Tokamaks

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 several types of magnetic confinement devices being developed to contain the hot plasma needed for producing controlled thermonuclear fusion power. It is the leading candidate for a practical fusion reactor. Magnetic fields are used for confinement since no solid material could withstand the extremely high temperature of the plasma. The world's largest tokamak project is the ITER (International Thermonuclear Experimental Reactor) being constructed in Saint-Paul-lès-Durance, in southern France. Scheduled to begin operation in 2020, it is expected to produce an output power of 500 megawatts.

Tokamaks were invented in the 1950s by Soviet physicists Igor Tamm and Andrei Sakharov, inspired by an original idea of Oleg Lavrentiev. Achieving a stable plasma equilibrium requires magnetic field lines that move around the torus in a helical shape. Such a helical field can be generated by adding a toroidal field (traveling around the torus in circles) and a poloidal field (traveling in circles orthogonal to the toroidal field). In a tokamak, the toroidal field is produced by electromagnets surrounding the torus; the poloidal field is the result of a toroidal electric current that flows inside the plasma. This current is induced inside the plasma with a second set of electromagnets.

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