View source for JT-60

{{Short description|Japanese tokamak}}
{{about|the tokamak|the school district|Miami-Yoder School District JT-60}}
{{More science citations needed|date=April 2025}}
{{stack begin}}
{{Infobox fusion device
|name                 = JT-60
|fullname             = Japan Torus-60
|image                =
|imagetitle           =
|type                 = [[Tokamak]]
|city                 = [[Naka, Ibaraki|Naka]]
|state                = [[Ibaraki Prefecture]]
|country              = [[Japan]]
|coordinates          = <!-- {{coord|latitude|longitude|type:city|display=inline,title}} -->
|affiliation          = [[Japan Atomic Energy Agency]]
|major_radius         = {{cvt|3.4|m}}
|minor_radius         = {{cvt|1.0|m}}
|volume               = {{val|90|ul=m3}}
|field                = {{cvt|4|T}} (toroidal)
|heating              =
|temperature          =
|power                =
|time                 = {{val|65|ul=s}}
|current              =
|construction_date    =
|operation_start_year = 1985
|operation_end_year   = 2010
|ongoing              =
|prev                 = [[JAERI Fusion Torus-2M|JFT-2M]]
|next                 = JT-60SA
|related              = [[Tokamak Fusion Test Reactor|TFTR]]
|website              = {{URL|https://www.qst.go.jp/site/jt60-english/}}
|other_links          =
}}
{{Infobox fusion device
|name                 = JT-60SA
|fullname             = Japan Torus-60 Super Advanced
|image                =
|imagetitle           = A front view of JT-60SA in 2023
|type                 = [[Tokamak]]
|city                 = [[Naka, Ibaraki|Naka]]
|state                = [[Ibaraki Prefecture]]
|country              = [[Japan]]
|coordinates          = <!-- {{coord|latitude|longitude|type:city|display=inline,title}} -->
|affiliation          = [[National Institute of Radiological Sciences|QST]] + [[Fusion for Energy|F4E]]
|major_radius         = <!-- {{cvt|3.4|m}} -->
|minor_radius         = <!-- {{cvt|1.0|m}} -->
|volume               = <!-- {{val|90|ul=m3}} -->
|field                = <!-- {{cvt|4|T}} (toroidal) -->
|heating              =
|temperature          =
|power                =
|time                 = {{val|100|u=s}}
|current              =
|construction_date    = 2013–2020
|operation_start_year = 2023
|operation_end_year   = 
|ongoing              = yes
|prev                 = JT-60U
|next                 = 
|related              = [[ITER]]
|website              = {{URL|https://www.jt60sa.org/wp/}}
|other_links          =
}}
{{stack end}}
'''JT-60''' (short for '''Japan Torus-60''') is a large research [[tokamak]], the flagship of the [[Japan]]ese [[National Institute of Radiological Sciences|National Institute for Quantum Science and Technology]]'s [[Fusion power|fusion energy]] directorate. As of 2023 the device is known as '''JT-60SA''' and is the largest operational [[Superconductivity|superconducting]] tokamak in the world,<ref name="first">{{cite web |date=24 October 2023 |title=First plasma 23 October |url=https://www.jt60sa.org/wp/first-plasma-23-october/ |url-status=live |archive-url=https://web.archive.org/web/20231027211642/https://www.jt60sa.org/wp/first-plasma-23-october/ |archive-date=27 October 2023 |access-date=15 November 2023 |website=JT-60SA}}</ref> built and operated jointly by the [[European Union]] and Japan in [[Naka, Ibaraki|Naka]], [[Ibaraki Prefecture]].<ref name="JT-60SA">{{cite web |title=What is JT-60SA? |url=https://www.jt60sa.org/wp/ |url-status=live |archive-url=https://web.archive.org/web/20231115015432/https://www.jt60sa.org/wp/ |archive-date=15 November 2023 |access-date=15 November 2023 |website=JT-60SA}}</ref><ref>{{cite web |title=Naka Fusion Institute |url=http://www.naka.jaea.go.jp/english/NAKA-HPe.html |url-status=dead |archive-url=https://web.archive.org/web/20070701014102/http://www.naka.jaea.go.jp/english/NAKA-HPe.html |archive-date=1 July 2007 |access-date=14 January 2022 |website=www.naka.jaea.go.jp}}</ref> SA stands for super [[Tokamak#Advanced tokamaks|advanced tokamak]], including a D-shaped [[Plasma (physics)|plasma]] [[Cross section (geometry)|cross-section]], superconducting coils, and active feedback control.

JT-60 claimed that it held the record{{efn|name=dispute|Disputed; see [[#JT-60/TFTR disputed records|below]]}} for the highest value of the [[Lawson criterion|fusion triple product]] achieved: {{val|1.77|e=28|u=[[kelvin|K]]·[[second|s]]·m<sup>−3</sup>}} = {{val|1.53|e=21|u=[[electronvolt|keV]]·s·m<sup>−3</sup>}}.<ref name="jt60site">{{cite web |title=JT-60 HOME PAGE |url=https://www-jt60.naka.qst.go.jp/english/jt60/project/html/history.html |access-date=25 April 2021 |publisher=[[Japan Atomic Energy Agency]] |archive-date=25 April 2021 |archive-url=https://web.archive.org/web/20210425150601/https://www-jt60.naka.qst.go.jp/english/jt60/project/html/history.html |url-status=live }}</ref><ref name="JT-60-history">[http://www-jt60.naka.jaea.go.jp/english/jt60/project/html/history.html JT-60 Operational History and the Progress of Plasma Performance] {{webarchive|url=https://web.archive.org/web/20160223140234/http://www-jt60.naka.jaea.go.jp/english/jt60/project/html/history.html|date=2016-02-23}}</ref> The product quoted is not a valid fusion triple product since the plasmas did not satisfy the steady state of the [[Lawson criterion]] as discussed below.  

