What is Fusion?

Fusion reaction is a process by which nuclei of two light elements fuse to produce a fast, heavier nucleus and an even faster nucleon, i.e. a neutron or a proton. For such a reaction to occur, the reacting nuclei need to have enough kinetic energy to overcome the repulsive electrostatic barrier between any two of them. For this to happen in laboratory experiments, the reacting particles need to be heated to very high temperatures, more than the temperature at the core of the sun. At such high temperatures, matter remains in plasma state, a collection of charged particles. The brightest example of fusion reactions in nature is the Sun and the stars in which hydrogen nuclei, bound together by strong gravitational force, fuse in a chain of reactions to produce finally Helium. The mass of the resulting helium atom is not the exact sum of the initial atoms, however—some mass has been lost and great amounts of energy have been gained. This is what Einstein's famous formula E=mc² describes: the tiny bit of lost mass (m), multiplied by the square of the speed of light (c²), results in a very large figure (E), which is the amount of energy created by a fusion reaction.