Joint European Torus

JET, the Joint European Torus, is the world's largest operational magnetic confinement plasma physics experiment, located at Culham Science Centre in Oxfordshire, UK. Based on a tokamak design, the fusion research facility is a joint European project with a main purpose of opening the way to future nuclear fusion grid energy. More advanced facilities are being developed to follow on the JET research, including ITER and DEMO.


    The JET facilities are situated on a former Navy airfield near Culham, Oxfordshire – RNAS Culham (HMS Hornbill), in the UK. They are located alongside Culham Centre for Fusion Energy (the UK's fusion research laboratory, which opened in 1965). The construction of the buildings which house the project was undertaken by Tarmac Construction, starting in 1978 with the Torus Hall being completed in January 1982. Construction of the JET machine itself began immediately after the completion of the Torus Hall, with the first plasma experiments in 1983.

    The components for the JET machine came from manufacturers all over Europe, with these components transported to the site.

    Power requirements

    JET's power requirements during the plasma pulse are around 500 MW with peak in excess of 1000 MW. Because power draw from the main grid is limited to 575 MW, two large flywheel generators were constructed to provide this necessary power. Each 775-ton flywheel can spin up to 225 rpm and store 3.75 GJ. Each flywheel uses 8.8 MW to spin up and can generate 400 MW (briefly). One generator provides power for the 32 toroidal field coils, the other for inner poloidal field coils. The outer field coils draw their power from the grid. On a typical days the flywheels can be used 22 times. Even with the flywheels, each experimental run (up to 30 s)[not in citation given] puts a large load on the grid.



    • 1973 - Beginning of design work
    • 1977 - Culham site is chosen and the construction work begins
    • 25 June 1983 - Very first plasma achieved at JET
    • 9 April 1984 - JET officially opened by Her Majesty Queen Elizabeth II
    • 7 November 1991 - The world’s first controlled release of fusion energy
    • 1993 - JET converted to Divertor configuration
    • 1997 - JET produces 16 megawatts of fusion power (world record)
    • 1998 - Remote Handling first used for in-vessel work
    • 2000 - The collective use of JET and its scientific programme becomes managed through the European Fusion Development Agreement (EFDA)
    • 2006 - JET starts operation with ITER-like magnetic configurations
    • 2009-2011 Installation of the ITER-Like Wall

    Operating history

    In 1970 the Council of the European Community decided in favour of a robust fusion programme and provided the necessary legal framework for a European fusion device to be developed. Three years later, the design work began for the JET machine. In 1977 the construction work began and at the end of the same year a former Fleet Air Arm airfield at Culham in the UK was selected as the site for the JET project. In 1978 the "JET Joint Undertaking" was established as a legal entity. Only five years later the construction was completed on time and on budget. On 25 June 1983 the very first JET plasma was achieved and on 9 April 1984 Her Majesty Queen Elizabeth II officially opened this European fusion experiment.

    In the history of fusion research the year 1991 is particularly significant: on the 9th November a Preliminary Tritium Experiment achieved the world’s first controlled release of fusion power.[]

    Six years later, in 1997, another world record was achieved at JET: 16 mega watts of fusion power were produced from a total input power of 24 mega watts – a 65% ratio. This is equivalent to a release of 22 mega joules of energy. a total of 16 MW was measured for less than a second and 5 MW for 5 seconds.

    In 1998 JET’s engineers developed a remote handling system with which, for the first time, it was possible to exchange certain components using artificial hands only. A “Remote Handling” system is, in general, an essential tool for any subsequent fusion power plant and especially for the future experimental reactor, ITER.

    In 1999 the European Fusion Development Agreement (EFDA) was established with responsibility for the future collective use of JET. With the turn of the millennium the "Joint Undertaking" ended and the JET Facilities commenced operating under contract by CCFE (at that time UKAEA). From then, JET’s scientific programme was determined by EFDA. The sturdiness and flexibility of JET’s original design has made it possible for the device to evolve with the interests of the fusion community and meet the requirements of ITER. JET was converted to Divertor configuration in 1993 and started operation with ITER-like magnetic configurations in 2006. From October 2009 to May 2011 the ITER-Like Wall was installed.

    JET was originally set up by Euratom with a discriminatory employment system that allowed non-British staff to be employed at more than twice the salaries of their British equivalents. The British staff eventually had this practice declared illegal, and substantial damages were paid at the end of 1999 to UKAEA staff (and later to some contractors). This was the immediate cause of the ending of Euratom's operation of the facility.

    In December 1999, JET's international contract ended and the United Kingdom Atomic Energy Authority (UKAEA) then took over managing the safety and operation of the JET facilities on behalf of its European partners. From that time (2000), JET's experimental programme was then co-ordinated by the European Fusion Development Agreement (EFDA) Close Support Unit.

