Tokamak
A tokamak (; ) 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 developed to produce controlled thermonuclear fusion power. , it is the leading candidate for a practical fusion reactor.

Tokamaks were initially conceptualized in the 1950s by Soviet physicists Igor Tamm and Andrei Sakharov, inspired by a letter by Oleg Lavrentiev. The first working tokamak was attributed to the work of Natan Yavlinsky on the T-1 in 1958. It had been demonstrated that a stable plasma equilibrium requires magnetic field lines that wind around the torus in a helix. Devices like the z-pinch and stellarator had attempted this, but demonstrated serious instabilities. It was the development of the concept now known as the safety factor (labelled "q" in mathematical notation) that guided tokamak development; by arranging the reactor so this critical factor "q" was always greater than 1, the tokamaks strongly suppressed the instabilities which plagued earlier designs.

By the mid-1960s, the tokamak designs began to show greatly improved performance. The initial results were released in 1965, but were ignored; Lyman Spitzer dismissed them out of hand after noting potential problems in their system for measuring temperatures. A second set of results was published in 1968, this time claiming performance far in advance of any other machine. When these were also met skeptically, the Soviets invited a delegation from the United Kingdom to make their own measurements. These confirmed the Soviet results, and their 1969 publication resulted in a stampede of tokamak construction.

By the mid-1970s, dozens of tokamaks were in use around the world. By the late 1970s, these machines had reached all of the conditions needed for practical fusion, although not at the same time nor in a single reactor. With the goal of breakeven (a fusion energy gain factor equal to 1) now in sight, a new series of machines were designed that would run on a fusion fuel of deuterium and tritium. These machines, notably the Joint European Torus (JET), Tokamak Fusion Test Reactor (TFTR), had the explicit goal of reaching breakeven.

Instead, these machines demonstrated new problems that limited their performance. Solving these would require a much larger and more expensive machine, beyond the abilities of any one country. After an initial agreement between Ronald Reagan and Mikhail Gorbachev in November 1985, the International Thermonuclear Experimental Reactor (ITER) effort emerged and remains the primary international effort to develop practical fusion power. Many smaller designs, and offshoots like the spherical tokamak, continue to be used to investigate performance parameters and other issues. , JET remains the record holder for fusion output, reaching 16 MW of output for 24 MW of input heating power.
Q11408
magnetic field
Concept
Q10251
plasma
Concept
Q12510
torus
Concept
Q939954
magnetic confinement
Concept
Q7783221
thermonuclear
UNK
Q641442
fusion power
Concept
Q641442
fusion reactor
Concept
Q155759
Igor Tamm
PER
Q997
Andrei Sakharov
PER
Q4252113
Oleg Lavrentiev
PER
Q19909936
Natan Yavlinsky
PER
Q4379538
stable plasma equilibrium
UNK
Q11408
magnetic field line
Concept
Q201717
helix
Concept
Q3141097
z-pinch
MISC
Q1360597
stellarator
Concept
Q7398642
safety factor
UNK
Q431503
Lyman Spitzer
PER
Q145
United Kingdom
LOC
Q5510279
fusion energy gain factor
UNK
Q102296
deuterium
Concept
Q54389
tritium
Concept
Q1702534
Joint European Torus
MISC
Q3277174
Tokamak Fusion Test Reactor
MISC
Q9960
Ronald Reagan
PER
Q30487
Mikhail Gorbachev
PER
Q191788
International Thermonuclear Experimental Reactor
ORG
Q7576717
spherical tokamak
Concept
Q188589
Tokamak
Concept
1950-01-01T00:00:00Z^^http://www.w3.org/2001/XMLSchema#dateTime
1950
DATE
1958-01-01T00:00:00Z^^http://www.w3.org/2001/XMLSchema#dateTime
1958
DATE
1965-01-01T00:00:00Z^^http://www.w3.org/2001/XMLSchema#dateTime
1965
DATE
1968-01-01T00:00:00Z^^http://www.w3.org/2001/XMLSchema#dateTime
1968
DATE
1969-01-01T00:00:00Z^^http://www.w3.org/2001/XMLSchema#dateTime
1969
DATE
1970-01-01T00:00:00Z^^http://www.w3.org/2001/XMLSchema#dateTime
1970
DATE
1985-11-01T00:00:00Z^^http://www.w3.org/2001/XMLSchema#dateTime
November 1985
DATE
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-1
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1
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-1960
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-1970
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16
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24
NUMBER
used by
discoverer or inventor
discoverer or inventor
instance of