Fusion reactions are inhibited by the electrical repulsive force that acts between two positively charged nuclei. For fusion to occur, the two nuclei must approach each other at high speed to overcome the electrical repulsion and attain a sufficiently small separation (less than one-trillionth of a centimeter) that the short-range strong nuclear force dominates. For the production of useful amounts of energy, a large number of nuclei must under go fusion: that is to say, a gas of fusing nuclei must be produced. In a gas at extremely high temperature, the average nucleus contains sufficient kinetic energy to undergo fusion. Such a medium can be produced by heating an ordinary