JT-60 also claimed without proof that it held the record{{efn|name=dispute}} for the hottest ion temperature ever achieved (522 megakelvins). In reality the [[Tokamak Fusion Test Reactor|TFTR]] machine at [[Princeton Plasma Physics Laboratory|Princeton]] routinely measured higher ion temperatures during the 1993-1996 campaign, as discussed below.<ref name="jaea">{{Cite web |title=Plasma physics found in JT-60 tokamak over the last 20 years |url=https://jopss.jaea.go.jp/search/servlet/search?5017810&language=1 |access-date=2020-12-19 |archive-date=2021-01-21 |archive-url=https://web.archive.org/web/20210121220058/https://jopss.jaea.go.jp/search/servlet/search?5017810&language=1 |url-status=live }}</ref>

==Original design==
JT-60 was first designed in the 1970s during a period of increased interest in nuclear fusion from major world powers. In particular, the [[United States|US]], [[United Kingdom|UK]] and Japan were motivated by the excellent performance of the Soviet T-3 in 1968 to further advance the field. The [[Japan Atomic Energy Agency|Japanese Atomic Energy Research Institute]] (JAERI), previously dedicated to fission research since 1956, allocated efforts to fusion.

JT-60 began operations on April 8, 1985,<ref>{{Cite report|author1=核融合研究センター |date=1986 |title=Annual Report of the Fusion Research Center for the Period of April 1, 1984 to March 31, 1985 |language=ja |publisher=日本原子力研究開発機構 |doi=10.11484/jaeri-m-85-205}}</ref> and demonstrated performance far below predictions, much like the TFTR and JET that had begun operations shortly prior.

Over the next two decades, TFTR, JET and JT-60 led the effort to regain the performance originally expected of these machines. JT-60 underwent a major modification during this time, '''JT-60U''' (for "upgrade") in March 1991.<ref>{{cite book|title=FUSION - Future Energy of the Earth|author=Naka Fusion Institute|publisher=Japan Atomic Energy Agency|page=12|date=June 2008|access-date=25 January 2024|url=https://www.qst.go.jp/uploaded/attachment/5304.pdf|archive-date=17 August 2022|archive-url=https://web.archive.org/web/20220817202150/https://www.qst.go.jp/uploaded/attachment/5304.pdf|url-status=live}}</ref> The change resulted in significant improvements in plasma performance.

===JT-60/TFTR disputed records===
{{Disputed section|date=April 2025}}
By 1996, JT-60 had achieved its record ion temperature of 45 keV,<ref name="jaea" /> which is claimed to have exceeded the highest temperatures measured at that time in the [[TFTR]] [[tokamak]] in Princeton. Detailed measurements of the ion temperatures analyzed during TFTR's experimental campaign with deuterium-tritium plasmas in 1993–1996, found numerious discharges with temperatures greater than 50 keV in both deuterium-only and deuterium-tritium plasmas.<ref name="budny-2025" /> A 2025 publication of a reanalysis of TFTR transport and confinement results for a selected scan of discharges mentions that several "supershots", not in the scan, had ion temperatures of 70 keV with a measurement error bar of 28%.<ref name="budny-2025">{{cite journal|last1=Budny|first1=R.V.|last2=Fredrickson|first2=E.|last3=Skinner|first3=C.H.|url=https://iopscience.iop.org/article/10.1088/1741-4326/adbe8f|title=Isotopic mass effects of tritium-fueled high-performance TFTR supershots|date=2025|journal=[[Nuclear Fusion (journal)|Nuclear Fusion]]|publisher=[[IOP Publishing]]|volume=65|issue=5|doi=10.1088/1741-4326/adbe8f|bibcode=2025NucFu..65e6005B |doi-access=free}}</ref> 

The TFTR team did not highlight these high temperatures for several reasons. The ion temperature measurements in JT-60, TFTR, and JET measured only singly ionized trace carbon impurity ions, not the temperatures of the hydrogenic ions. The carbon ions do not fuse, and displace the deuterium and tritium ions which can fuse. The hydrogenic ion temperatures can be calculated in the [[TRANSP]] analysis code. The methods used are published and widely used in analysis of experimental results.
<ref>'Simulations of deuterium-tritium experiments in TFTR'
R.V. Budny,et al.
Nuclear Fus. Vol 32 (1992) p 429-447
cphttps://iopscience.iop.org/article/10.1088/0029-5515/32/3/I07/pdf</ref> These temperatures are the relevant ones for calculating the deuterium and tritium fusion reactions. They generally are less than the carbon temperatures. Secondly, the end goal of this research, practical minimally poluting fusion energy, does not require ion temperatures greater than about 25 keV.
An example of simulation of a burning plasma in [[ITER]] is
<ref> "Predictions of H-mode performance in ITER", R. V. Budny,
R. Andre, G. Bateman, F. Halpern, C.E. Kessel, A. Kritz and D. McCune
Nuclear Fus. (2008) <48> 075005
https://iopscience.iop.org/article/10.1088/0029-5515/48/7/075005</ref>

The fusion triple product metric applies only to plasmas in steady state, as stated explicitly in the [[Lawson criterion]]. The JT-60 plasmas with high values were far from steady state; in fact, their conditions rose rapidly in time to those values, and then suffered major disruptions, which extinguished the plasmas abruptly. Examples are in.
<ref>Achievement of High Fusion Performance in JT-60U Reversed Shear Discharges S. Ishida, et al. 1997 Physical Review Letters 79 3917</ref> 
<ref>HIGH PERFORMANCE EXPERIMENTS IN JT-60U
REVERSED SHEAR DISCHARGES T. FUJITA, et al. 
IAEA-CN-69/EX1/2</ref>
Also the derivation of the fusion triple product assumes that the fusion power results from thermonuclear fusion (from thermal deuterium and tritium). Instead the high fusion power in past tokamak experiments resulted dominatly from beam-thermal reactions.

