Joint European Torus

This article is about the Joint European Torus. For the Japanese government initiative, see JET Programme. For other uses, see Jet (disambiguation).

JET

Type	Tokamak
Operation date	1983–
Major radius	2.96 m
Minor Radius	1.25–2.10 m
Plasma volume	100 m3
Magnetic field	3.45 T (toroidal)
Heating	38 MW

JET, the Joint European Torus, is a magnetic confinement plasma physics experiment located in Oxfordshire, England. It is currently the largest facility of its kind in operation. Its main purpose is to open the way to future nuclear fusion experimental tokamak reactors such as ITER and DEMO.

Construction

The reactor is situated on a retired Navy airfield near Culham, Oxfordshire – RNAS Culham (HMS Hornbill), in the UK: 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 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. Each 775 ton flywheel can spin up to 225 rpm. 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.

Operating history

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 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.

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.

• Weight of the vacuum vessel: 100 tonnes
• Weight of the toroidal field coils: 384 tonnes
• Weight of the iron core: 2800 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: 20–60 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: 20–60 s
• Auxiliary heating:
  • Neutral beam injection heating ≤23 MW
  • Radio frequency heating ≤15 MW
• 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 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

External links

• JET pages on the EFDA web site
• Culham Centre for Fusion Energy
• The United Kingdom Atomic Energy Authority
• IAEA's information about JET
• Photos from JET torus hall

Sources

• Fusion reactors explained by HowStuffWorks
• T. Fujita, et al., "High performance experiments in JT-60U reversed shear discharges", Nuclear Fusion, Vol 39, Page 1627 (1999)