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The Joint European Torus, or JET, is an operational magnetically confined
plasma physics Plasma ()πλάσμα
, Henry George Liddell, R ...
experiment, located at
Culham Centre for Fusion Energy The Culham Centre for Fusion Energy (CCFE) is the UK's national laboratory for fusion research. It is located at the Culham Science Centre, near Culham, Oxfordshire, and is the site of the Joint European Torus (JET), Mega Ampere Spherical Tokam ...
in
Oxfordshire Oxfordshire is a ceremonial and non-metropolitan county in the north west of South East England. It is a mainly rural county, with its largest settlement being the city of Oxford. The county is a centre of research and development, primarily ...
, UK. Based on a
tokamak A tokamak (; russian: токамáк; otk, 𐱃𐰸𐰢𐰴, Toḳamaḳ) is a device which uses a powerful magnetic field to confine plasma in the shape of a torus. The tokamak is one of several types of magnetic confinement devices being d ...
design, the fusion research facility is a joint European project with a main purpose of opening the way to future
nuclear fusion Nuclear fusion is a reaction in which two or more atomic nuclei are combined to form one or more different atomic nuclei and subatomic particles (neutrons or protons). The difference in mass between the reactants and products is manife ...
grid energy. At the time of its design JET was larger than any comparable machine. JET was built with the hope of reaching ''scientific breakeven'' where the
fusion energy gain factor A fusion energy gain factor, usually expressed with the symbol ''Q'', is the ratio of fusion power produced in a nuclear fusion reactor to the power required to maintain the plasma in steady state. The condition of ''Q'' = 1, when the power bei ...
''Q'' =1.0. It began operation in 1983 and spent most of the next decade increasing its performance in a lengthy series of experiments and upgrades. In 1991 the first experiments including
tritium Tritium ( or , ) or hydrogen-3 (symbol T or H) is a rare and radioactive isotope of hydrogen with half-life about 12 years. The nucleus of tritium (t, sometimes called a ''triton'') contains one proton and two neutrons, whereas the nucleus o ...
were made, making JET the first reactor in the world to run on the production fuel of a 50–50 mix of tritium and
deuterium Deuterium (or hydrogen-2, symbol or deuterium, also known as heavy hydrogen) is one of two stable isotopes of hydrogen (the other being protium, or hydrogen-1). The nucleus of a deuterium atom, called a deuteron, contains one proton and one ...
. It was also decided to add a
divertor In nuclear fusion power research, a divertor is a device within a tokamak or a stellarator that allows the online removal of waste material from the plasma while the reactor is still operating. This allows control over the buildup of fusion p ...
design to JET, which occurred between 1991 and 1993. Performance was significantly improved, and in 1997 JET set the record for the closest approach to scientific breakeven, reaching ''Q'' = 0.67 in 1997, producing 16 MW of fusion power while injecting 24 MW of thermal power to heat the fuel. Between 2009 and 2011, JET was shut down to rebuild many of its parts, to adopt concepts being used in the development of the
ITER ITER (initially the International Thermonuclear Experimental Reactor, ''iter'' meaning "the way" or "the path" in Latin) is an international nuclear fusion research and engineering megaproject aimed at creating energy by replicating, on Eart ...
project in
Saint-Paul-lès-Durance Saint-Paul-lès-Durance (, literally ''Saint-Paul near Durance''; also spelled Saint-Paul-lez-Durance; Provençal: ''Sant Pau de Durença'') is a commune in the Bouches-du-Rhône department in Provence, southern France. The Cadarache research ...
, in
Provence Provence (, , , , ; oc, Provença or ''Prouvènço'' , ) is a geographical region and historical province of southeastern France, which extends from the left bank of the lower Rhône to the west to the Italian border to the east; it is bor ...
, southern France. In December 2020, a JET upgrade commenced using tritium, as part of its contribution to ITER. On 21 December 2021, using deuterium-tritium fuel, JET produced 59 megajoules during a five second pulse, beating its previous 1997 record of 21.7 megajoules, with ''Q'' = 0.33.