Thus the JT-60's claimed record for the triple product is not a 'fusion triple product'. Steady state discharges have been achieved in other devices such as Tore Supra and [[WEST (formerly Tore Supra)|WEST]] have announced results for the fusion triple product.<ref>{{cite journal|last1=Wurzel|first1=Samuel E.|last2=Hsu|first2=Scott C.|url=https://pubs.aip.org/aip/pop/article/29/6/062103/2847827/Progress-toward-fusion-energy-breakeven-and-gain|title=Progress toward fusion energy breakeven and gain as measured against the Lawson criterion|date=2022|journal=[[Physics of Plasmas]]|volume=29|issue=62103|doi=10.1063/5.0083990|arxiv=2105.10954|bibcode=2022PhPl...29f2103W }}</ref>

==JT-60U (Upgrade)==
The main objective of the JT-60U upgrade was to "investigate energy confinement near the breakeven condition, [a] non-inductive current drive and burning plasma physics with [[deuterium]] plasmas." To accomplish this, the poloidal field coils and the vacuum vessel were replaced. Construction began in November 1989 and was completed in March 1991.<ref>{{Cite report|title=Annual report of the Naka Fusion Research Establishment for the period of April 1, 1990 to March 31, 1991 |date=1991 |language=ja |doi=10.11484/jaeri-m-91-159 |author1=那珂研究所 |publisher=日本原子力研究開発機構 }}</ref> Operations began in July.<ref>{{Cite report|title=Annual report of Naka Fusion Research Establishment for the period of April 1, 1991 to March 31, 1992 |date=1992 |language=ja |doi=10.11484/jaeri-m-92-159 |author1=那珂研究所 |publisher=日本原子力研究開発機構 }}</ref>

JT-60U researchers claimed that on October 31, 1996, they achieved an estimated breakeven factor of ''Q''{{sub|DT}}{{sup|eq}} = 1.05 at {{val|2.8|u=MA}}.<ref>{{cite web|url=https://www.qst.go.jp/site/jt60-english/5586.html|title=JT-60U Experimental Report No. 39 (November 11, 1996): JT-60U Achieved Optimized Negative Magnetic Shear Discharges with QDT > 1|work=[[National Institutes for Quantum and Radiological Science and Technology|QST]]|date=26 December 2018|access-date=22 April 2025}}</ref> In other words, if the [[Homogeneity and heterogeneity|homogenous]] deuterium fuel was theoretically replaced with a 1:1 mix of deuterium and [[tritium]], the fusion reaction is estimated to have created an energy output 1.05 times the energy injected into the tokamak. An estimate based on a discharge in 1968 gave  
''Q''{{sub|DT}}{{sup|eq}} = 1.25.<ref>High performance experiments in JT-60U reversed shear discharges
T. Fujita, 1999  Nucl. Fusion 39 1627
DOI 10.1088/0029-5515/39/11Y/302</ref> The record of the central ratio Q{{sub|core}} achieved in a tokamak discharge is 1.3 in JET in 1998.
<ref>"Core fusion power gain and alpha heating in JET, TFTR, and ITER",
R.V. Budny, J.G. Cordey and TFTR Team and JET Contributors,
Nuclear Fus. (2016) <56> 056002 #5 (May)
https://iopscience.iop.org/article/10.1088/0029-5515/56/5/056002
//home/budny/papers/NF/core_q_dt/nf_56_5_056002.pdf</ref>

A credible estimate of extrapolation of a deuterium plasma to a deuterium-tritium plasma requires starting with a validated and verified integrated computer model, and then reruning with a deuterium-tritium mixture to calculate the fusion yield. Details of the deuterium plasma also need to be shown for credibility. An example of such an estimate was published before [[TFTR]] started its deuterium-tritium campaign in 1993–1996.<ref> Simulations of deuterium–tritium experiments in TFTR Budny R.V. et al 1992 Nucl. Fusion 32 429
DOI 10.1088/0029-5515/32/3/I07</ref> This paper calculated that the ''Q''{{sub|DT}}{{sup|eq}} would be 0.32. In retrospect, the record achieved was 0.28 (discharge 80539) so the projection were optimistic. A much larger amount of energy was injected into the TFTR and JT-60U test chambers. JT-60U was not equipped to utilize tritium, as it would add extensive costs and safety risks.{{efn|The JT-60 team submitted data for more than ten of its best discharges to the PPPL [[Princeton Plasma Physics Laboratory]] for analysis with its [[TRANSP]] code for analysis and extrapolation to a hypothetical mix of deuterium and tritium fuel. The results are archived at PPPL. The submitted data were not sufficient for credible modeling since they lacked data for the profile of the impurities, which would dilute the deuterium and tritium.{{citation needed|date=April 2025}}<!-- please do not remove this tag before adding a citation --> The TRANSP modeling over estimated the measured fusion rate by a wide margin. Also the data set did not include a sufficient number of time steps needed for accuracy.{{citation needed|date=April 2025}}<!-- please do not remove this tag before adding a citation -->}}