    JET operated throughout 2003, with the year culminating in experiments using small amounts of tritium. For most of 2004, JET was shut down for a series of major upgrades, increasing its total available heating power to over 40 MW, enabling further studies relevant to the development of ITER to be undertaken. In late September 2006, the C16 experimental campaign was started, with the objective of studying ITER-like operation scenarios.

    In October 2009, a 15-month shutdown period was started, and improvements were made to the tokamak, including replacing carbon components in the vacuum vessel with tungsten and beryllium ones, to bring JET's components more in line with those planned for ITER. Heating power was also increased by 50%, bringing the neutral beam power available to the plasma up to 34MW, and diagnostic and control capabilities were improved. In total, over 86,000 components were changed in the torus during the shutdown.

    In mid-May 2011, the shutdown reached its end. The first experimental campaign after the installation of the “ITER-Like Wall” started on 2 September 2011.

    On 14 July 2014 the European Commission signed a contract worth €283m for another 5-year extension so more advanced higher energy research can be performed at JET.

    Equipment capability

    JET is equipped with remote handling facilities to cope with the radioactivity produced by deuterium-tritium (D-T) fuel, which is the fuel proposed for the first generation of fusion power plants. Pending construction of ITER, JET remains the only large fusion reactor with facilities dedicated to handling the radioactivity released from D-T fusion. The power production record-breaking runs from JET and TFTR used 50–50 D-T fuel mixes.

    During a full D-T experimental campaign in 1997 JET achieved a world record peak fusion power of 16 MW which equates to a measured gain Q, of approximately 0.7. Q is the ratio of fusion power produced to input heating power. In order to achieve break-even, a Q value greater than 1 is required. A self-sustaining burning plasma requires at least Q=5 (since the alpha particles carry one fifth the fusion energy) and a power plant requires at least Q=10. As of 1998, a higher Q of 1.25 is claimed for the JT-60 tokamak; however, this was not achieved under real D-T conditions but extrapolated from experiments performed with a pure deuterium (D-D) plasma. Similar extrapolations have not been made for JET, but it is likely that increases in Q over the 1997 measurements could now be achieved if permission to run another full D-T campaign was granted. Work has now begun on ITER to further develop fusion power.

    Machine information

    Internal view of the JET tokamak superimposed with an image of a plasma taken with a visible spectrum video camera.
    • Cost: 198.8 Million European Units of Account (predecessor to the Euro). JET was completed in 1983. This is roughly 438 Million in 2014 US dollars.
    • Neutron Rate: at least 1.8×1016 neutrons per second.
    • Weight of the vacuum vessel: 100 tonnes
    • Weight of the toroidal field coils: 384 tonnes
    • Weight of the iron core: 2800 tonnes
    • Wall material: Entirely Beryllium save Tungsten 'exhaust'
    • Plasma major radius: 2.96 m
    • Plasma minor radius: 2.10 m (vertical), 1.25 m (horizontal)
    • Flat top pulse length: 20–60 s
    • Toroidal magnetic field (on plasma axis): 3.45 T
    • Plasma current: 3.2 MA (circular plasma), 4.8 MA (D-shape plasma)
    • Lifetime of the plasma: 5–30 s
    • Auxiliary heating:
    • Major diagnostics:
      • Visible/infrared video cameras
      • Numerous magnetic coils – provide magnetic field, current and energy measurements
      • Thomson scattering spectroscopy – provides electron temperature and electron density profiles of the plasma
      • – provides impurity ion temperature, density and rotation profiles
      • Interferometers – measure line integrated plasma density
      • antennas – fast, high resolution electron temperature profiles
      • Visible/UV/X-ray spectrometers – temperatures and densities
      • Neutron diagnostics:
        • Neutron counting: Number of neutrons leaving the plasma relates directly to the fusion power.
        • Neutron spectroscopy – Neutron energy relates to the ion velocity distribution and hence the fuel reactivity.
      • Bolometers – energy loss from the plasma
      • Various material probes – inserted into the plasma to take direct measurements of flow rates and temperatures
      • Soft X-ray cameras to examine MHD properties of plasmas
      • Time resolved neutron yield monitor
      • Hard X-ray monitors
      • Electron Cyclotron Emission Spatial Scanners

    Influence on ITER

    "Already JET experiments have helped ITER make the decision to begin operation with a full tungsten divertor, thus substantially reducing investment costs".


    Scientists in Oxfordshire are planning fusion tests using Deuterium-Tritium plasmas for 2018. They hope to break their own record of 16 megawatts of fusion power.

    See also