The Joint European Torus (JET) was a magnetically confined plasma physics experiment, located at Culham Centre for Fusion Energy in Oxfordshire, UK.

JET began operation in 1983 and spent most of the next decade increasing its performance in a lengthy series of experiments and upgrades.

[1] Between 2009 and 2011, JET was shut down to rebuild many of its parts, to adopt concepts being used in the development of the ITER project in Saint-Paul-lès-Durance, in Provence, southern France.

[5] As a large tokamak experiment, JET was designed to study plasma behaviour in conditions and dimensions approaching those required in a fusion reactor.

Many initially promising experimental paths had all failed to produce useful results, and the latest experiments suggested performance was stalled at the Bohm diffusion limit, far below what would be needed for a practical fusion generator.

[8][9] A key issue in tokamak designs was that they did not generate enough of an electric current in their plasma to provide enough heating to bring the fuel to fusion conditions.

One of these, the Princeton Large Torus (PLT) demonstrated that neutral beam injection was a workable concept, using it to reach record temperatures well over the 50 million K that is the minimum needed for a practical reactor.

Once breakeven is achieved, even small improvements from that point begin to rapidly increase the amount of net energy being released.

[17] JET was one of only two tokamak models designed to work with a real deuterium-tritium fuel mix, the other being the US-built TFTR.

An advanced tokamak capable of reaching scientific breakeven would have to be very large and very expensive, which led to the international effort ITER.

[25] Performance was significantly improved, allowing JET to set many records in terms of confinement time, temperature and fusion triple product.

[29][30] In 1998, JET's engineers developed a remote handling system with which, for the first time, it was possible to exchange certain components using artificial hands only.

A "Remote Handling" system is, in general, an essential tool for any subsequent fusion power plant and especially for the International Thermonuclear Experimental Reactor (ITER) being developed at Saint-Paul-lès-Durance, in Provence, southern France.

[32] In October 2009, a 15-month shutdown period was started to rebuild many parts of the JET to adopt concepts being used in the development of the ITER project in Saint-Paul-lès-Durance, in Provence, southern France.

[35] On 14 July 2014, the European Commission signed a contract worth €283m for another 5-year extension so more advanced higher energy research can be performed at JET.

[37] Talks on the funding after 2018, when the 5-year plan expired, commenced and a new agreement to extend JET's operation until 2019 or 2020 appeared to be largely complete.

[28][40] In October 2023, JET set its final fusion energy record, producing 69.29 megajoules over 6 seconds from only 0.21 mg of D-T fuel.

[45] The total plasma volume within it is 100 cubic metres, about 100 times larger than the largest machine in production when the JET design began.

Ideally, the magnets surrounding the chamber should be more curved at the top and bottom and less on the inside and outsides in order to support these forces, which leads to something like an oval shape that the D closely approximated.

[52] Each 775-ton flywheel can spin up to 225 rpm and store 3.75 GJ,[53] roughly the same amount of kinetic energy as a train weighing 5,000 tons traveling at 140 kilometres per hour (87 mph).