Joint European Torus
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- JET redirects here, at the article about the research experiment in nuclear physics; for other uses see Jet
JET, the Joint European Torus, is the largest nuclear fusion experimental reactor yet built.
Situated on an old Navy airfield near Culham, Oxfordshire, in the UK, construction was started in 1978 and the first experiments began in 1983.
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, a self-sustaining nuclear fusion reaction would have an infinite Q value (requiring no external heating). 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.
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[edit] Machine information
- Wall material: Primarily carbon fibre composite, Beryllium coated.
- Plasma major radius: 2.96m
- Plasma minor radius: 2.10m (vertical), 1.25m (horizontal)
- Toroidal magnetic field (on plasma axis): 3.45T
- Plasma current: 3.2MA (circular plasma), 4.8MA (D-shape plasma)
- Lifetime of the plasma: 20-60s
- 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 - energy and quantity of neutrons leaving plasma (relates directly to the rate of fusion reactions in the plasma)
- Bolometers - energy loss from the plasma
- Various material probes - inserted into the plasma to take direct measurements of flow rates and temperatures
[edit] Current status
In December 1999 JET came to an end of its international contract. The United Kingdom Atomic Energy Authority (UKAEA) took over the safety and operation of the JET facilities on behalf of its European partners. The experimental programme is as of 2000 being 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.
