The Joint European Torus (JET) at the UK Atomic Energy Authority’s (UKAEA’s) Culham facility has performed its final experiments, marking the end of 40 years of groundbreaking experiments. JET delivered pulse number 105,842 on 18 December over four decades after it delivered its first pulse on 25 June 1983. UKAEA CEO, Professor Sir Ian Chapman, who was present for the final plasma experiment, said: “This is the final milestone in JET’s 40-year history. Those decades of research using JET by dedicated teams of scientists and engineers have played a critical role in accelerating the development of fusion energy.”

According to UKAEA, JET’s final day of plasma “continued to push scientific boundaries, firstly attempting an inverted plasma shape for the first time at Culham before deliberately aiming electrons at the inner wall to improve understanding of beam control and damage mechanisms”. During delivery of the final pulse, JET ❤️ was engraved into one of its tiles.

As with previous research at JET, the findings of these experiments will support the development of the the International Experimental Thermonuclear Reactor (ITER) being built in Cadarache, France. JET has achieved a number of landmarks over the years, holding the title of the largest reactor of its type in the world until Japan’s Torus-60 Super Advanced (JT-60SA) fusion device began operation in November. Jet also achieved the world's first controlled release of fusion energy and in 1997 set a record thermal power output of 16 MW. In 2022 JET doubled previous records by producing a total of 59 megajoules of heat energy from fusion over a five second period.

JET will now move on to the next phase of its life cycle in early 2024 for repurposing and decommissioning, which will last until around 2040. However, even the decommissioning of JET will provide valuable information for the fusion community. "The decommissioning will look at analysing what has happened to the [reactor] materials and how they have changed. This will help better maintain other fusion sites," said Fernanda Rimini, JET Senior Exploitation Manager.

When the foundation stone for JET was laid in 1979, it was a multinational project comprising Belgium, Italy, Luxembourg, France, Netherlands, West Germany, Denmark, Ireland, Sweden, Switzerland, and the UK. It was subsequently operated by UKAEA jointly with scientists from 28 European countries through work coordinated by the EUROfusion consortium which manages and funds European fusion research activities on behalf of Euratom. However, UK ceased to be a member of EUROfusion after Brexit in 2020, which also compromised UK’s relations with ITER. A temporary framework for some forms of cooperation was agreed and discussions on possible future association continued. In September, the UK government decided to leave the Euratom Community for good but left the door open for potential collaboration with ITER.

The official government declaration said the UK had decided to pursue a domestic fusion energy strategy instead of associating to the EU's Euratom programme but that this “would involve close international collaboration, including with European partners, and a new, cutting-edge alternative programme, backed by up to £650m ($825m) to 2027." The European Commission acknowledged that this decision was “guided by the UK's assessment that its industry's long absence from Euratom and Fusion for Energy/ITER programmes cannot be reversed”. However, the UK made clear that it remained open to collaboration with the EU and ITER.

The UK’s fusion programme between now and 2027 includes development of the new Spherical Tokamak for Energy Production (STEP) prototype fusion energy plant too be sited in Nottinghamshire, aiming for 2040. The government is providing £220m to fund the first phase of STEP, which will see the UK Atomic Energy Authority (UKAEA) produce a concept design by 2024. The aim is to have a fully evolved design and approval to build by 2032, so that construction can begin.

Image: The JET control room on the day of final plasma experiments (courtesy of United Kingdom Atomic Energy Authority / EUROfusion)