved precisely because there were not very stimulating results. The announcements of the NIF could recreate a momentum”, comments Guy Laval.
What make the international Iter project outdated, which is also trying to obtain fusion but by betting on magnetic confinement? “Laser technologies are progressing rapidly. They are no longer reserved, as in the past, for military applications. Research on inertial fusion (using lasers) began much later than those based on magnetic confinement. And yet this they are the ones who have just obtained a 20% energy gain”, observes Greg de Temmerman.
On paper, the project carried out in the south of France still has an advantage: “If Iter achieves its objectives, we can immediately move on to the next stage, which is the specific and technical study of an electricity-producing reactor. So with this initiative, we are really in a stage of preparation for the sequel, unlike techniques using lasers”, explains Guy Laval. But the construction still needs to move forward. For now, the delays continue to accumulate and the costs to swell. In the absence of an outbreak of fever in the reactor, this bad news could well end up scalding the founding member countries of the project.