The word tokamak is a transliteration of the Russian word токамак, a possible of this language acronym of: toroidál'naya kámera s magnítnymi katúshkami or toroidal chamber with magnetic coils. It describes a machine which uses a powerful magnetic field generated by external magnets to confine plasma in the shape of an axially symmetrical torus. The tokamak is the leading candidate of magnetic confinement fusion designs being developed to produce controlled thermonuclear fusion power.

In 1950, Soviet Army sergeant Oleg Lavrentiev proposed a groundbreaking method for achieving controlled nuclear fusion using electrostatic fields to contain hot plasma. His proposal was swiftly reviewed by physicist Andrei Sakharov, who, despite concerns regarding plasma interacting with electrode wires, recognized the concept's potential and collaborated with Igor Tamm to develop a detailed reactor study.

The high priority placed on Lavrentiev's idea was evidenced by the remarkably rapid transition from his initial letter in July to a formal funding request for a fusion reactor by January 1951 to adjusting the original concept and building the tokamak reactor. There are other fusion concepts of course, but the argument was that if the tokamak torus geometry was improved further then it could provide the topology similar to that of the spherical sun where fusion is the source of energy, so is it?

Poincaré conjecture - every three-dimensional topological manifold which is closed, connected, and has trivial fundamental group is homeomorphic to the three-dimensional sphere.

As per Poincaré conjecture, and from a pure geometrical point of view, a torus cannot close to a sphere. True, researchers did set out to change aspects ratios of different tokamak configurations (e.g. spheromaks), but this came at the expense of the central solenoid unit where heating and confining currents are originating. However, the tokamak remains a versatile machine to study a variety of science and technology topics.

Image: Neither of the two-colored loops on this torus can be continuously tightened to a point. A torus is not homeomorphic to a sphere.