Joint European Torus

Joint European Torus
Name	Joint European Torus
Caption	The interior of the JET tokamak, showing plasma-facing components.
Location	Culham, Oxfordshire, United Kingdom
Affiliation	UK Atomic Energy Authority (host), European Consortium for the Development of Fusion Energy (operator)
Type	Tokamak
Field	Nuclear fusion
Built	1978–1983
Operated	1983–2023
Website	https://www.euro-fusion.org/jet/

Contents

Overview
History and construction
Scientific objectives and achievements
Technical specifications
Role in ITER and future projects
See also

Joint European Torus. The Joint European Torus was the world's largest and most powerful operational tokamak experiment for most of its operational lifetime, serving as the central research facility for the European Union's fusion power program. Located at the Culham Centre for Fusion Energy in the United Kingdom, it was designed and used to study the physics of plasmas under conditions similar to those required for a future fusion power plant. Its pioneering work, particularly in using a deuterium-tritium fuel mix, provided critical data for the design of the international ITER project and demonstrated the scientific feasibility of sustained fusion energy.

Overview

The facility was constructed and operated by the European Consortium for the Development of Fusion Energy (EUROfusion) under a contract with the European Atomic Energy Community (Euratom). As a major big science project, it brought together hundreds of scientists and engineers from across Europe, with its research program coordinated by the JET Joint Undertaking. The tokamak's primary goal was to explore the plasma physics and engineering challenges of magnetic confinement fusion, acting as a vital testbed for technologies and materials needed for a fusion reactor. Its success firmly established the tokamak as the leading design for future fusion devices and made significant contributions to the global fusion research community, including collaborations with facilities like the JT-60 in Japan and the DIII-D in the United States.

History and construction

The project was proposed in the early 1970s, with the European Commission selecting the Culham site in 1977 following a competition against a proposal from Garching in West Germany. Construction began in 1978, with the machine assembly led by an international industrial consortium. A key early decision was to construct the vacuum vessel from Inconel and later install an internal beryllium and tungsten divertor, known as the ITER-Like Wall, which was a major upgrade completed in 2011. The first plasma was achieved in June 1983, and the device was officially inaugurated by Queen Elizabeth II in 1984. Throughout its life, it underwent several major upgrades, including the installation of a neutral beam injection system for plasma heating and the Mark II divertor, to enhance its performance and diagnostic capabilities.

Scientific objectives and achievements

Its core scientific mission was to achieve and study high-performance plasmas, culminating in world-record-breaking fusion energy yields. In 1991, it became the first device to produce controlled fusion power using a deuterium-tritium fuel mixture, and in 1997 it set the longstanding world record for fusion energy output, producing 16 megawatts of power. Later campaigns focused on sustaining high-performance H-mode plasmas and testing plasma-facing materials compatible with a reactor environment. Experiments with the ITER-Like Wall provided invaluable data on fuel retention and material behavior, directly informing the design choices for ITER. Its final deuterium-tritium experiments in 2021, known as the DTE2 campaign, again broke its own record, achieving 59 megajoules of sustained fusion energy.

Technical specifications

The machine was a large, D-shaped tokamak with a major radius of 2.96 meters and a minor radius of 1.25 meters. Its toroidal magnetic field, produced by 32 copper magnets, could reach up to 3.45 tesla. The plasma volume was approximately 100 cubic meters, and it could heat plasmas to over 100 million degrees Celsius using systems including ion cyclotron resonance heating and neutral beam injectors capable of delivering up to 34 megawatts of power. The vacuum vessel, with its installed ITER-Like Wall, was designed to handle the intense heat and neutron flux from fusion reactions, making it a unique test facility for reactor-grade materials.

Role in ITER and future projects

It served as the essential physics and technology precursor to the ITER project, with its size and plasma parameters providing the closest possible scale model of the larger international device. Data from its experiments were used to validate plasma confinement scaling laws, refine heating and control schemes, and develop remote handling techniques using its MASCOT and ITER Remote Handling System test platforms. The knowledge gained directly shaped the operational plans and safety cases for ITER. Furthermore, its legacy informs the design of European demonstration power plant (DEMO) concepts and other national programs like the STEP project in the United Kingdom.