In February 1997, a modification to the [[divertor]] from an open-type shape to a semi-closed W-shape for greater particle and impurity control was started and later completed in May.<ref>{{cite report|title=Annual Report from April 1, 1996 to March 31, 1997|author1=Naka-machi|author2=Naka-gun|author3=Ibaraki-ken|publisher=Naka Fusion Research Establishment|url=https://www.qst.go.jp/uploaded/attachment/7664.pdf|page=1|year=1997|access-date=26 January 2024|quote=The construction for the divertor modification from the original open type to the W-shaped semi-closed type for improving the particle control was started on February 1997.|archive-date=January 16, 2024|archive-url=https://web.archive.org/web/20240116114000/https://www.qst.go.jp/uploaded/attachment/7664.pdf|url-status=live}}</ref><ref>{{cite report|title=Annual Report of Naka Fusion Research Establishment from April 1, 1997 to March 31, 1998|author1=Naka-machi|author2=Naka-gun|author3=Ibaraki-ken|publisher=|url=https://www.qst.go.jp/uploaded/attachment/7665.pdf|page=1|date=1 October 1998|access-date=26 January 2024|quote=The construction for the divertor modification from the original open type to the W-shaped semi-closed type for improving the particle control was finished in May 1997.|archive-date=16 January 2024|archive-url=https://web.archive.org/web/20240116113958/https://www.qst.go.jp/uploaded/attachment/7665.pdf|url-status=live}}</ref><ref>{{Cite book|author1=Olgierd Dumbrajs|author2=Jukka Heikkinen|author3=Seppo Karttunen|author4=T. Kiviniemi|author5=Taina Kurki-Suonio|author6=M. Mantsinen|author7=Timo Pättikangas|author8=K.M. Rantamäki|author9=Ralf Salomaa|author10=Seppo Sipilä|title=Local current profile modification in tokamak reactors in various radiofrequency ranges|series=Publication / Division of Scientific and Technical Information, International Atomic Energy Agency|date=1997|isbn=978-92-0-103997-2|url=https://cris.vtt.fi/en/publications/local-current-profile-modification-in-tokamak-reactors-in-various|publisher=International Atomic Energy Agency IAEA|location=Vienna|access-date=2024-02-25|archive-date=2023-10-22|archive-url=https://web.archive.org/web/20231022110906/https://cris.vtt.fi/en/publications/local-current-profile-modification-in-tokamak-reactors-in-various|url-status=live}}</ref> Experiments simulating the [[helium]] exhaust in ITER were promptly performed with the modified divertor, with great success. In 1998, the modification allowed JT-60U to reach an estimated fusion energy gain factor of ''Q''{{sub|DT}}{{sup|eq}} = 1.25 at {{val|2.6|u=MA}},<ref>{{cite web |date=7 August 1998 |title=JT-60U Reaches 1.25 of Equivalent Fusion Power Gain |url=http://www-jt60.naka.jaea.go.jp/english/html/exp_rep/rep46.html |archive-url=https://web.archive.org/web/20130106002827/http://www-jt60.naka.jaea.go.jp/english/html/exp_rep/rep46.html |archive-date=6 January 2013 |access-date=5 December 2016}}</ref><ref>{{Cite book |last=Clery |first=Daniel |url=https://books.google.com/books?id=EGcjCQAAQBAJ&dq=JT-60U+q=1.2&pg=PT103 |title=A Piece of the Sun: The Quest for Fusion Energy |date=2014-07-29 |publisher=Overlook Press |isbn=978-1-4683-1041-2 |language=en |access-date=2024-02-02 |archive-date=2024-02-25 |archive-url=https://web.archive.org/web/20240225031553/https://books.google.com/books?id=EGcjCQAAQBAJ&dq=JT-60U+q=1.2&pg=PT103 |url-status=live }}</ref><ref>{{Cite web |url=http://www-pub.iaea.org/mtcd/publications/pdf/csp_001c/pdf/ex1_2.pdf |title=HIGH PERFORMANCE EXPERIMENTS IN JT-60U REVERSED SHEAR DISCHARGES |access-date=2017-04-30 |archive-date=2017-03-09 |archive-url=https://web.archive.org/web/20170309175436/http://www-pub.iaea.org/MTCD/Publications/PDF/csp_001c/pdf/ex1_2.pdf |url-status=live }}</ref> as discussed above.

In December 1998, a modification to the vacuum pumping system that began in 1994 was completed. In particular, twelve [[turbomolecular pump]]s with oil [[Bearing (mechanical)|bearings]] and four oil sealed rotary vacuum pumps were replaced with [[Magnetic levitation|magnetically suspended]] turbomolecular pumps and dry vacuum pumps. The modification reduced the 15-year-old system's consumption of [[liquid nitrogen]] by two thirds.<ref>{{cite report|url=https://www.qst.go.jp/uploaded/attachment/7666.pdf|title=Annual Report of Naka Fusion Research Establishment from April 1, 1998 to March 31, 1999|access-date=January 30, 2024|archive-date=January 30, 2024|archive-url=https://web.archive.org/web/20240130185039/https://www.qst.go.jp/uploaded/attachment/7666.pdf|url-status=live}}</ref>

In [[fiscal year]] 2003, the plasma discharge duration of JT-60U was successfully extended from {{val|15|u=s}} to {{val|65|u=s}}.<ref>{{cite report|url=https://www.qst.go.jp/uploaded/attachment/7659.pdf|title=Annual Report of Naka Fusion Research Establishment from April 1, 2003 to March 31, 2004|access-date=January 30, 2024|archive-date=January 30, 2024|archive-url=https://web.archive.org/web/20240130163350/https://www.qst.go.jp/uploaded/attachment/7659.pdf|url-status=live}}</ref>

In 2005, ferritic steel (ferromagnet) tiles were installed in the vacuum vessel to correct the magnetic field structure and hence reduce the loss of fast ions.<ref name=long2006>{{cite press release |url=http://www.jaea.go.jp/english/news/p06052303/index.shtml |title=Achievement of long sustainment of a high-confinement, high-pressure plasma in JT-60 - A big step towards extended burn in ITER with the use of ferritic steel - |agency=[[Japan Atomic Energy Agency]] |date=9 May 2006 |access-date=5 December 2016 |archive-date=16 June 2019 |archive-url=https://web.archive.org/web/20190616174720/https://www.jaea.go.jp/english/news/p06052303/index.shtml |url-status=live }}</ref><ref>{{Cite web |url=http://www.jaea.go.jp/english/news/p06052303/all.jpg |title=ferromagnet diagrams |access-date=2016-02-16 |archive-date=2017-01-24 |archive-url=https://web.archive.org/web/20170124075518/http://www.jaea.go.jp/english/news/p06052303/all.jpg |url-status=live }}</ref> 
The JAEA used new parts in the JT-60, having improved its capability to hold the plasma in its powerful toroidal magnetic field.

