JT-60 (short for Japan Torus-60) is a large research
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 ...
, the flagship of
Japan
Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...
's
magnetic fusion program, previously run by the
Japan Atomic Energy Research Institute
The Japan Atomic Energy Research Institute ( ja, 日本原子力研究所) (JAERI) is a former semi-governmental organization that existed for the purpose of further nuclear power in Japan. It was created in June 1956 by the Atomic Energy Basic La ...
(JAERI) and currently run by the
Japan Atomic Energy Agency
The is an Independent Administrative Institution formed on October 1, 2005 by a merger of two previous semi-governmental organizations. While it inherited the activities of both JNC and JAERI, it also inherited the nickname of JAERI, "Genken" ...
's (JAEA) Naka Fusion Institute in
Ibaraki Prefecture
is a Prefectures of Japan, prefecture of Japan located in the Kantō region of Honshu. Ibaraki Prefecture has a population of 2,871,199 (1 June 2019) and has a geographic area of . Ibaraki Prefecture borders Fukushima Prefecture to the north, ...
. It is properly an
advanced 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 ...
, including a D-shaped plasma cross-section and active feedback control.
First designed in the 1970s as the "Breakeven Plasma Test Facility" (BPTF), the goal of the system was to reach
breakeven fusion power, a goal set for the US's
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 wh ...
, 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. , JT-60 currently holds the record for the highest value of the
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 ...
achieved: = .
[JT-60 Operational History and the Progress of Plasma Performance]
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.
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)
During
deuterium
Deuterium (or hydrogen-2, symbol or deuterium, also known as heavy hydrogen) is one of two Stable isotope ratio, stable isotopes of hydrogen (the other being Hydrogen atom, protium, or hydrogen-1). The atomic nucleus, nucleus of a deuterium ato ...
(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
Deuterium (or hydrogen-2, symbol or deuterium, also known as heavy hydrogen) is one of two Stable isotope ratio, stable isotopes of hydrogen (the other being Hydrogen atom, protium, or hydrogen-1). The atomic nucleus, nucleus of a deuterium ato ...
and
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 ...
(D–T fuel).
JT-60 does not have the facilities to handle tritium; only the
JET tokamak in the
United Kingdom
The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and North ...
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
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 bein ...
(the ratio of fusion power to input power) ''Q'' = 1.25.
A self-sustaining nuclear fusion reaction would need a value of ''Q'' that is greater than 5.
[
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.]
On May 9, 2006, the JAEA announced that the JT-60 had achieved a 28.6 second plasma duration time.[
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
Beta (, ; uppercase , lowercase , or cursive ; grc, βῆτα, bē̂ta or ell, βήτα, víta) is the second letter of the Greek alphabet. In the system of Greek numerals, it has a value of 2. In Modern Greek, it represents the voiced labiod ...
steady-state operation in the use of reduced radio-activation ferritic
A ferrite is a ceramic material made by mixing and firing large proportions of iron(III) oxide (Fe2O3, rust) blended with small proportions of one or more additional metallic elements, such as strontium, barium, manganese, nickel, and zinc. Th ...
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
Superconductivity is a set of physical properties observed in certain materials where Electrical resistance and conductance, electrical resistance vanishes and magnetic field, magnetic flux fields are expelled from the material. Any material e ...
coils by 2010.[ lots of detail on JT-60SA in section 3]
It was intended for the JT60SA to be able to run with the same shape plasma as 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 Earth ...
.[ The central solenoid was designed to use niobium-tin (because of the higher (9 T) field).][
Construction of the tokamak officially began in 2013, and it was to continue until 2020 with first plasma planned in September 2020. Assembly was completed in the spring of 2020, and in March 2021 it reached its full design toroidal field successfully, with a current of 25.7kA.] A test of the poloidal field coils in March 2021 suffered a short circuit leading to a lengthy investigation and repair.[''Team spirit, resilience, and adaptability key to JT-60SA repairs'' 28 Nov 2022]
/ref>
References
External links
* of the JT-60
* of the JT-60SA
1.5*1021 m−3 s keV
{{fusion experiments
Tokamaks
Nuclear technology in Japan