Jump to content

Joint European Torus

Coordinates:51°39′33″N1°13′35″W/ 51.65917°N 1.22639°W/51.65917; -1.22639
From Wikipedia, the free encyclopedia

JET
Joint European Torus
JET in 1991
Device typeTokamak
LocationOxfordshire,UK
AffiliationCulham Centre for Fusion Energy
Technical specifications
Major radius2.96 m (9 ft 9 in)
Minor radius1.25 m (4 ft 1 in)
Plasma volume100m3
Magnetic field3.45 T (34,500 G) (toroidal)
Heating power38MW
Plasma current3.2MA(circular),
4.8MA(D-shape)
History
Year(s) of operation1983–2023

TheJoint European Torus(JET) was amagnetically confinedplasma physicsexperiment, located atCulham Centre for Fusion EnergyinOxfordshire,UK.Based on atokamakdesign, the fusion research facility was a joint European project with the main purpose of opening the way to futurenuclear fusiongrid energy. At the time of its design JET was larger than any comparable machine.

JET was built with the hope of reachingscientific breakevenwhere thefusion energy gain factorQ=1.0.[1]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 includingtritiumwere made, making JET the first reactor in the world to run on the production fuel mix of 50–50 tritium anddeuterium.It was also decided to add adivertordesign 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, reachingQ= 0.67 in 1997, producing 16 MW of fusion power while injecting 24 MW of thermal power to heat the fuel.[2]

Between 2009 and 2011, JET was shut down to rebuild many of its parts, to adopt concepts being used in the development of theITERproject inSaint-Paul-lès-Durance,inProvence,southern France.[3]In December 2020, a JET upgrade commenced using tritium, as part of its contribution to ITER.[4]

Immediately after the announcement of JET's closure at the IAEA conference in London, October 2023, the group "Scientists for JET" launched a petition to call for a review of the decision to close JET, with scientists fearing a research time gap and personnel loss between JET's closure and the start of ITER's operations.[5]

JET finished operations in December 2023, with decommissioning expected to last until 2040.[6]

History

[edit]

Background

[edit]

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 at theBohm diffusionlimit, far below what would be needed for a practical fusion generator.[7]

In 1968, the Soviets held the periodic meeting of fusion researchers inNovosibirsk,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.[8][9]

A key issue in tokamak designs was that they did not generate enough of an electric current in theirplasmato 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, thePrinceton Large Torus(PLT) demonstrated thatneutral beam injectionwas a workable concept, using it to reach record temperatures well over the 50 million K that is the minimum needed for a practical reactor.[10]

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 withsuperconductingmagnets and vacuum vessels that could holddeuterium-tritiumfuel instead of the test fuels containing pure deuterium orhydrogenthat had been used up to that point.[11]

European design

[edit]
Design of JET

In 1971, the member states of theEuropean Atomic Energy Community(Euratom) decided in favour of a robust fusion programme and provided the necessary legal framework for a European fusion device to be developed.[12]In 1975, the first proposals for the JET machine were completed. Detailed design took three years.[13]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.[14]

The reactor was built at a new site next to theCulham Centre for Fusion Energy,the UK's fusion research laboratory which opened in 1965. The construction of the buildings was undertaken byTarmac Construction,[15]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.[14]The cost was 198.8 Million European Units of Account (predecessor to the Euro)[16]or 438 million in 2014 US dollars.[17]

JET was one of only two tokamak models designed to work with a realdeuterium-tritiumfuel mix, the other being the US-builtTFTR.Both were built with the hope of reachingscientific breakevenwhere the "fusion energy gain factor" orQ= 1.0.[18][19][20][1]

JET achieved its first plasma on 25 June 1983.[14]It was officially opened on 9 April 1984 byQueen Elizabeth II.[21]On 9 November 1991, JET performed the world's first deuterium-tritium experiment.[22]This beat the US's machine, TFTR, by a full two years.[23]

Upgrades

[edit]

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 effortITER.[24]

In 1991, the first experiments includingtritiumwere made, allowing JET to run on the production fuel of a 50–50 mix of tritium anddeuterium.[3]It was also decided at this time to add a divertor, allowing removal of waste material from the plasma.[25]Performance was significantly improved, allowing JET to set many records in terms of confinement time, temperature andfusion triple product.In 1997, JET set the record for the closest approach to scientific breakeven. It attainedQ= 0.67, producing 16 MW of fusion energy while injecting 24 MW of thermal power to heat the fuel,[26]a record that endured until 2021.[27][28]This was also the record for greatest fusion power produced.[29][30]

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 theInternational Thermonuclear Experimental Reactor(ITER) being developed atSaint-Paul-lès-Durance,inProvence,southern France. This Remote Handling system was later to lead on to becomeRACE (Remote Applications in Challenging Environments).[31]

