Complex sentence: A tokamak is a machine producing a toroidal magnetic field for confining a plasma which is characterized by azimuthal (rotational) symmetry and the use of a plasma-borne electric current to generate the helical component of the magnetic field necessary for stable equilibrium.
Split into simpler sentences: A tokamak is a machine producing a toroidal magnetic field for confining a plasma. The tokamak is characterized by azimuthal (rotational) symmetry and the use of the plasma-borne electric current to generate the helical component of the magnetic field necessary for stable equilibrium.