Energy record in nuclear fusion

The Joint European Torus generates 69 megajoules of energy from 0.2 milligrams of fuel - as much as is set free by burning two kilgrams of coal

At the Joint European Torus (Jet) in the UK, a European team has succeeded in releasing the largest amount of energy ever produced by a fusion experiment. The researchers, including scientists from the Max Planck Institute for Plasma Physics in Garching, generated 69 megajoules of energy from 0.2 milligrams of fuel. However, they needed even more energy to ignite the plasma than came out of the fusion process. A positive energy balance will only be possible with significantly larger fusion facilities such as Iter.

Fusion power plants are designed to fuse light atomic nuclei, following the example of the sun, in order to harness huge amounts of energy for humanity from very small amounts of fuel. The European research consortium Eurofusion is pursuing the concept of magnetic fusion, which is considered by experts to be the most advanced. With the large-scale experiments Asdex Upgrade and Wendelstein 7-X, the Max Planck Institute for Plasma Physics is driving forward research into this in Germany.

For experiments with the fuel of future power plants (deuterium and tritium), Europe's scientists operated the Jet research facility near Oxford together with the UK Atomic Energy Authority (UKAEA). A new world record was set there on 3 October 2023: 69 megajoules of fusion energy were released in the form of fast neutrons during a 5.2 second plasma discharge. 0.2 milligrams of fuel were required for this. The same amount of energy would have required about two kilograms of lignite – ten million times as much. Jet thus beat its own record from 2021 (59 megajoules in 5 seconds).

"This world record is actually a by-product. It was not actively planned, but we were hoping for it," explains Athina Kappatou, who worked for Jet as scientist of the Max Planck Institute for Plasma Physics. "This experimental campaign was mainly about achieving the different conditions necessary for a future power plant and thus testing realistic scenarios. One positive aspect, however, was that the experiments from two years ago could also be successfully reproduced and even surpassed." The latter was the case with the record-breaking experiment. The entire campaign is essential for the future operation of the international fusion plant Iter, which is currently being built in southern France, as well as for the planned European demonstration power plant Demo. Over 300 scientists and engineers from Eurofusion contributed to these landmark experiments.

The Jet record did not achieve a positive energy balance – in other words, more heating energy had to be invested in the plasma than fusion energy was generated. In fact, an "energy gain" is physically impossible with Jet and all other current magnetic fusion experiments worldwide. For a positive energy balance, these fusion plants must exceed a certain size, which will be the case with Iter.

The record-breaking experimentin the autumn was one of the last ever at Jet. After four decades the facility ceased operations at the end of 2023.