In 1999, theEuropean Fusion Development Agreement(EFDA) was established with responsibility for the future collective use of JET.[32]

ITER design work

[edit]

In October 2009, a 15-month shutdown period was started to rebuild many parts of the JET to adopt concepts being used in the development of theITERproject inSaint-Paul-lès-Durance,inProvence,southern France.[3]This including replacingcarboncomponents in the vacuum vessel withtungstenandberylliumones.[33]

In mid-May 2011, the shutdown reached its end.[34]The first experimental campaign after the installation of the "ITER-Like Wall" started on 2 September 2011.[35]

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.[36]

Post-Brexit

[edit]

Brexitthrew 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.[37]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.[12]However, in March 2019, the UK Government and European Commission signed a contract extension for JET.[38]This guaranteedJEToperations until the end of 2024 regardless of Brexit situation.[39]In December 2020, a JET upgrade commenced using tritium, as part of its contribution to ITER.[4]

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.[28][40]

In October 2023, JET set its final fusion energy record, producing 69.29 megajoules over 6 seconds from only 0.21 mg ofD-Tfuel.[41][42]In November 2023, a petition asking that JET not be closed was started, with scientists fearing a research time gap and personnel loss between JET's closure and the start of ITER's operations.[5]Operations ceased in December, after performing 105,842 pulses, with decommissioning expected to last until 2040.[6]The final pulses were used to operate JET outside of its design capabilities.[43]The decommissioning and repurposing process is expected to last until 2040.[6]

Petition against the closure of JET

[edit]

Immediately after the announcement of JET's closure at the IAEA conference in London, October 2023, the group "Scientists for JET" launched a petition to call for a review of the decision to close JET. [5]The scientists are concerned that JET's end date was set assuming thatITERwould be up and running by that date to continue fusion experiments, but with ITER's startup being postponed and ITER's deuterium-tritium (D-T) reactions only scheduled for 2035, that there will be a gap of many years with no fusion research.[5]

Description

[edit]
Internal view of the JET tokamak superimposed with an image of a plasma taken with avisible spectrumvideo camera.

JET has a major radius of 3 metres, and the D-shaped vacuum chamber is 2.5 metres wide and 4.2 metres high.[44]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.[45]

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.[46]

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.[44]

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 6MN,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.[47]

Surrounding the entire assembly is the 2,600 tonne eight-limbed transformer which is used toinducea 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.[48]

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 smallparticle acceleratorsto 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 amicrowave oven,usingradio wavesto pump energy into the ions directly by matching theircyclotron frequency.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.[49]

JET's power requirements during the plasma pulse are around 500 MW[50]with peak in excess of 1000 MW.[51]Because power draw from the main grid is limited to 575 MW, two largeflywheel generatorswere constructed to provide this necessary power.[51]Each 775-ton flywheel can spin up to 225 rpm and store 3.75 GJ,[52]roughly the same amount of kinetic energy as a train weighing 5,000 tons traveling at 140 kilometres per hour (87 mph). Each flywheel uses 8.8 MW to spin up and can generate 400 MW (briefly).[51]

See also

[edit]

