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JET, the Joint European Torus, is the largest nuclear fusion experimental reactor yet built.

The reactor is situated on an old Navy airfield near Culham, Oxfordshire, in the UK: the construction of the buildings which house the project was undertaken by Tarmac Construction,[1] starting in 1978 with the Torus Hall being completed in January 1982. Construction of the experiment itself began immediately after the completion of the Torus Hall, with the first experiments beginning in 1983.

The components for the JET experiment came from manufacturers all over Europe, with these components transported to the site. Because of the extremely high power requirements for the tokamak, and the fact that power draw from the main grid is limited, two large flywheel generators were constructed to provide this necessary power. 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.

Equipment capabilityEdit

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 Q of approximately 0.7. Q is the ratio of fusion alpha heating power to input heating power. In order to achieve a burning plasma, a Q value greater than 1 is required. This figure does not include other power requirements for operation, most notably confinement. A commercial fusion reactor would probably need a Q value somewhere between 15 and 22. 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 estimated from experiments performed with a pure Deuterium (D-D) plasma. Similar extrapolations have not been made for JET, however 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 informationEdit

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  • Weight of the vacuum vessel: 100 tonnes
  • Weight of the toroidal field coils: 384 tonnes
  • Weight of the Iron Core: 2700 tonnes
  • Wall material: Primarily carbon fibre composite, Beryllium coated.
  • Plasma major radius: 2.96 m
  • Plasma minor radius: 2.10 m (vertical), 1.25 m (horizontal)
  • Flat top pulse length: 20 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: 20–60 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
    • Charge exchange spectroscopy – provides impurity ion temperature, density and rotation profiles
    • Interferometers – measure line integrated plasma density
    • Electron cyclotron emission antennas – fast, high resolution electron temperature profiles
    • Visible/UV/X-ray spectrometers – temperatures and densities
    • Neutron spectroscopy – Number of neutrons leaving the plasma relates directly to the fusion power. 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
    • Time resolved neutron yield monitor

Current statusEdit

JET was originally set up by Euratom with a discriminatory employment system that allowed non-British staff to be employed with 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 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 culminating in experiments using small amounts of tritium. For most of 2004 it was shut down for a series of major upgrades increasing total available heating power to over 40 MW, enabling further studies relevant to the development of ITER to be undertaken. In the future it is possible that JET-EP (Enhanced Performance) will further increase the record for fusion power.

In late September 2006, experimental campaign C16 was started. Its objective is to study ITER-like operation scenarios.


  1. Berry Ritchie, The Story of Tarmac Page 100, Published by James & James (Publishers) Ltd, 1999

External linksEdit



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