Power generation: Fusion of the nuclei

In recent decades, nuclear fusion has been dismissed by many as science fiction. Scientists often joke that one constant in nuclear physics is that the use of nuclear fusion to generate electricity is always 30 years away. Unlike in the past, however, there could be some truth in the prediction today. That is because nuclear fusion research has recently been attracting attention with some striking findings. Reason enough to take a closer look at this technology, which, unlike nuclear fission, does not produce radioactive waste with a half-life of several thousand years. The best way to understand the physical processes is to look at the Sun, where hydrogen atoms are constantly colliding with such force that they combine and release energy in the form of light and heat. But how can we recreate the solar model on earth? This is anything but easy, because it takes a huge amount of energy to make subatomic particles collide and fuse together – especially as atomic nuclei are positively charged and repel each other. Bringing them together is only possible with extremely high temperatures of 15 million degrees Celsius, a pressure of 100 billion bar and a corresponding particle density.

In the Sun, hydrogen atoms constantly collide with such force that they combine and release enormous amounts of energy. How can you recreate this model on earth?

That's why, having begun researching nuclear fusion in the 1950s, researchers did not succeed until two years ago in producing a nuclear fusion reaction that generates more energy than it consumes. The achievement came on December 5, 2022, when researchers at the National Ignition Facility (NIF) at the Lawrence Livermore National Laboratory (LLNL) in California generated a net energy gain of more than 50 percent – an absolute first and a sensation in the science community. The world’s most powerful laser system was used to heat the inside of a container just a few millimeters in size. The inner walls of the container emitted high-energy X-rays and heated a hydrogen-filled fuel capsule inside the container. The intense pressure and extremely high temperatures in the fuel led to the fusion of deuterium and tritium nuclei to form helium nuclei. Through the so-called ignition of the fuel plasma, the temperature could be maintained without external heating, and a self-sustaining continuous reaction was achieved.

Prof. Markus Roth, Professor of Laser and Plasma Physics at TU Darmstadt, followed the experiment closely. He not only conducts basic experimental research into the interaction of intense laser beams with matter, but is also co-founder and scientific director of the spin-off start-up Focused Energy. The German-American company maintains close ties with researchers in the Bay Area and also uses laser-based technology. “The success of our colleagues is fantastic because it shows that the plasma can be ignited if the right conditions are achieved,” says Roth. “The physical process is stable, but 99 percent of the energy is still lost. The task now is to optimize the engineering aspects and increase efficiency.” While Focused Energy is following the same approach to the final phase of ignition and burning of the plasma, in other respects the company is using methods of its own. The plan is to use more modern lasers equipped with high-performance lenses that provide significantly higher efficiency and greater accuracy. Moreover, the fuel capsule is to be irradiated directly rather than indirectly.

In addition to the relatively new laser technology, there are other approaches to fusion, such as mechanical or magnetic compression of the plasma. Work on magnetic fusion has been going on for some time, and a major success was recently achieved: in cooperation with the Max Planck Institute for Plasma Physics, the Joint European Torus (JET) facility in Culham, UK, was able to generate 69 megajoules of energy from 0.2 milligrams of fuel. It would have taken around 2 kilograms of lignite (around ten million times as much fuel) to produce the same amount of energy. In magnetic fusion, the fuel – i.e. fusion plasma consisting of the two isotopes – is compressed together by an extremely strong magnetic field in a large, donut-shaped vacuum chamber. This heats it up until ignition. The magnets ensure that the plasma created during heating is kept in the center of a circular path and does not hit the walls of the container, which would be unable to withstand the high temperatures caused by induced current, radio waves and high-energy particles.

It is not only researchers and industry representatives who are optimistic about fusion research. Private investors have already invested several billion euros.

Magnetic fusion is also being tested in Greifswald, Germany. Here, the Max Planck Institute for Plasma Physics operates Wendelstein 7-X, the world’s largest stellarator-type fusion facility. Compared with the tokamak reactor chamber in Culham, the stellarator works with a differently shaped magnetic field. In September 2024, around 150 plasma experts from some 30 nations started the fourth operating phase here. Now the machine is to be pushed to its performance limit, generating plasma that has a temperature of up to 40 million degrees Celsius, is significantly denser and also remains stable for longer. For this purpose, a six-million-euro plasma injector was installed – a type of injection nozzle through which small frozen hydrogen globules are blown into the plasma to increase its density.