JT-60

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 currently run by the Japan Atomic Energy Agency's (JAEA) Naka Fusion Institute in Ibaraki Prefecture.[1] It is properly an advanced tokamak, including a D-shaped plasma cross-section and active feedback control.

JT-60
Japan Torus-60
Device TypeTokamak
LocationIbaraki 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)
History
Year(s) of operation1985 – 2010
Succeeded byJT-60SA
Related devicesTFTR

First designed in the 1970s as the "Breakeven Plasma Test Facility" (BPTF),[2] the goal of the system was to reach breakeven, a goal also set for the US's TFTR, the UK's JET and the Soviet T-15. JT-60 began operations in 1985, and like the TFTR and JET that began operations only shortly before it, 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, and then JT-60U (for "upgrade"). 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.[3][4]

JT-60U (Upgrade)

During deuterium (D–D fuel) plasma experiments in 1998, plasma conditions were achieved which would have achieved break-even—the point where the power produced by the fusion reactions equals the power supplied to operate the machine—if the D–D fuel were replaced with a 1:1 mix of deuterium and tritium (D–T fuel). JT-60 does not have the facilities to handle tritium; only the JET tokamak in the United Kingdom has such facilities as of 2018. In fusion terminology, JT-60 achieved conditions which in D–T would have provided a fusion energy gain factor (the ratio of fusion power to input power) Q = 1.25.[5][6][7] A self-sustaining nuclear fusion reaction would need a value of Q that is greater than 5.[3][8][9]

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.[10][11] On May 9, 2006, the JAEA announced that the JT-60 had achieved a 28.6 second plasma duration time.[10] The JAEA used new parts in the JT-60, having improved its capability to hold the plasma in its powerful toroidal magnetic field. The main future objective of JT-60 is to realize high-beta steady-state operation in the use of reduced radio-activation ferritic steel in a collision-less regime.

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.[3][12] It is intended to be able to run with the same shape plasma as ITER.[12]:3.1.3 The central solenoid will use niobium-tin (because of the higher (9 T) field).[12]:3.3.1

Construction of the tokamak officially began in 2013, and will continue until 2020 with first plasma planned in September 2020.[13] Assembly was completed in the spring of 2020.[14]

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References
  2. Arnoux, Robert (31 May 2011). "Taking the Big Leap". ITER Newsline.
  3. "JT-60 HOME PAGE". Japan Atomic Energy Agency. Archived from the original on 8 December 2015. Retrieved 5 December 2015.
  4. JT-60 Operational History and the Progress of Plasma Performance Archived 2016-02-23 at the Wayback Machine
  5. "JT-60U Reaches 1.25 of Equivalent Fusion Power Gain". 7 August 1998. Archived from the original on 6 January 2013. Retrieved 5 December 2016.
  6. Daniel Clery. A Piece of the Sun: The Quest for Fusion Energy
  7. HIGH PERFORMANCE EXPERIMENTS IN JT-60U REVERSED SHEAR DISCHARGES
  8. "NSTX Research Program Five Year Plan for 2009-2013" (PDF). National Spherical Torus Experiment website. p. 24. Retrieved 5 December 2015.
  9. Wesson, John (November 1999). "The Science Of JET" (PDF). EUROfusion. Retrieved 5 December 2015.
  10. "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.
  11. ferromagnet diagrams
  12. "JAEA 2006-2007 annual report". Archived from the original on 2013-01-06. Retrieved 2016-02-16. 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
  13. "The JT-60SA project Introduction". Japan Atomic Energy Agency. Retrieved 6 March 2018.
  14. "JT-60SA: World's largest superconducting tokamak completed!". Newsletter 113. National Institutes for Quantum and Radiological Science and Technology. April 2020.
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