/toh"keuh mak', tok"euh-/ , n. Physics.
a type of experimental nuclear fusion reactor in which a plasma of atoms circulates in a toroidal tube and is confined to a narrow beam by an electromagnetic field.
[ 1960-65; tokamák, acronym from toroidál'naya kámera s aksiál'nym magnítnym pólem toroidal chamber with an axial magnetic field ]