History


Background

By the early 1960s, the fusion research community was in the "doldrums". Many initially promising experimental paths had all failed to produce useful results, and the latest experiments suggested performance was stalled out at the
Bohm diffusion The diffusion of plasma across a magnetic field was conjectured to follow the Bohm diffusion scaling as indicated from the early plasma experiments of very lossy machines. This predicted that the rate of diffusion was linear with temperature and in ...
limit, far below what would be needed for a practical fusion generator. In 1968, the Soviets held the periodic meeting of fusion researchers in
Novosibirsk Novosibirsk (, also ; rus, Новосиби́рск, p=nəvəsʲɪˈbʲirsk, a=ru-Новосибирск.ogg) is the largest city and administrative centre of Novosibirsk Oblast and Siberian Federal District in Russia. As of the 2021 Censu ...
, where they introduced data from their T-3 tokamak. This represented a dramatic leap in fusion performance, at least 10 times what the best machines in the world had produced to that point. The results were so good that some dismissed them as faulty measurements. To counter this, the Soviets invited a team from the UK to independently test their machine. Their 1969 report confirmed the Soviet results, resulting in a "veritable stampede" of tokamak construction around the world. A key issue in tokamak designs was that they did not generate enough of an electrical current in their plasma to provide enough heating to bring the fuel to fusion conditions. Some sort of external heating would be required. There was no shortage of ideas for this, and in the mid-1970s a series of machines were built around the world to explore these concepts. One of these, the Princeton Large Torus (PLT) demonstrated that neutral beam injection was a workable concept, using it to reach record temperatures well over the 50 million K that is the minimum needed for a practical reactor. With the PLT's success, the path to scientific breakeven finally appeared possible after decades of effort. Scientific breakeven is the point where the power produced by the fusion reactions is equal to the amount of power injected to heat the plasma. Once breakeven is achieved, even small improvements from that point begin to rapidly increase the amount of net energy being released. Teams around the world began planning for a new generation of machines combining PLT's injectors with
superconducting Superconductivity is a set of physical properties observed in certain materials where electrical resistance vanishes and magnetic flux fields are expelled from the material. Any material exhibiting these properties is a superconductor. Unlike ...
magnets and vacuum vessels that could hold deuterium-tritium fuel instead of the test fuels containing pure deuterium or
hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxi ...
that had been used up to that point.


European design

In 1971, the member states of the
European Atomic Energy Community The European Atomic Energy Community (EAEC or Euratom) is an international organisation established by the Euratom Treaty on 25 March 1957 with the original purpose of creating a specialist market for nuclear power in Europe, by developing nuc ...
(Euratom) decided in favour of a robust fusion programme and provided the necessary legal framework for a European fusion device to be developed. In 1975, the first proposals for the JET machine were completed. Detailed design took three years. At the end of 1977, after a long debate, Culham was chosen as the host site for the new design. Funding was approved on 1 April 1978 as the "JET Joint Undertaking" legal entity. The reactor was built at a new site next to the
Culham Centre for Fusion Energy The Culham Centre for Fusion Energy (CCFE) is the UK's national laboratory for fusion research. It is located at the Culham Science Centre, near Culham, Oxfordshire, and is the site of the Joint European Torus (JET), Mega Ampere Spherical Tokam ...
, the UK's fusion research laboratory which opened in 1965. The construction of the buildings was undertaken by Tarmac Construction, starting in 1978 with the Torus Hall. The Hall was completed in January 1982 and construction of the JET machine itself began immediately after the completion of the Torus Hall. The cost was 198.8 Million European Units of Account (predecessor to the Euro) or 438 million in 2014 US dollars. JET was one of only two tokamak models designed to work with a real
deuterium Deuterium (or hydrogen-2, symbol or deuterium, also known as heavy hydrogen) is one of two stable isotopes of hydrogen (the other being protium, or hydrogen-1). The nucleus of a deuterium atom, called a deuteron, contains one proton and one ...
-
tritium Tritium ( or , ) or hydrogen-3 (symbol T or H) is a rare and radioactive isotope of hydrogen with half-life about 12 years. The nucleus of tritium (t, sometimes called a ''triton'') contains one proton and two neutrons, whereas the nucleus o ...
fuel mix, the other being the US-built
TFTR The Tokamak Fusion Test Reactor (TFTR) was an experimental tokamak built at Princeton Plasma Physics Laboratory (PPPL) circa 1980 and entering service in 1982. TFTR was designed with the explicit goal of reaching scientific breakeven, the point w ...
. Both were built with the hope of reaching ''scientific breakeven'' where the "fusion energy gain factor" or ''Q'' = 1.0. JET achieved its first plasma on 25 June 1983. It was officially opened on 9 April 1984 by
Queen Elizabeth II Elizabeth II (Elizabeth Alexandra Mary; 21 April 1926 – 8 September 2022) was Queen of the United Kingdom and other Commonwealth realms from 6 February 1952 until her death in 2022. She was queen regnant of 32 sovereign states during ...
. On 9 November 1991, JET performed the world's first deuterium-tritium experiment. This beat the US's machine, TFTR, by a full two years.


