Berlin Nuclear fusion could become a pillar for a climate-friendly and sustainable energy supply. It supplies power regardless of the weather and takes up very little space – assuming it works.
There is still no proof of this, despite decades of research costing billions. But there are advances that indicate that the dreams of many physicists may yet come true.
Scientists from the “Joint European Torus” (Jet), a fusion experiment in Culham near Oxford, are now reporting on one of these successes. Accordingly, at the end of December, a stable plasma was generated from a mixture of the hydrogen isotopes deuterium and tritium, which released an energy of 59 megajoules. world record. Converted to the more manageable unit of power – energy per time – Jet achieved a good eleven megawatts over a period of five seconds.
In addition to the high fusion energy, it is these five seconds that are so important for the experts. “This shows that we can keep a high fusion power stable over a longer period of time,” says Athina Kappatou from the Max Planck Institute for Plasma Physics in Garching, who is involved in the experiments.
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Jet is the test facility for the Iter experimental reactor currently under construction in southern France. The plans for this were based on older experiments and many simulations, says the plasma researcher. “Our current results show that we are on the right track: we now have a better understanding of how to successfully run Iter.”
Tiles under neutron bombardment
As with all fusion systems, light atomic nuclei are to be fused into heavy ones, based on the model of the sun, and the energy released in the process is to be used. Jet shows how enormous the yield can be. There, less than 0.2 milligrams of a deuterium-tritium mixture was used and 59 megajoules were “taken out”. However, around three times as much energy had to be used beforehand to sufficiently heat up the plasma.
Only Iter can and should achieve a real surplus of energy. Jet is too small and designed too much as an experimental facility. For example, the magnets that hold the plasma in place are made of copper, which heats up. More than five seconds plasma discharge is technically not possible.
Rather, the researchers there want to find out how they can optimally heat the plasma and keep it stable using magnetic fields. It should not get too close to the wall of the beryllium and tungsten reactor vessel.
If this does happen, wall material must be prevented from flowing into the center of the plasma cloud. “Harming the plasma is more difficult the more fusion power is achieved and the longer the fusion takes place,” says Kappatou. So there is still a lot to do for you and your colleagues.
Another research topic is tritium production. The particularly heavy isotope of hydrogen is needed to mix it with deuterium to increase the yield of a future power plant.
Tritium is radioactive and decays rapidly, so it does not occur naturally. So far it has been produced in nuclear fission reactors. In the future, fusion reactors will breed it themselves using the neutrons that are released. These meet lithium in the wall tiles, where the desired tritium is formed.
The energy of the neutrons is also absorbed in the tiles: the fast particles are slowed down in the material, which heats up in this way. This thermal energy is then transported by a coolant through a heat exchanger to the turbine and generator, where the thermal energy is converted into electrical energy.
The neutrons also react with the other materials in the reactor. Here it is important to find mixtures that survive and withstand the bombardment. Another problem: the neutrons can produce radioactive substances in the vessel wall. Here, too, it is important to find a favorable combination of materials so that little radioactive waste is produced, the radiation from which decays quickly.
How quickly Iter will be operational is – once again – an open question. The official target date is 2025, but there are signs of delays again. Even if the reactor produces more energy than it consumes, it remains a research device. Only the successor called Demo should feed electricity into the grid, starting around the 2050s.
Raised billions in venture capital
It could go faster with electricity from fusion power plants. At least that’s what a number of start-ups who want to use core fusion with a wide variety of technologies to their advantage claim.
One option is to use powerful laser pulses to compress matter so tightly that the reaction starts. This concept received a boost when the National Ignition Facility in Livermoore, California, recently released new data.
According to this, it was possible to gain up to 1.35 megajoules of fusion energy, which corresponds to around 70 percent of the laser energy previously used. However, the losses in the massive laser system had already been factored out. We are also very far away from the continuous operation that a power plant needs.
The situation is similar with the other ideas. Karl Lackner, senior fusion researcher at IPP for many years and coordinator of the European contributions to Iter, took a closer look at the different concepts.
“A lot of them are serious and have great solutions to specific problems,” he says. But that doesn’t mean that the system works well in the end. “The further you get in technological development, the bigger the machines become and you are technologically much more limited, you can’t vary much anymore.”
Ambitious timetables to bring electricity to the grid as early as the early 2030s should therefore be viewed with skepticism. That doesn’t deter investors, however.
Taken together, the young industry has already raised billions in venture capital. German companies are also involved. The Munich technology developer Marvel Fusion reported a few days ago that it had received 35 million euros from investors. The team is working on a laser-based nuclear fusion and, according to the announcement, is cooperating with Siemens Energy and the laser specialist Trumpf, among others.
This article first appeared in the Tagesspiegel.
More: Siemens Energy, Trumpf and Thales: Fusion start-up Marvel Fusion is getting reinforcements