Physics:JT-60

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Short description: Japanese tokamak
JT-60
Japan Torus-60
Device TypeTokamak
LocationNaka, Ibaraki Prefecture, Japan
AffiliationJapan Atomic Energy Agency
Technical specifications
Major Radius3.4 m (11 ft)
Minor Radius1.0 m (3 ft 3 in)
Plasma volume90 m3
Magnetic field4 T (40,000 G) (toroidal)
Discharge duration65 s
History
Year(s) of operation1985 – 2010
Preceded byJFT-2M
Succeeded byJT-60SA
Related devicesTFTR

JT-60 (short for Japan Torus-60) is a large research tokamak, the flagship of Japan 's magnetic fusion program, previously run by the Japan Atomic Energy Research Institute (JAERI) and later by the Japan Atomic Energy Agency's (JAEA) Naka Fusion Institute in Naka, Ibaraki Prefecture.[1] As of 2023 the device is known as JT-60SA and it is the largest operational superconducting tokamak in the world to date,[2] and was built and is operated jointly by the European Union and Japan.[3] SA stands for super advanced tokamak, including a D-shaped plasma cross-section, superconducting coils, and active feedback control.

Original design

JT-60 was first designed in the 1970's as the "Breakeven Plasma Test Facility" (BPTF),[4] a scaled-up version of the JFT-2M[5] aimed at achieving breakeven fusion power. It began operations in 1985, and much like the United States 's TFTR and the United Kingdom 's JET that began operations only shortly before it with similar goals, JT-60 demonstrated performance far below predictions.

Over the next two decades, JET and JT-60 led the effort to regain the performance originally expected of these machines. JT-60 underwent two major modifications during this time, producing JT-60A[when?], and then JT-60U (for "upgrade") in 1991.[6] These changes resulted in significant improvements in plasma performance. (As of 2018), JT-60 currently holds the record for the highest value of the fusion triple product achieved: 1.77×1028 K·s·m−3 = 1.53×1021 keV·s·m−3.[7][8] To date, JT-60 has the world record for the hottest ion temperature ever achieved (522 million °C); this record defeated the TFTR machine at Princeton in 1996.[9]

In 2020, JT60 was upgraded to JT-60SA. In 2021 and 2022, a poloidal field coil short circuit was investigated, and repairs were done.

JT-60U (Upgrade)

On October 31, 1996, JT-60U successfully achieved extrapolated breakeven with a factor of QDTeq = 1.05 at 2.8 MA. Put simply, if the homogenous deuterium fuel was theoretically replaced with a 1:1 mix of deuterium and tritium, the fusion reaction would have created an energy output 1.05 times the energy used to start the reaction. JT-60U was not equipped to utilize tritium, as it would add extensive costs and safety risks.

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.[10][11][12] 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 extrapolated fusion energy gain factor of QDTeq = 1.25 at 2.6 MA.[13][14][15]

In December 1998, a modification to the vacuum pumping system that began in 1994 was completed. In particular, twelve turbomolecular pumps with oil bearings and four oil sealed rotary vacuum pumps were replaced with magnetically suspended turbomolecular pumps and dry vacuum pumps. The modification reduced the 15-year-old system's consumption of liquid nitrogen by two thirds.[16]

In fiscal year 2003, the plasma discharge duration of JT-60U was successfully extended from 15 s to 65 s.[17]

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.[18][19] 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 molecular beam injection (SMBI) system was installed in JT-60U. The system's design was a collaboration between Cadarache, CEA, and JAEA.[20]

JT-60SA

It was planned for JT-60 to be disassembled and then upgraded to JT-60SA by adding niobium-titanium superconducting coils by 2010.[7][21] It was intended for the JT60SA to be able to run with the same shape plasma as ITER.[21]:3.1.3 The central solenoid was designed to use niobium-tin (because of the higher (9 T) field).[21]:3.3.1

Construction of the tokamak officially began in January 2013,[22] and it was to continue until 2020 with first plasma planned in September 2020.[23] Assembly was completed in the spring of 2020,[24] and in March 2021 it reached its full design toroidal field successfully, with a current of 25.7kA.[25] A test of the poloidal field coils in March 2021 suffered a short circuit leading to a lengthy investigation and repair.[26]

Repairs were completed in May 2023 and preparations for operation began.[27] First plasma was achieved on 23 October 2023 making JT-60SA the largest operational superconducting tokamak in the world to date.[2] The reactor was declared active on 1 December 2023. [28]