Sometime in 2007-2008, in order to control plasma pressure at the [[pedestal region]] and to evaluate the effect of fuel on the self-organization structure of plasma, a [[Supersonic speed|supersonic]] [[molecular beam]] injection (SMBI) system was installed in JT-60U. The system's design was a collaboration between [[Cadarache]], [[French Alternative Energies and Atomic Energy Commission|CEA]], and JAEA.<ref>{{cite report |url=https://www.qst.go.jp/uploaded/attachment/7663.pdf |title=Annual Report of Fusion Research and Development Directorate of JAEA from April 1, 2007 to March 31, 2008 |date=20 October 1998 |page=18 |access-date=30 January 2024 |archive-date=30 January 2024 |archive-url=https://web.archive.org/web/20240130140015/https://www.qst.go.jp/uploaded/attachment/7663.pdf |url-status=live }}</ref>
''Q''{{sub|DT}}{{sup|eq}}
JT-60U ended operations on August 29, 2008.<ref>{{Cite report|title=Annual report of Fusion Research and Development Directorate of JAEA for FY2008 and FY2009 |date=2011 |language=ja |doi=10.11484/jaea-review-2011-009 |author1=核融合研究開発部門 |publisher=日本原子力研究開発機構 }}</ref>

==JT-60SA==
[[File:JT-60SA Tokamak.jpg|thumb|JT-60SA under construction in 2016.]]
JT-60SA is the successor to JT-60U, operating as a satellite to [[ITER]] as described by the [[Broader Approach Agreement]]. It is a fully superconducting tokamak with flexible components that can be adjusted to find optimized plasma configurations and address key physics issues.<ref>{{Cite web |title=Broader Approach agreement |url=http://www.iter.org/sci/iterandbeyond |access-date=2024-02-29 |website=ITER |date=13 November 2023 |language=en |archive-date=2024-02-07 |archive-url=https://web.archive.org/web/20240207025358/https://www.iter.org/sci/iterandbeyond |url-status=live }}</ref> Assembly began in January 2013 and was completed in March 2020. After a major [[short circuit]] during [[integrated commissioning]] in March 2021 necessitating lengthy repairs, it was declared active on December 1, 2023. The overall cost of its construction is estimated to be around {{Currency|560M|euro|fmt=gaps}}, adjusted for inflation.<ref>{{Cite web |title=JT-60SA is officially the most powerful Tokamak |date=December 2023 |url=https://fusionforenergy.europa.eu/news/jt-60sa-is-officially-the-most-powerful-tokamak |access-date=2024-02-21 |archive-date=2024-02-21 |archive-url=https://web.archive.org/web/20240221024928/https://fusionforenergy.europa.eu/news/jt-60sa-is-officially-the-most-powerful-tokamak/ |url-status=live }}</ref>

Weighing roughly {{convert|2600|ST}},<ref name=":0">{{Cite book |url=https://www.qst.go.jp/uploaded/attachment/20800.pdf |title=JT-60SA - Toward the Realization of Fusion Energy |date=January 2021 |page=3 |access-date=26 January 2024 |archive-url=https://web.archive.org/web/20220814003411/https://www.qst.go.jp/uploaded/attachment/20800.pdf |archive-date=14 August 2022 |url-status=live}}</ref> JT-60SA's superconducting magnet system includes 18 D-shaped [[Niobium–titanium|niobium-titanium]] toroidal field coils, a [[Niobium–tin|niobium-tin]] central [[solenoid]], and 12 equilibrium field coils.

===History===
The idea of an advanced tokamak, a tokamak utilizing superconducting coils, traces back to the early 1960's.<!-- https://apps.dtic.mil/sti/citations/AD0622614 --> The idea seemed very promising, but was not without its problems. Around January 1972, engineers at JAERI initiated an effort to further research the idea and try to solve its hurdles.<ref>{{Cite web |title=Superconducting Coils for a Fusion Reactor |url=https://jopss.jaea.go.jp/search/servlet/search?3021685&language=1 |url-status=live |archive-url=https://web.archive.org/web/20240222142442/https://jopss.jaea.go.jp/search/servlet/search?3021685&language=1 |archive-date=2024-02-22 |access-date=2024-02-22}}</ref> This initiative progressed in parallel with the development of JT-60,<ref>{{Citation |last=核融合研究部 |title=核融合研究部および大型トカマク開発部 年報; 昭和52年度 |date=1979 |publisher=日本原子力研究開発機構 |doi=10.11484/jaeri-m-8059|doi-access=free}}</ref> and by 1983-84 it was decided that it constituted its own experimental reactor: FER (Fusion Experimental Reactor).<ref>{{Cite report |title=核融合実験炉(FER)概念設計; 昭和59年度、60年度 |trans-title=Nuclear Fusion Experimental Reactor (FER) Conceptual design; Showa 59, 60 |author1=臨界プラズマ研究部 |date=1986 |publisher=日本原子力研究開発機構 |doi=10.11484/jaeri-m-86-134 |doi-access=free |language=ja}}</ref>

However, the JT-60U upgrade in 1991 demonstrated the significant flexibility of the JT-60 facilities and assembly site, so by January 1993 FER was designated as a modification to JT-60U and renamed JT-60SU (for Super Upgrade).<ref>{{Cite book |title=15th IEEE/NPSS Symposium on Fusion Engineering: October 11 - 15, 1993, Hyannis, Massachusetts |date=1993 |publisher=IEEE Service Center |isbn=978-0-7803-1412-2 |editor-last=Institute of Electrical and Electronics Engineers |location=Piscataway, NJ |editor-last2=IEEE Nuclear and Plasma Sciences Society}}</ref> <!-- explain advantages of JT-60SU over JT-60U here -->

