Generate energy like our sun: The largest amount of energy to date has been achieved from a fusion experiment at a European nuclear fusion research facility in Great Britain.
Replicating the energy source of the stars on Earth – that is the goal of research on nuclear fusion reactors. When hydrogen nuclei fuse inside the sun, enormous amounts of energy are obviously released. A replica of this legendary energy source on Earth would also produce only a small amount of weakly radioactive waste.
And the fusion reaction taking place inside it would stop on its own in the event of the slightest disturbance – a catastrophic build-up to the point of a worst-case scenario, as in a conventional nuclear power plant, in which atomic nuclei are split and not fused, is not possible in the fusion reactor. But the technical requirements for a fusion reaction are complex.
World record in the last experiment
A first power plant could perhaps be built in decades. The reactors now in operation are all used solely to research the technical fundamentals. One of these reactors, JET (Joint European Torus), has been located in Culham in Great Britain since 1983.
After 40 years, the research facility, in which several European countries are involved, was decommissioned in autumn 2023 – but before that it was technically exhausted to the limit. This is how another world record was achieved in October 2023 – which the EuroFUSION research association has now announced in February 2024. An amount of energy of 69 megajoules was released by fusing hydrogen isotopes.
So far the energy balance has been sobering
69 megajoules of energy are enough to bring the water in three well-filled bathtubs to wellness temperature. However, with the total energy used to operate the JET reactor, more than 100 bathtubs could have been heated.
To build a power plant you would have to be able to reverse this ratio of energy expenditure to energy gain. This would be possible if the mixture of atomic nuclei and electrons contained in the reactor – the plasma – could be ignited.
Ignition: This is the point at which the fusion reaction can sustain itself because it releases so much energy that the plasma remains millions of degrees hot and, in addition, a power plant can be operated with excess heat.
Plasma ignition not a breakthrough in the USA
After all, the first successful plasma ignition has already been reported in the USA in November 2022. At the Lawrence Livermore National Laboratory in the USA, a tiny sample of frozen hydrogen was bombarded with powerful lasers. Under the sudden onset of heat, the atomic nuclei fused and energy was released – actually more than the laser shot in. 2.05 megajoules became 3.15 megajoules.
However, the balance did not take into account the fact that the production of the laser radiation also required energy – if you take that into account, the balance of the Livermore experiment also becomes negative. In addition, the plasma can only be ignited in this way for a fraction of a second – then the fuel is already used up.
There are still no technical concepts for building a reactor in continuous operation. This approach is therefore suitable for researching ignited plasmas, but not for building reactors. This is different with JET and the experimental reactor ITER (International Thermonuclear Experimental Reactor) currently under construction in southern France.
Energy production modeled on the sun
In the JET nuclear fusion reactor, very thin gas is heated in a 4.2 meter high and 2.5 meter wide tube closed to form a ring. At high temperatures, atomic nuclei and the atomic shell, which consists of electrons, separate from each other. A plasma is created and the shellless atomic nuclei collide so violently that they fuse with each other and energy is released – in the form of heat.
A similar process occurs in the sun. Since there is very high pressure inside the sun, 15 million degrees is enough to force the atomic nuclei to fuse. Such high pressure cannot be achieved in fusion reactors on Earth. Instead, the plasma trapped within them must be heated to over 100 million degrees to reach the threshold for nuclear fusion. This super-hot plasma must not touch the reactor walls – not only because it could cause heat damage, but because the plasma would immediately cool down upon contact with the walls and the laboriously started fusion reaction would collapse.
The situation is similar to a hot water bottle placed on an iceberg. It cannot melt the iceberg, which weighs several tons, but instead cools down and freezes itself. Likewise, the massive, multi-ton reactor walls would instantly cool down the thin plasma cloud floating in space, which weighs just a tenth of a gram. Super-strong magnetic fields therefore prevent the plasma cloud from touching the reactor walls.
Technical challenges to produce nuclear fusion
The technically necessary strong magnetic fields can only be produced economically using superconductors – materials that conduct electrical current without any resistance, but which require complex cooling to do so.
The preferred design for fusion reactors so far is the so-called tokamak. However, it brings with it a major technical challenge: In order for the plasma cloud in the tokamak to remain compact, an electrical current must flow inside it. This plasma current is excited by a magnetic field.
In order to create this magnetic field, a constantly increasing electrical current must flow around the reactor vessel. Since the current cannot increase to infinity, the tokamak must be switched off and cooled down occasionally. These cycles put enormous strain on the machine.
The opposite concept to the tokamak is the stellarator. It works without the plasma current. The calculation of the magnetic fields required in it is so complicated that it could not be carried out for a long time. But this became possible with high-performance computers and the stellarator, which many people thought was on the sidelines, is once again a concept with a future. In the future, technical elements of the tokamak will probably be installed in the stellarator and vice versa – the technical differences between the two concepts could become blurred.
First power plant not before 2050
JET’s successor is ITER – which stands for International Thermonuclear Experimental Reactor – a fusion reactor that is currently being built in southern France. 35 countries are involved in this project. Development of the site began in 2007. After many delays, ITER is scheduled to go into operation in 2025. Tests will then be carried out there, in the course of which an ignition of the plasma that lasts several minutes will ultimately be achieved in the 1930s.
If things run optimally, ITER could produce roughly as much energy as the operation of the facility consumes. But only the successor to ITER, called DEMO (DEMOnstration Power Plant), would be the first experimental fusion power plant that would be capable of a net gain in the energy balance and could feed 300 to 500 megawatts into the power grid. However, DEMO will not start operations before 2050.
Uwe Gradwohl, SWR, tagesschau, February 8, 2024 2:28 p.m