Electron cyclotron resonance heating

A tokamak (Russian: токама́к) is a device that uses a powerful magnetic field to confine plasma in the shape of a torus. The tokamak is one of the several types of magnetic confinement devices being developed to contain the hot plasma needed for producing controlled thermonuclear fusion power. As of 2017^[update], it is the leading candidate for a practical fusion reactor.

Tokamaks were invented in the 1950s by Soviet physicists Igor Tamm and Andrei Sakharov, inspired by an original idea of Oleg Lavrentiev. It had earlier been demonstrated that a stable plasma equilibrium requires magnetic field lines that move around the torus in a helical shape. Earlier devices like the z-pinch and stellarator had attempted this, but demonstrated serious instabilities anyway. It was the development of the concept now known as the safety factor that guided tokamak development; by arranging the reactor so the critical factor q was always greater than 1, the tokamaks strongly suppressed the kink instability that plagued earlier designs.

The first tokamak, T-1, began operation in 1958. By the mid-1960s their performance had improved so much that an initial release of results in 1965 was largely ignored. Lyman Spitzer, inventor of the stellarator, dismissed them out of hand. A second set of results was published in 1968, this time claiming performance far in advance of any other machine. Recognizing these claims might be dismissed as well, the Soviet delegation invited a team from the United Kingdom to verify the result. Their 1969 publication confirmed the dramatic improvements, resulting in a stampede of tokamak construction around the world. The performance was such an advance that the US abandoned the stellarator approach and converted their latest machine to a tokamak.

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