In January 1996, a paper detailing the superconducting properties of [[Niobium aluminide|Nb{{sub|3}}Al]] composite wire and its fabrication process was published in the 16th International Cryogenic Engineering/Materials Conference journal.<ref>{{Cite book |last1=Haruyama |first1=T. |title=Proceedings of the Sixteenth International Cryogenic Engineering Conference/ International Cryogenic Materials Conference: Kitakyushu, Japan, 20-24 May 1996 |last2=Mitsui |first2=Takeo |last3=Yamafuji |first3=Kaoru |date=1997 |publisher=Elsevier |others=International Cryogenic Engineering Conference, International Cryogenic Materials Conference |isbn=978-0-08-042688-4 |location=Oxford}}</ref> Engineers assessed the potential use of the [[aluminide]] in JT-60SU's 18 toroidal coils.<ref>{{Cite report|title=定常炉心試験装置の設計研究,第5編; 電源設備|trans-title=Design and research of constant furnace core test device, Part 5; Power supply equipment |date=1997 |language=ja |doi=10.11484/jaeri-research-97-010 |last1=青柳 |first1=哲雄 |publisher=日本原子力研究開発機構 }}</ref>

Designs and intentions for the modification varied over the next decade, until February 2007, when the Broader Approach Agreement was signed between Japan and the [[Euratom|European Atomic Energy Community]].<ref>{{Cite book |last=European Commission. Directorate General for Energy. |url=https://data.europa.eu/doi/10.2833/62030 |title=Broader approach :cutting edge fusion energy research activities. |date=2020 |publisher=Publications Office |location=LU |doi=10.2833/62030 |isbn=978-92-76-16659-7 |access-date=2024-02-05 |archive-date=2024-02-25 |archive-url=https://web.archive.org/web/20240225031623/https://op.europa.eu/en/publication-detail/-/publication/d06827b1-59de-11ea-8b81-01aa75ed71a1/language-en |url-status=live }}</ref> In it, the Satellite Tokamak Program established a clear, defined goal for JT-60SA: act as a small-scale ITER. This way, JT-60SA could give hindsight to engineers assembling and operating the full-scale reactor in the future.

It was planned for JT-60 to be disassembled and then upgraded to JT-60SA by adding niobium-titanium superconducting coils by 2010.<ref name="jt60site" /><ref name="JAR2007">{{cite web |url=http://www-jt60.naka.jaea.go.jp/english/annual/07/html/I.JT-60.html |title=JAEA 2006-2007 annual report |quote="3.1.3 Machine Parameters : A bird's eye view of JT-60SA is shown in Fig. I.3.1-1. Typical parameters of JT-60SA are shown in Table I.3.1-1. The maximum plasma current is 5.5 MA with a relatively low aspect ratio plasma (Rp=3.06 m, A=2.65, κ95=1.76, δ95=0.45) and 3.5 MA for an ITER-shaped plasma (Rp=3.15 m, A=3.1, κ95=1.69, δ95=0.36). Inductive operation with 100s flat top duration will be possible within the total available flux swing of 40 Wb. The heating and current drive system will provide 34 MW of neutral beam injection and 7 MW of ECRF. The divertor target is designed to be water-cooled in order to handle heat fluxes up to15 MW/m2 for long time durations. An annual neutron budget of 4x1021 neutrons is foreseen" |access-date=2016-02-16 |archive-url=https://web.archive.org/web/20130106154327/http://www-jt60.naka.jaea.go.jp/english/annual/07/html/I.JT-60.html#I_3.3 |archive-date=2013-01-06 |url-status=dead }} lots of detail on JT-60SA in section 3</ref> 
It was intended for the JT60SA to be able to run with the same shape plasma as ITER.<ref name="JAR2007" />{{rp|3.1.3}} The central solenoid was designed to use niobium-tin (because of the higher (9 T) field).<ref name="JAR2007" />{{rp|3.3.1}} <!-- todo: remove/recycle this paragraph -->

===Assembly===
Construction of the tokamak officially began on {{Date|28.1.2013}} with the assembly of the cryostat base, which was shipped from [[Avilés|Avilés, Spain]] over a 75-day-long journey.{{efn|The ship IYO ({{IMO Number|9300879}}) routed through the [[Panama Canal]]}} The event was highly publicized through local and national news, and reporters from 10 media organizations were able to witness it in person.<ref>{{Cite web |last=martial |date=2013-04-05 |title=JT-60SA: The Tokamak assembly begins |url=https://fusionforenergy.europa.eu/news/jt-60sa-the-tokamak-assembly-begins/ |access-date=2024-03-06 |website=Fusion for Energy |language=en-US |archive-date=2024-02-19 |archive-url=https://web.archive.org/web/20240219165953/https://fusionforenergy.europa.eu/news/jt-60sa-the-tokamak-assembly-begins/ |url-status=live }}</ref><!-- TODO: find what media organizations reported on it and include some notable ones here --><!-- TODO: maybe include info about the 2011 tohoku earthquake? -->

Assembly of the vacuum vessel began in May 2014. The vacuum vessel was manufactured as ten sectors with varying [[Curve#Differentiable arc|arcs]] (20°×1, 30°×2, 40°×7) that had to be installed sequentially. On June 4, 2014, two of ten sectors were installed. In November 2014 seven sectors had been installed. In January 2015 nine sectors had been installed. <!-- yes, this sucks, it's a draft. i dont have the time right now to refine it, im sorry -->