Upgrades

Although very successful, JET and its counterpart TFTR failed to reach scientific breakeven. This was due to a variety of effects that had not been seen in previous machines operating at lower densities and pressures. Based on these results, and a number of advances in plasma shaping and divertor design, a new tokamak layout emerged, sometimes known as an "advanced tokamak". An advanced tokamak capable of reaching scientific breakeven would have to be very large and very expensive, which led to the international effort
ITER ITER (initially the International Thermonuclear Experimental Reactor, ''iter'' meaning "the way" or "the path" in Latin) is an international nuclear fusion research and engineering megaproject aimed at creating energy by replicating, on Eart ...
. In 1991, the first experiments including
tritium Tritium ( or , ) or hydrogen-3 (symbol T or H) is a rare and radioactive isotope of hydrogen with half-life about 12 years. The nucleus of tritium (t, sometimes called a ''triton'') contains one proton and two neutrons, whereas the nucleus o ...
were made, allowing JET to run on the production fuel of a 50–50 mix of tritium and
deuterium Deuterium (or hydrogen-2, symbol or deuterium, also known as heavy hydrogen) is one of two stable isotopes of hydrogen (the other being protium, or hydrogen-1). The nucleus of a deuterium atom, called a deuteron, contains one proton and one ...
. It was also decided at this time to add a divertor, allowing removal of waste material from the plasma. Performance was significantly improved, allowing JET to set many records in terms of confinement time, temperature and
fusion triple product The Lawson criterion is a figure of merit used in nuclear fusion research. It compares the rate of energy being generated by fusion reactions within the fusion fuel to the rate of energy losses to the environment. When the rate of production is ...
. In 1997, JET set the record for the closest approach to scientific breakeven. It attained ''Q'' = 0.67, producing 16 MW of fusion energy while injecting 24 MW of thermal power to heat the fuel, a record that endured until 2021. This was also the record for greatest fusion power produced. 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
International Thermonuclear Experimental Reactor ITER (initially the International Thermonuclear Experimental Reactor, ''iter'' meaning "the way" or "the path" in Latin) is an international nuclear fusion research and engineering megaproject aimed at creating energy by replicating, on Eart ...
(ITER) being developed at
Saint-Paul-lès-Durance Saint-Paul-lès-Durance (, literally ''Saint-Paul near Durance''; also spelled Saint-Paul-lez-Durance; Provençal: ''Sant Pau de Durença'') is a commune in the Bouches-du-Rhône department in Provence, southern France. The Cadarache research ...
, in
Provence Provence (, , , , ; oc, Provença or ''Prouvènço'' , ) is a geographical region and historical province of southeastern France, which extends from the left bank of the lower Rhône to the west to the Italian border to the east; it is bor ...
, southern France. This Remote Handling system was later to lead on to become
RACE (Remote Applications in Challenging Environments) Remote Applications in Challenging Environments (RACE) is a remote handling and robotics test facility located at Culham Science Centre near Oxford, UK, operated by UKAEA. As part of the UK Government's Robotics and Autonomous Systems Strategy ( ...
. In 1999, the
European Fusion Development Agreement EFDA (1999 — 2013) has been followed by EUROfusion, which is a consortium of national fusion research institutes located in the European Union and Switzerland. The European Union has a strongly coordinated nuclear fusion research programme. At ...
(EFDA) was established with responsibility for the future collective use of JET.


ITER design work

In October 2009, a 15-month shutdown period was started to rebuild many parts of the JET to adopt concepts from the ITER design. This including replacing carbon components in the vacuum vessel with
tungsten Tungsten, or wolfram, is a chemical element with the symbol W and atomic number 74. Tungsten is a rare metal found naturally on Earth almost exclusively as compounds with other elements. It was identified as a new element in 1781 and first isola ...
and beryllium ones. 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.


Post-Brexit

Brexit threw the plans for JET in doubt. As part of its plan to leave the EU, the UK was to leave Euratom, which provides the funding for JET. Talks on the funding after 2018, when the 5-year plan expired, commenced and a new agreement to extend JET's operation until 2019 or 2020 appeared to be largely complete. These talks were put on hold after the Brexit announcement. However, in March 2019, the UK Government and European Commission signed a contract extension for JET. This guaranteed JET operations until the end of 2024 regardless of Brexit situation. In December 2020, a JET upgrade commenced using tritium, as part of its contribution to ITER. On 21 December 2021, JET produced 59 megajoules using deuterium-tritium fuel while sustaining fusion during a five second pulse, beating its previous record of 21.7 megajoules with Q = 0.33, set in 1997.


