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JET research reactor in Great Britain

Photo: CEA-IRFM / EUROfusion / ZUMA Wire / IMAGO

A “world record” is said to have been achieved: this was announced by the Max Planck Institute for Plasma Physics (IPP). What this means is that researchers at the Joint European Torus (JET) nuclear fusion facility in Great Britain have obtained the largest amount of energy ever achieved in a fusion experiment, the institute writes. In numbers: 69 megajoules of energy were produced from 0.2 milligrams of fuel.

A television could run for several hours, as could a kettle or an electric stove.

Fusing atomic nuclei could be an efficient, safe and environmentally friendly source of energy. It would be a tool in the fight against the climate crisis, which is also why politicians and scientists have a lot of hope in the method. The goal: to make nuclear fusion usable as a mass-produced energy source.

Atomic nuclei are full of energy, but it is tightly sealed inside. There are two ways to release them: by splitting heavy atomic nuclei, as happens in conventional nuclear power plants, or by fusing light nuclei, i.e. fusion. Unlike after nuclear fission, the radioactivity of waste from nuclear fusion decreases quickly, and the risk of reactor accidents is also considered minimal.

At least that's the theory. Although research is making progress, large-scale use of nuclear fusion is still a long way off.

Atomic nuclei are positively charged. Bringing them together is not easy because their charge causes them to repel each other like the positive poles of two magnets. In order to achieve fusion, extremely high temperatures and a high particle density are required. There are two ways to do this. A tiny vessel in which the fusion is to take place is irradiated with lasers, heating it to several million degrees Celsius. Or magnets are used, as in the case of JET.

“Scientifically speaking, this is a wonderful result”

In magnetic fusion, a fuel is trapped by an extremely strong magnetic field in a shape that can be imagined as a donut. The magnets keep the atomic nuclei in a circular path and do not hit the outer walls. The heat does not come from a laser, but is produced by induced current, radio waves and high-energy particles.

The hydrogen isotopes deuterium and tritium are generally used as fuel. In JET, these hydrogen isotopes are heated into an extremely hot plasma. Plasma is a wild mixture of particles in which atomic nuclei are decoupled from the electrons that actually surround them. The components – the positively charged nuclei and the negatively charged electrons – are present separately from each other. The charge plays an important role in fusion: Because like charges repel each other, the plasma can only be kept in suspension by a very strong magnetic field in the ring-shaped reactor.

A high density is also important for fusion: a deuterium nucleus and a tritium nucleus collide and fuse to form a helium nucleus. This releases energy, which can then be converted into electricity.

Not pure energy gain

How much electricity comes out also depends on the time the plasma burns. In the experiment it was 5.2 seconds. Two years ago, an experiment at the research reactor reached 59 megajoules – in five seconds. “So you have a much better understanding of how to contain and control the plasma,” says Markus Roth, professor of plasma and laser physics at TU Darmstadt, to SPIEGEL. “Scientifically speaking, this is a wonderful result.”

However, the experiment was initially unable to solve a major problem with nuclear fusion: it remains a loss-making business. In order to gain some energy, a multiple of it was previously put into the process.

At the end of 2022, a research group at the National Ignition Facility (NIF), a research facility at the Lawrence Livermore National Laboratory in California, succeeded in an experiment in obtaining more energy from nuclear fusion than had previously flowed into the process. At least if you ignore the power consumption of the technology. "Simply put, this is one of the most impressive scientific achievements of the 21st century," said US Secretary of Energy Jennifer Granholm when presenting the research.

NIF uses laser fusion. The Max Planck Institute writes that it is currently not physically possible to achieve energy gain with experiments on magnetic fusion. In order to achieve a positive energy balance, these fusion systems must exceed a certain size, which JET simply does not have. “But that doesn’t detract from the result,” says Roth, “but is another small step towards a fusion reactor suitable for mass production.”

A successor project to JET is currently being worked on in southern France: ITER (International Thermonuclear Experimental Reactor). It aims to demonstrate the scientific and technological feasibility of fusion energy. But this research reactor is not about a positive energy balance; it is only about the next successor. “But it still has to be designed and built,” says Roth.

Roth does not expect a demonstration power plant that could be able to produce electricity for the first time until the end of the 1930s at the earliest. Hourly first, there is still a lot to explore. For example, how the power plant actually works over a long period of time. And: very theoretical, because the starting point for ITER has already been postponed several times. “The earliest we could get the first fusion power plants online at marketable prices would be the mid-1940s,” says Roth.

On October 3, 2023, the researchers at JET achieved success. “Actually a byproduct,” said Athina Kappatou from the IPP. »This experimental campaign was mainly about achieving the various conditions necessary for a future power plant and thus testing realistic scenarios.«

The experiment was one of the last ever to be carried out in JET. After four decades of operation, the research reactor was shut down at the end of last year. “Shortly before the end, our colleagues stepped up their game again,” says Roth, “that’s a wonderful conclusion.”

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