Construction was to continue until 2020 with first plasma planned in September 2020.<ref>{{cite web |title=The JT-60SA project Introduction |url=http://www.jt60sa.org/b/index_nav_1.htm?n1/introduction.htm |url-status=dead |archive-url=https://web.archive.org/web/20160305025820/http://www.jt60sa.org/b/index_nav_1.htm?n1%2Fintroduction.htm |archive-date=5 March 2016 |access-date=6 March 2018 |publisher=[[Japan Atomic Energy Agency]]}}</ref> Assembly was completed on March 30, 2020,<ref>{{cite web |date=April 2020 |title=JT-60SA: World's largest superconducting tokamak completed! |url=http://www.jt60sa.org/b/index_news113.htm?news113/news113.php |series=Newsletter 113 |publisher=National Institutes for Quantum and Radiological Science and Technology |access-date=2020-06-21 |archive-date=2020-06-22 |archive-url=https://web.archive.org/web/20200622003231/http://www.jt60sa.org/b/index_news113.htm?news113/news113.php |url-status=dead }}</ref> and in March 2021 it reached its full design toroidal field successfully, with a current of 25.7&nbsp;kA.<ref>{{Cite web |title=02.03.2021 – JT-60SA successfully reaches its full design toroidal field – JT-60SA |url=https://www.jt60sa.org/wp/02-03-2021-jt-60sa-successfully-reaches-its-full-design-toroidal-field/ |url-status=dead |archive-url=https://web.archive.org/web/20210302144918/https://www.jt60sa.org/wp/02-03-2021-jt-60sa-successfully-reaches-its-full-design-toroidal-field/ |archive-date=2021-03-02 |access-date=2021-03-19 |language=en-GB}}</ref> <!-- this paragraph is temporary, but dont remove it until this section is done -->

===Short circuit===
{{More citations needed section|date=February 2024}}
On March 9, 2021, a coil energization test was being performed on equilibrium [[field coil]] no. 1 (EF1) when the coil current rapidly increased, then suddenly [[flatline]]d. The reactor was safely shut down over the next few minutes, during which the pressure in the cryostat increased from {{val|10e-3|ul=Pa}} to {{val|7000|u=Pa}}. Investigations immediately followed.

The incident, which came to be known as the "EF1 feeder incident", was found to be caused by a major short circuit resulting from insufficient insulation of the [[quench detection]] wire conductor exit. The formed [[Electric arc|arc]] damaged the shells of EF1, causing a helium leak to the cryostat.

In total, 90 locations required repairs and machine sensors needed to be rewired. However, the intricate JT-60SA was designed and assembled with intense precision, meaning access to the machine was sometimes limited. Risks of further delay to plasma operations compounded the issue.<ref>{{Cite web |date=28 November 2022 |title=Team spirit, resilience, and adaptability key to JT-60SA repairs |url=https://fusionforenergy.europa.eu/news/team-spirit-resilience-and-adaptability-key-to-jt-60sa-repairs/ |access-date=7 February 2024 |website=Fusion for Energy |archive-date=2 December 2023 |archive-url=https://web.archive.org/web/20231202153350/https://fusionforenergy.europa.eu/news/team-spirit-resilience-and-adaptability-key-to-jt-60sa-repairs/ |url-status=live }}</ref>

The JT-60SA team was disappointed with the incident, given how close the machine was to operation, but persevered.<!-- explain mental impact of incident and aftermath further -->

Repairs were completed in May 2023 and preparations for operation began.<ref>{{cite web |date=5 June 2023 |title=Operations restart with vacuum pumping on 30.05.2023 |url=https://www.jt60sa.org/wp/operations-restart-with-vacuum-pumping-on-30-05-2023/ |access-date=15 November 2023 |website=JT-60SA |archive-date=15 November 2023 |archive-url=https://web.archive.org/web/20231115015430/https://www.jt60sa.org/wp/operations-restart-with-vacuum-pumping-on-30-05-2023/ |url-status=live }}</ref>

===Present operations===
JT-60SA achieved first plasma on October 23, 2023, making it the largest operational superconducting tokamak in the world as of 2024.<ref name="first"/> The reactor was declared active on December 1, 2023.<ref>{{Cite web |title=EU and Japan celebrate start of operations of the JT-60SA fusion reactor and reaffirm close cooperation on fusion energy - European Commission |url=https://energy.ec.europa.eu/news/eu-and-japan-celebrate-start-operations-jt-60sa-fusion-reactor-and-reaffirm-close-cooperation-fusion-2023-12-01_en |access-date=2024-02-29 |website=energy.ec.europa.eu |language=en |archive-date=2023-12-13 |archive-url=https://web.archive.org/web/20231213113934/https://energy.ec.europa.eu/news/eu-and-japan-celebrate-start-operations-jt-60sa-fusion-reactor-and-reaffirm-close-cooperation-fusion-2023-12-01_en |url-status=live }}</ref>