References

  1. ↑ "Archived copy". http://www.naka.jaea.go.jp/english/NAKA-HPe.html. 
  2. ↑ 2.0 2.1 "First plasma 23 October". 24 October 2023. https://www.jt60sa.org/wp/first-plasma-23-october/. 
  3. ↑ "What is JT-60SA?". https://www.jt60sa.org/wp/. 
  4. ↑ Arnoux, Robert (31 May 2011). "Taking the Big Leap". ITER Newsline. https://www.iter.org/newsline/179/731. 
  5. ↑ "JFT-2M Project | Introduction of JFT-2M - National Institutes for Quantum Science and Technology". https://www.qst.go.jp/site/jt60-english/6685.html. 
  6. ↑ Naka Fusion Institute (June 2008). FUSION - Future Energy of the Earth. Japan Atomic Energy Agency. p. 12. https://www.qst.go.jp/uploaded/attachment/5304.pdf. Retrieved 25 January 2024. 
  7. ↑ 7.0 7.1 "JT-60 HOME PAGE". Japan Atomic Energy Agency. https://www-jt60.naka.qst.go.jp/english/jt60/project/html/history.html. 
  8. ↑ JT-60 Operational History and the Progress of Plasma Performance
  9. ↑ "Plasma physics found in JT-60 tokamak over the last 20 years". https://jopss.jaea.go.jp/search/servlet/search?5017810&language=1. 
  10. ↑ Naka-machi; Naka-gun; Ibaraki-ken (1997). Annual Report from April 1, 1996 to March 31, 1997 (Report). Naka Fusion Research Establishment. p. 1. https://www.qst.go.jp/uploaded/attachment/7664.pdf. Retrieved 26 January 2024. "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." 
  11. ↑ Naka-machi; Naka-gun; Ibaraki-ken (1 October 1998). Annual Report of Naka Fusion Research Establishment from April 1, 1997 to March 31, 1998 (Report). Naka Fusion Research Establishment. p. 1. https://www.qst.go.jp/uploaded/attachment/7665.pdf. Retrieved 26 January 2024. "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." 
  12. ↑ Fusion energy 1996. 3. Publication / Division of Scientific and Technical Information, International Atomic Energy Agency. Vienna. 1997. ISBN 978-92-0-103997-2. 
  13. ↑ "JT-60U Reaches 1.25 of Equivalent Fusion Power Gain". 7 August 1998. http://www-jt60.naka.jaea.go.jp/english/html/exp_rep/rep46.html. 
  14. ↑ Clery, Daniel (2014-07-29) (in en). A Piece of the Sun: The Quest for Fusion Energy. Overlook Press. ISBN 978-1-4683-1041-2. https://books.google.com/books?id=EGcjCQAAQBAJ&pg=PT103&lpg=PT103&dq=JT-60U+q=1.2. 
  15. ↑ HIGH PERFORMANCE EXPERIMENTS IN JT-60U REVERSED SHEAR DISCHARGES
  16. ↑ Annual Report of Naka Fusion Research Establishment from April 1, 1998 to March 31, 1999 (Report). https://www.qst.go.jp/uploaded/attachment/7666.pdf. 
  17. ↑ Annual Report of Naka Fusion Research Establishment from April 1, 2003 to March 31, 2004 (Report). https://www.qst.go.jp/uploaded/attachment/7659.pdf. 
  18. ↑ "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 -" (Press release). Japan Atomic Energy Agency. 9 May 2006. Retrieved 5 December 2016.
  19. ↑ ferromagnet diagrams
  20. ↑ Annual Report of Fusion Research and Development Directorate of JAEA from April 1, 2007 to March 31, 2008 (Report). 20 October 1998. p. 18. https://www.qst.go.jp/uploaded/attachment/7663.pdf. Retrieved 30 January 2024. 
  21. ↑ 21.0 21.1 21.2 "JAEA 2006-2007 annual report". http://www-jt60.naka.jaea.go.jp/english/annual/07/html/I.JT-60.html. ""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""  lots of detail on JT-60SA in section 3
  22. ↑ JT-60SA - Toward the Realization of Fusion Energy. January 2021. p. 3. https://www.qst.go.jp/uploaded/attachment/20800.pdf. Retrieved 26 January 2024. 
  23. ↑ "The JT-60SA project Introduction". Japan Atomic Energy Agency. http://www.jt60sa.org/b/index_nav_1.htm?n1/introduction.htm. 
  24. ↑ "JT-60SA: World's largest superconducting tokamak completed!". National Institutes for Quantum and Radiological Science and Technology. April 2020. http://www.jt60sa.org/b/index_news113.htm?news113/news113.php. 
  25. ↑ "02.03.2021 – JT-60SA successfully reaches its full design toroidal field – JT-60SA" (in en-GB). https://www.jt60sa.org/wp/02-03-2021-jt-60sa-successfully-reaches-its-full-design-toroidal-field/. 
  26. ↑ Team spirit, resilience, and adaptability key to JT-60SA repairs 28 Nov 2022
  27. ↑ "Operations restart with vacuum pumping on 30.05.2023". 5 June 2023. https://www.jt60sa.org/wp/operations-restart-with-vacuum-pumping-on-30-05-2023/. 
  28. ↑ EU Press release 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

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