The world lives on fossil fuels, but the ever-present specter of climate change has spurred research into cleaner forms of energy such as wind and solar. For decades, scientists have been working on nuclear fusion to produce unlimited clean energy. It’s slow progress, but a new experiment on the Joint European Torus (JET) offers some hope. The team says Britain’s JET successfully sustained fusion for five seconds, producing enough power to power thousands of homes and consuming only a fraction of the fuel.

Fusion is the same process that powers the Sun and, indirectly, all life on Earth. Humanity has long been learning to produce energy by splitting the atom, but fusion is much more difficult to use. Stars like the Sun support fusion for eons due to their enormous mass and gravity, but the best we can do on Earth is a few seconds, usually with negative energy production. Still, five seconds of JET fusion is a big deal.

JET is a tokamak reactor, a toroidal chamber in which hydrogen isotopes are heated to high temperatures and held in a magnetic field. More than 300 scientists from the EUROfusion group participated in the latest JET tests, which heated deuterium and tritium to 150 million degrees Celsius (10 times hotter than the core of the Sun). When deuterium and tritium combine, you get a hydrogen atom and an extra neutron whose total mass is slightly less than that of the starting materials. This mass turns into energy, and a large part of it.

During this five-second thermonuclear fusion, JET produced 69 megajoules of energy. That’s enough to power 12,000 homes, but only for five seconds. Some reactors last longer, but tests are still best measured in seconds, and none produce that much useful power. And JET produced all this power using just 0.2 milligrams of fuel.

This was the last JET experiment; The project ended in December 2023 after more than 40 years. But the team used this latest test to demonstrate techniques that could help future research reactors reach even higher energy levels. The team successfully “mitigated” the intense heat emitted from the plasma by holding the edge of the plasma to prevent damage to the torus walls. None of these techniques have been tested in a deuterium-tritium environment before.

EUROfusion scientists believe that the work done at JET will have a significant impact on future experiments. They point to projects such as ITER in France, which will be the largest tokamak reactor in the world when completed in the coming years. Scientists hope that ITER’s successor, DEMO, will be able to produce 300 to 500 megawatts of electricity, but the team is targeting the middle of the century for this. ITER is expected to begin deuterium-tritium experiments in the mid-2030s.