References

[edit]
  1. ^ab"Design Specification".European Union. 29 February 2008. p. 28.Retrieved18 July2020.
  2. ^"History of Fusion".EUROfusion.14 December 2017.Retrieved10 February2022.
  3. ^abc"Joint European Torus".Culham Centre Fusion Energy.Retrieved18 July2020.
  4. ^abGibney, Elizabeth (22 February 2021)."Fuel for world's largest fusion reactor ITER is set for test run".Nature.591(7848): 15–16.Bibcode:2021Natur.591...15G.doi:10.1038/d41586-021-00408-1.PMID33619399.
  5. ^abcdStarckx, Senne (1 November 2023)."Petition calls on UK to save JET fusion experiment from closure".Physics World, Institute of Physics.Retrieved28 December2023.
  6. ^abcCrepaz, Leah (20 December 2023)."Pioneering JET delivers final plasma".UK Atomic Energy Authority.Retrieved20 December2023.
  7. ^Bromberg 1982,pp. 130–131.
  8. ^Bromberg 1982,pp. 151.
  9. ^Kenward 1979,p. 627.
  10. ^Kenward 1979,p. 628.
  11. ^Kenward 1979,p. 630.
  12. ^abStefanini, Sara (7 April 2017)."Brexit brings nuclear (con)fusion".
  13. ^Rebut, Paul-Henri."JET's first plasma".Archived fromthe originalon 17 December 2022.Retrieved14 December2017.
  14. ^abc"About JET's startup".EUROfusion.Archived fromthe originalon 17 December 2022.Retrieved9 December2015.
  15. ^Berry Ritchie,The Story of Tarmacp. 100, Published by James & James (Publishers) Ltd, 1999
  16. ^"You searched for cost – EUROfusion".EUROfusion.Retrieved9 December2015.
  17. ^"Measuring Worth - Results".Archived fromthe originalon 23 May 2013.Retrieved9 December2015.
  18. ^Wesson 1999,p. 25.
  19. ^"THE JET PROJECT: Design Proposal for the Joint European Torus".1976. p. 25.
  20. ^"The JET Project"(PDF).1975. p. 17.
  21. ^"The Opening of JET 1984".EUROfusion.Archived fromthe originalon 17 December 2022.Retrieved26 June2016.
  22. ^Rebut, P-H (1992). "The JET preliminary tritium experiment".Plasma Physics and Controlled Fusion.34(13): 1749–1758.Bibcode:1992PPCF...34.1749R.doi:10.1088/0741-3335/34/13/002.S2CID250880054.
  23. ^"Celebrating the 20th anniversary of the tritium shot heard around the world".PPPL.9 December 2013. Archived fromthe originalon 17 December 2022.Retrieved14 December2017.
  24. ^The ITER project.EFDA, European Fusion Development Agreement (2006).
  25. ^"Re-tiling a fusion reactor".Eureka. 5 September 2018.Retrieved18 July2020.
  26. ^"Milestones around the world".ITER.
  27. ^Clery, Daniel (17 August 2021)."With explosive new result, laser-powered fusion effort nears 'ignition'".Science.AAAS.
  28. ^abGibney, Elizabeth (9 February 2022)."Nuclear-fusion reactor smashes energy record".Nature.602(7897): 371.Bibcode:2022Natur.602..371G.doi:10.1038/d41586-022-00391-1.PMID35140372.S2CID246701390.
  29. ^"JET".Culham Centre for Fusion Energy.Archived fromthe originalon 7 July 2016.Retrieved12 December2017.
  30. ^"JET".Culham Centre Fusion Energy. Archived fromthe originalon 7 July 2016.Retrieved26 June2016.
  31. ^"How we do Remote Handling at JET?".EUROfusion.Archived fromthe originalon 17 December 2022.Retrieved26 June2016.
  32. ^"What is EFDA"(PDF).Seccio D'Enginyeria Nuclear. Archived fromthe original(PDF)on 17 August 2016.Retrieved26 June2016.
  33. ^"The ITER-like Wall Project at JET".EUROfusion.Archived fromthe originalon 17 December 2022.Retrieved26 June2016.
  34. ^"JET Shutdown Weekly: Week 81: Shutdown finished!".EUROfusion.13 May 2011. Archived fromthe originalon 15 April 2012.Retrieved11 December2011.
  35. ^"World's largest fusion experiment back in operation".EUROfusion.2 September 2011. Archived fromthe originalon 15 April 2012.Retrieved11 December2011.
  36. ^"Contract for Joint European Torus signed".Horizon 2000 projects.Retrieved14 July2014.
  37. ^"EUROfusion and UK after Brexit".EUROfusion.Archived fromthe originalon 17 December 2022.Retrieved26 June2016.
  38. ^"Future of JET secured with new European contract".GOV.UK.Retrieved11 July2019.
  39. ^"Nuclear research if there's no Brexit deal".GOV.UK.Retrieved11 July2019.
  40. ^"European researchers achieve fusion energy record".euro-fusion.org.9 February 2022.Retrieved9 February2022.
  41. ^Tischler, Karl (8 February 2024)."Breaking New Ground: JET Tokamak's Latest Fusion Energy Record Shows Mastery of Fusion Processes".EUROfusion.Retrieved11 February2024.
  42. ^"UK's nuclear fusion site ends experiments after 40 years".13 October 2023 – via bbc.co.uk.
  43. ^"JET's final plasma programme was a challenging one, creating a plasma shape with a ꓷ rather than the traditional D, something which had never been attempted before".UK Atomic Energy Authority. 20 December 2023.Retrieved20 December2023.
  44. ^abWesson 1999,p. 26.
  45. ^Wesson 1999,p. 21.
  46. ^Wesson 1999,p. 22.
  47. ^Wesson 1999,p. 31.
  48. ^Wesson 1999,p. 32.
  49. ^Wesson 1999,pp. 32–33.
  50. ^"775 tons of steel".EUROfusion.Archived fromthe originalon 17 December 2022.Retrieved9 December2015.
  51. ^abc"Power supply".EUROfusion.Archived fromthe originalon 5 January 2016.Retrieved9 December2015.
  52. ^"Week 20: JET Experiments: sensitive to TV schedules".EUROfusion.Archived fromthe originalon 2 February 2014.Retrieved26 June2016.

Bibliography

[edit]
[edit]

Sources

[edit]

51°39′33″N1°13′35″W/ 51.65917°N 1.22639°W/51.65917; -1.22639

Retrieved from "https://en.wikipedia.org/w/index.php?title=Joint_European_Torus&oldid=1231059426"