==Specifications==
<!-- www-pub.iaea.org/mtcd/meetings/PDFplus/2010/cn180/cn180_papers/ov_p-4.pdf --><!-- TODO: get CONCLUSIVE specifications - even papers from JAEA themselves cant agree on the specifications of any of these reactors :sob: -->''(60 stands for JT-60, 60U stands for JT-60U, 60SA stands for JT-60SA) ("60SA I" refers to the initial/integrated research phase of JT-60SA, "60SA II" refers to the extended research phase)''
{| class="wikitable"
|+ style="text-align:left" | Plasma<ref>{{Cite journal |last1=Hosogane |first1=N. |last2=Ninomiya |first2=H. |last3=Matsukawa |first3=M. |last4=Ando |first4=T. |last5=Neyatani |first5=Y. |last6=Horiike |first6=H. |last7=Sakurai |first7=S. |last8=Masaki |first8=K. |last9=Yamamoto |first9=M. |last10=Kodama |first10=K. |last11=Sasajima |first11=T. |last12=Terakado |first12=T. |last13=Ohmori |first13=S. |last14=Ohmori |first14=Y. |last15=Okano |first15=J. |date=November 2002 |title=Development and Operational Experiences of the JT-60U Tokamak and Power Supplies |url=https://www.tandfonline.com/doi/full/10.13182/FST02-A234 |journal=Fusion Science and Technology |language=en |volume=42 |issue=2–3 |pages=368–385 |doi=10.13182/FST02-A234 |bibcode=2002FuST...42..368H |s2cid=120683442 |issn=1536-1055 |access-date=2024-02-25 |archive-date=2024-02-25 |archive-url=https://web.archive.org/web/20240225031557/https://www.tandfonline.com/doi/abs/10.13182/FST02-A234 |url-status=live |url-access=subscription }}</ref><ref name=":2">{{Cite report|title=Annual Report of Division of Thermonuclear Fusion Research and Division of Large Tokamak Development for the Period of April 1, 1976 to March 31, 1977 |date=1978 |language=ja |doi=10.11484/jaeri-m-7479 |author1=核融合研究部 |publisher=日本原子力研究開発機構 }}</ref><ref>{{Cite web |title=Annual report of Fusion Research and Development Directorate of JAEA for FY2008 and FY2009 |date=2011 |url=https://doi.org/10.11484/jaea-review-2011-009 |language=ja |doi=10.11484/jaea-review-2011-009 |author1=核融合研究開発部門 |publisher=日本原子力研究開発機構 }}</ref>
|-
! scope="col" | !! scope="col" | Volume !! scope="col" | Current !! scope="col" | Major radius !! scope="col" | Minor radius 
!Aspect ratio
!Height!! scope="col" | Pulse length
!Elongation
!Triangularity
|-
!60
|
|''{{Val|2.1|u=MA}} - {{Val|2.6|u=MA}}''
|{{Val|3|u=m}}
|''{{Val|0.85|u=m}} - {{Val|0.95|u=m}}''
|''3.52 - 3.15''
|
|{{Val|5|u=s}}
|
|
|-
! scope="row" | 60U
| {{Val|90|u=m3}}|| {{Val|3|u=MA}}|| {{Val|3.4|u=m}}|| {{Val|1|u=m}}
|3.4
| ''{{val|1.5|0.3|u=m}}''|| {{Val|65|u=s}}
|''{{val|1.5|0.3}}''
|
|-
!60SA I
|
|{{Val|5.5|u=MA}}
|{{Val|2.97|u=m}}
|{{Val|1.17|u=m}}
|2.54
|{{Val|2.14|u=m}}
|{{Val|100|u=s}}
|1.83
|0.50
|-
!60SA II
|
|{{Val|5.5|u=MA}}
|{{Val|2.97|u=m}}
|{{Val|1.18|u=m}}
|2.52
|{{Val|2.28|u=m}}
|{{Val|100|u=s}}
|1.93
|0.57
|}
{| class=wikitable
|+ style="text-align:left" | Vacuum Vessel<ref name=":1">{{Cite journal |last1=Ishida |first1=S. |last2=Barabaschi |first2=P. |last3=Kamada |first3=Y. |date=2011-09-01 |title=Overview of the JT-60SA project |url=https://iopscience.iop.org/article/10.1088/0029-5515/51/9/094018 |journal=Nuclear Fusion |volume=51 |issue=9 |pages=094018 |bibcode=2011NucFu..51i4018I |doi=10.1088/0029-5515/51/9/094018 |issn=0029-5515 |s2cid=122120186|url-access=subscription }}</ref><ref name=":2" />
|-
! scope=col | !! scope="col" | Material !! scope="col" | Baking temp. !! scope="col" | One-turn resistance
|-
!60
|[[Inconel 625]]
|{{Val|500|u=degC}}
|> {{Val|1.3|u=mΩ}}
|-
! scope="row" | 60U
| Inconel 625|| {{Val|300|u=degC}}|| {{Val|0.2|u=mΩ}}
|-
! scope=row | 60SA
| [[Stainless steel|SS 316L]]|| {{Val|200|u=degC}}|| {{Val|16|u=µΩ}}
|}
{| class=wikitable
|+ style="text-align:left" | Toroidal Field Coils<ref name=":2" />
|-
! scope=col | !! scope="col" | # 
!Turns!! scope="col" | Material !! scope="col" | Coil current
!Inductance
!Resistance
![[Time constant]]
|-
!60
|18
|1296
|
|52.1 kA
|2.1 H
|84 mΩ
|25 s
|-
! scope="row" | 60U
| 18
|1296|| AgOFCu|| 52.1 kA
|2.1 H
|97 mΩ
|21.65 s
|-
! scope=row | 60SA
|
| || ||
|
|
|
|}

==Notes==
{{Notelist}}

==References==
{{Reflist}}

==External links==
* {{Official website|https://www.jt60sa.org/wp/}} of JT-60SA ([https://www.qst.go.jp/site/jt60-english/ JT-60/JT-60U])
* {{Official website|https://www.qst.go.jp/site/qst-english/}} of QST
* {{Official website|https://www.jaea.go.jp/english/}} of JAEA ([https://web.archive.org/web/20070908014439/http://www.jaea.go.jp/jaeri/english/index.html JAERI])
* [https://jopss.jaea.go.jp/search/servlet/interSearch?language=1 JAEA Originated Papers Searching System]
* {{Official website|https://fusionforenergy.europa.eu/}} of Fusion for Energy
<!-- * [http://www.yomiuri.co.jp/dy/features/science/20060511TDY04004.htm JT-60's Newly Achieved Plasma Record (Japanese) ] {{Webarchive|url=https://web.archive.org/web/20060603155534/http://www.yomiuri.co.jp/dy/features/science/20060511TDY04004.htm |date=2006-06-03 }}
* [https://web.archive.org/web/20130106002319/http://www-jt60.naka.jaea.go.jp/english/html/exp_rep/rep36.html World Highest Fusion Triple Product Marked in High-βp H-mode Plasmas - Aug 1996] 1.5*10<sup>21</sup> m<sup>−3</sup> s keV -->
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[[Category:Tokamaks]]
[[Category:Nuclear technology in Japan]]