Europe’s flagship tokamak closes four decades of operation with its third and final deuterium-tritium campaign, delivering results that will underpin ITER and the first fusion power plants.
A unique machine, a unique opportunity
JET, the Joint European Torus at Culham (UK), is – together with the USA’s now-shutdown TFTR – the only tokamak up to now capable of operating with deuterium-tritium (D-T) fuel, the same reaction that will power ITER and the first-of-a-kind (FOAK) fusion power plants to follow. Engineered to confine up to 90% of the alpha particles produced by fusion reactions, JET has spent over 40 years generating plasma conditions that no other device in the world can currently reproduce. Between 2022 and 2023, operating under EUROfusion’s Tokamak Exploitation Work Package (WPTE), JET completed its final experimental campaigns – culminating in DTE3, its third and last D-T campaign – before entering decommissioning in December 2023. The outcome of this extensive effort has been presented as an Overview contribution to the last IAEA Fusion Energy Conference in Chengdu and finally published recently on Nuclear Fusion (N. Vianello et al 2026 Nucl. Fusion 66 116010, “Results from the last DD and DT JET campaigns in the framework of the EUROfusion Tokamak Exploitation Work Package activity”, open access).
A Europe-wide scientific effort
This final programme drew on close to 400 scientists and engineers from institutions across Europe and international partners, coordinated through the WPTE. JET’s results were pursued jointly with medium-size tokamaks – ASDEX Upgrade, MAST-U, TCV and WEST – in a stepladder approach that extrapolates physics understanding from smaller devices up to JET’s scale, and ultimately to ITER. The scale of this collaboration reflects the complexity of the challenge: integrating scenario development, exhaust control, plasma-wall interaction, and tritium management under conditions approaching those of a burning plasma.
What the final campaigns achieved
The results speak for themselves. JET set a new fusion energy record of 69 MJ in tritium-rich hybrid plasmas, the highest ever produced by a fusion device. In parallel, the team demonstrated an ITER-relevant integrated scenario, sustaining high confinement (H98 ≈ 0.85) at 3 MA in D-T plasmas with a partially detached divertor – showing that reactor-grade performance and heat exhaust control can coexist. Two advanced exhaust regimes, quasi-continuous exhaust (QCE) and the X-point radiator (XPR), which avoid the damaging transient heat loads typical of conventional operation, were established first in deuterium and then successfully extended to D-T plasmas. JET also pushed the duration of reactor-relevant regimes, sustaining H-mode plasmas for up to 60 seconds. On the safety side, extensive use of JET’s shattered pellet injector generated critical data now feeding directly into the design of ITER’s disruption mitigation system, while comprehensive fuel-retention studies – combining gas-balance measurements, post-mortem analysis and laser-induced desorption spectroscopy – delivered essential input for how ITER will track and manage its tritium inventory.
A legacy that outlives the machine
With JET now the last operating D-T-capable tokamak until next step devices including ITER will start their D-T phase, the datasets generated in these final campaigns are effectively irreplaceable. They are already validating predictive models, contributing to shared international databases such as the Coordination on International Challenges on Long duration OPeration (CICLOP) database , and informing the design of first-of-a-kind fusion power plants. Beyond the physics, JET’s final years leave behind decades of operational experience in handling tritium and nuclear-grade components – practical, hard-won knowledge that no simulation can substitute, and that will directly shape how ITER and future power plants are safely operated.
Source: N. Vianello et al 2026 Nucl. Fusion 66 116010, “Results from the last DD and DT JET campaigns in the framework of the EUROfusion Tokamak Exploitation Work Package activity”, open access.
The link to the article:
https://iopscience.iop.org/article/10.1088/1741-4326/ae71ec
DOI 10.1088/1741-4326/ae71ec
The direct link to the pdf version:
https://iopscience.iop.org/article/10.1088/1741-4326/ae71ec/pdf
Link to the references to the slides of the conference in connection to this publication/paper and presentation