An efficient thermal fusion reactor of dimensions possible on the earth would have to have a much higher rate for the individual reactions. This means the required temperature in a reactor would have to be higher than the internal temperature of the sun. Another important condition is a highly densed state of plasma to produce a large amount of energy to sustain fusion reactions. About 30 g of D is absorbed in 1000 l of sea water. The 'tokamak' derives its name from the Russian words for toroidal magnetic chamber.
Tokamak is the fusion reactor with doughnut shape.
The main structures of tokamak consist of plasma vacuum chamber, blanket, shield, central solenoid, and toroidal and poloidal field coil. Central solenoid induces an electric field. This field produces plasma in the chamber. This field prevents plasma particles from drifting out of the confinement region of chamber. In the vacuum chamber , fusion reactions take place.