Across three landmark campaigns in 1991, 1997, and 2021–2023, the Joint European Torus set successive world records for controlled fusion energy and provided critical data for ITER's design.
The Joint European Torus (JET), located at the Culham Centre for Fusion Energy in Oxfordshire, United Kingdom, operated from 1983 to December 2023 as the world's largest magnetic-confinement fusion experiment. With a major radius of approximately 3 meters and a D-shaped plasma cross-section, JET was purpose-built to explore reactor-relevant conditions. Its unique distinction among the world's tokamaks was its ability to handle tritium fuel, making it the only facility capable of full deuterium–tritium (D-T) experiments until ITER begins operations.1
On November 9, 1991, JET became the first tokamak to produce controlled fusion power from a D-T plasma. The Preliminary Tritium Experiment (PTE) used a small fraction of tritium mixed with deuterium (roughly 10 percent tritium by ion count) and generated a peak fusion power of approximately 1.7 MW. While modest, the result confirmed that tritium could be safely introduced and handled in a large tokamak and that the resulting neutron production matched theoretical predictions.2
JET's first full D-T Experiment (DTE1) campaign in 1997 pushed performance dramatically higher. Using optimized plasma scenarios with neutral-beam injection and ion-cyclotron resonance heating, JET achieved a peak fusion power of 16.1 MW — a world record that would stand for more than two decades. The experiment also set a record for sustained fusion energy, producing 21.7 MJ in a single pulse. The D-T plasmas in DTE1 demonstrated the importance of isotope effects on confinement and provided the first comprehensive dataset for validating models of alpha-particle heating in a burning plasma.3
Beginning in late 2021, JET embarked on a final series of D-T campaigns designated DTE2 and DTE3. In December 2021, JET set a new world record for sustained fusion energy: 59 MJ produced over a five-second pulse — nearly tripling the 1997 mark. The peak power during these pulses reached roughly 11 MW, lower than the 1997 spike but sustained over a much longer period. The achievement demonstrated reliable quasi-steady-state D-T operation with ITER-relevant wall materials (a beryllium-and-tungsten first wall installed during the 2009–2011 ITER-Like Wall project).4
The DTE3 campaign in 2023 continued to refine understanding of tritium retention, neutron damage, and plasma–wall interactions in reactor-relevant conditions. By the time JET conducted its final plasma pulse on December 18, 2023, the machine had provided an irreplaceable bridge between present-day experiments and ITER's operational regime.
JET's D-T campaigns remain the only magnetic-confinement experiments to have operated with reactor fuel at significant power levels. The data underpin ITER's confinement projections, its tritium-handling procedures, and its choice of wall materials. JET's forty-year run trained generations of fusion scientists and engineers across Europe and beyond.5