Since Lev Artsimovich’s 1968 presentation of the T-3 tokamak, which had achieved a plasma temperature of about 10 million kelvin, the tokamak principle has been regarded as one of the most promising routes to thermonuclear fusion. Tokamak research then expanded rapidly around the world, and more than fifty devices have been built. Many have since been rebuilt or upgraded to incorporate new scientific and technological advances, while others are under construction or planned.

JET, Joint European Torus

JET tokamak.

JET, operated by the Culham Centre for Fusion Energy in the United Kingdom, was one of the world’s largest and most important experimental tokamaks. It achieved its first plasma in 1983 and completed experimental operation in 2023 after four decades of fusion research. JET had a major radius of 2.95 metres and a minor radius of about 1.25 metres and played a central role in developing reactor-relevant plasma scenarios.

JET used 32 copper toroidal field coils, each weighing about 12 tonnes. It was one of the first large tokamaks designed with a D-shaped vacuum vessel, which allowed flexible plasma shaping and the later introduction of a divertor. JET carried out its first deuterium-tritium experiments in 1991, followed by a major D–T campaign in 1997. In 1997, JET came closer to scientific breakeven than any tokamak before or since, producing 16.1 MW of fusion power and reaching a fusion gain factor of Q = 0.67. Here, Q is the ratio of fusion power produced to the external heating power supplied to the plasma.

Operation with tritium and high-energy fusion neutrons provided valuable reactor-relevant data but also activated components inside the vacuum vessel. JET therefore pioneered remote maintenance techniques using remotely operated manipulators to replace in-vessel components. Much of the experience gained at JET contributed directly to the design of ITER.

In 2009–2011, JET was fitted with an ITER-Like Wall using beryllium in the main chamber and tungsten in the divertor to test reactor-relevant plasma-facing materials. In its final deuterium–tritium campaign in 2023, JET produced a record 69 MJ of fusion energy. Because plasma pulses required very high electrical power, two large flywheel generators supplied additional energy during experiments.

TFTR, Tokamak Fusion Test Reactor

TFTR tokamak, 1989.

TFTR, operated by the Princeton Plasma Physics Laboratory in the United States, was the second major tokamak to conduct extensive experiments with deuterium–tritium fuel. It was designed with scientific breakeven as a major goal, although it did not achieve it. Nevertheless, TFTR set numerous records in plasma performance, including an ion temperature of about 510 million kelvin in 1995.

TFTR also achieved record values of the fusion triple product, combining plasma density, temperature and energy confinement time. In the mid-1990s, researchers demonstrated the enhanced reversed-shear confinement regime, which significantly reduced turbulent transport and improved plasma performance.

TFTR had a circular vacuum vessel with a major radius of about 2.6 metres and a minor radius of about 0.9 metres, surrounded by twelve copper toroidal field coils. It operated from 1982 to 1997. Its subsequent decommissioning provided a rare opportunity to examine materials that had been exposed to fusion neutrons.

JT-60SA, Japan Torus-60 Super Advanced

JT-60SA, operated in Naka, Japan, is currently the world’s largest operating tokamak, with a plasma volume of about 160 m³. It achieved its first plasma in 2023 and is the successor to JT-60U, which itself evolved from the original JT-60 device that began operation in 1985.

JT-60 and JT-60U achieved several major fusion records, including exceptionally high ion temperatures and fusion triple-product values. JT-60SA is designed for plasma pulses exceeding 100 seconds and will operate with hydrogen or deuterium rather than tritium. Its powerful auxiliary heating systems are intended to produce reactor-relevant plasma temperatures.

JT-60SA uses 18 D-shaped NbTi superconducting toroidal field coils cooled to about 4 K. Each coil is approximately 7.5 metres high and 4.5 metres wide, and the complete set weighs about 370 tonnes. The device is a major joint Japanese-European experiment designed to develop advanced plasma scenarios and support preparation for ITER operation.

EAST, Experimental Advanced Superconducting Tokamak

Technical sketch of the EAST tokamak.

EAST is a superconducting tokamak located in Hefei, China. It achieved its first plasma in 2006 and has since set several important records in high-temperature and long-pulse plasma operation. In 2025, EAST sustained a plasma for more than 1,000 seconds, demonstrating the long-duration operation required for future fusion devices. EAST uses superconducting toroidal and poloidal field coils and has a major radius of about 1.7 metres and a minor radius of about 0.4 metres. Its long-pulse experiments are aimed at demonstrating stable high-performance plasma operation over reactor-relevant timescales.

WEST is an Acronym for “W Environment in Steady-state Tokamak”

Vacuum vessel of WEST, formerly Tore Supra.

WEST, where W denotes tungsten, is located at Cadarache in France and is the successor to the Tore Supra tokamak, which began operation in 1988. Following extensive modernisation, WEST achieved its first plasma in 2016 and now serves as a test bed for ITER-relevant plasma-facing components and long-pulse operation. In February 2025, WEST set a world record by sustaining a plasma for 1,337 seconds, or more than 22 minutes.

WEST was modified to operate with an ITER-relevant divertor configuration and extensive tungsten plasma-facing components. It is equipped with superconducting magnets and actively cooled plasma-facing components, allowing very long plasma discharges. These features make WEST particularly valuable for testing heat exhaust, tungsten behaviour and long-pulse technologies relevant to ITER and future fusion power plants.

3 pictures

3 pictures