Description

JET has a major radius of 3 metres, and the D-shaped vacuum chamber is 2.5 metres wide and 4.2 metres high. The total plasma volume within it is 100 cubic metres, about 100 times larger than the largest machine in production when the JET design began. JET was one of the first tokamaks to be designed to use a D-shaped vacuum chamber. This was initially considered as a way to improve the safety factor, but during the design, it was also noticed that this would make it much easier to build the system mechanically, as it reduced the net forces across the chamber that are trying to force the torus towards the centre of the major axis. Ideally, the magnets surrounding the chamber should be more curved at the top and bottom and less on the inside and outsides in order to support these forces, which leads to something like an oval shape that the D closely approximated. The flatter shape on the inside edge was also easier to support due to the larger, flatter surface. While exploring the stability of various plasma shapes on a computer, the team noticed that non-circular plasmas did not exactly cancel out the vertical drift that the twisted fields have originally been introduced to solve. If the plasma was displaced up or down, it would continue travelling in that direction. However, the simulations demonstrated that the drift rate was slow enough that it could be counteracted using additional magnets and an electronic feedback system. The primary magnetic field in a tokamak is supplied by a series of magnets ringing the vacuum chamber. In JET, these are a series of 32 copper-wound magnets, each one weighing 12 tonnes. In total, they carry a current of 51 MA, and as they had to do so for periods of tens of seconds, they are water cooled. When operating, the coil is attempting to expand with a force of 6 MN, there is a net field towards the centre of the major axis of 20 MN, and a further twisting force because the poloidal field inside the plasma is in different directions on the top and bottom. All of these forces are borne on the external structure. Surrounding the entire assembly is the 2,600 tonne eight-limbed transformer which is used to induce a current into the plasma. The primary purpose of this current is to generate a poloidal field that mixes with the one supplied by the toroidal magnets to produce the twisted field inside the plasma. The current also serves the secondary purpose of ionizing the fuel and providing some heating of the plasma before other systems take over. The main source of heating in JET is provided by two systems, positive ion neutral beam injection and ion cyclotron resonance heating. The former uses small
particle accelerator A particle accelerator is a machine that uses electromagnetic fields to propel charged particles to very high speeds and energies, and to contain them in well-defined beams. Large accelerators are used for fundamental research in particle ...
s to shoot fuel atoms into the plasma, where collisions cause the atoms to ionize and become trapped with the rest of the fuel. These collisions deposit the kinetic energy of the accelerators into the plasma. Ion cyclotron resonance heating is essentially the plasma equivalent of a
microwave oven A microwave oven (commonly referred to as a microwave) is an electric oven that heats and cooks food by exposing it to electromagnetic radiation in the microwave frequency range. This induces polar molecules in the food to rotate and produce ...
, using
radio wave Radio waves are a type of electromagnetic radiation with the longest wavelengths in the electromagnetic spectrum, typically with frequencies of 300 gigahertz (GHz) and below. At 300 GHz, the corresponding wavelength is 1 mm (shor ...
s to pump energy into the ions directly by matching their
cyclotron frequency Cyclotron resonance describes the interaction of external forces with charged particles experiencing a magnetic field, thus already moving on a circular path. It is named after the cyclotron, a cyclic particle accelerator that utilizes an oscillati ...
. JET was designed so it would initially be built with a few megawatts of both sources, and then later be expanded to as much of 25 MW of neutral beams and 15 MW of cyclotron heating. 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, roughly the same amount of kinetic energy as a train weighing 5,000 tons traveling at . Each flywheel uses 8.8 MW to spin up and can generate 400 MW (briefly).


See also

*
Fusion power Fusion power is a proposed form of power generation that would generate electricity by using heat from nuclear fusion reactions. In a fusion process, two lighter atomic nuclei combine to form a heavier nucleus, while releasing energy. Devices de ...


References


Bibliography

* * *


External links

*
JET pages on the EURO''fusion'' web site
*
Poloidal field coils
diagram *
JET demonstrates alpha particle heating. Oct 2005
good graph
Culham Centre for Fusion Energy

The United Kingdom Atomic Energy Authority



Photos from JET Torus Hall


Sources




T. Fujita, et al., "High performance experiments in JT-60U reversed shear discharges", ''Nuclear Fusion'', Vol 39, p. 1627 (1999)
{{authority control Joint undertakings of the European Union and European Atomic Energy Community Culham Centre for Fusion Energy Tokamaks Energy in the European Union International science experiments