The last series of experiments ended on the JET (Joint European Torus) tokamak, 40 years after its launch.

On 25 June 1983, the first plasma was obtained on this device, four decades later - on Monday, 18 December 2023, at 10:06 p.m., the last plasma discharge number 105842 was observed. It was the last experiment on JET and the end of a certain era.

UKAEA Chief Executive Officer, Prof Sir Ian Chapman, who was in attendance in JET’s Control Room 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."

Researchers from European research centres being part of the EUROfusion consortium, including scientists from the Institute of Plasma Physics and Laser Microfusion, on 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. The findings of these experiments will support the development and operation of ITER in France.

JET will now move on to the next phase of its life cycle in early 2024 for repurposing and decommissioning, and final shutdown which will last until c.2040.

UKAEA is currently developing the STEP (Spherical Tokamak for Energy Production) programme aimed at demonstrating the ability to generate net electricity from nuclear fusion.

A group of researchers during the last experimental campaign at the JET tokamak, including a team of the IPPLM employees (December 2023). Photo: © IPPLM

About JET

JET is the largest and most successful fusion experiment in the world, and a central research facility of the European Fusion Programme. JET is based at the UKAEA campus in Culham, Oxfordshire, UK and is collectively used by more than 31 European laboratories under the management of the EUROfusion consortium involving the participation of more than 350 researchers and engineers from all over Europe including Poland.

JET tokamak is an experimental torus-shaped fusion reactor that uses magnetic fields to keep hot, ionized gas (plasma) away from the inner walls of the vessel, allowing it to operate safely at temperatures of 150 million degrees Celsius - ten times hotter than the temperature at the centre of the Sun.

The core of the reactor is a vacuum chamber in which plasma is held in place by strong magnetic fields. In the current configuration, the main and minor radii of the plasma torus are 3 and 0.9 meters, respectively, and the total plasma volume is 90 cubic meters. A diverter located at the bottom of the vacuum chamber allows controlled removal of escaping heat and gas.

JET commenced operation in 1983 as a joint European project, undergoing several enhancements to improve its performance over the years. In 1991, JET became the world's first reactor to operate using a 50–50 mix of tritium and deuterium. The facility set numerous fusion records including a record Q-plasma (the ratio of the fusion power produced to the external power put in to heat the plasma) of 0.64 in 1997. Since 2011, the first wall of the vacuum chamber was made of beryllium and tungsten, which was to reflect the materials selected for the construction of the ITER reactor, i.e. the so-called ITER LIKE WALL. The next fusion energy record output of 59 megajoules in a five-second pulse was accomplished in December 2021. Built by Europe and used collaboratively by European researchers over its lifetime, JET became UKAEA property in October 2021.

Source: UKAEA, IPPLM