Fusion reaction is a nuclear 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. There is a small mass difference, say m, between the initial and the final reaction products which gets converted into energy through Einstein’s equation E=mc2, c being the speed of light. This energy comes out in the form of kinetic energy of the product particles and can be converted into electricity by conventional technologies.
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.
A Deuterium and a Tritium nucleus fuse to produce a Helium nucleus and a neutron. The reaction produces 17.6 MeV of energy, out of which the Helium carries 3.5 MeV and the neutron 14.1 MeV. In a plasma undergoing fusion, the reactions can be self sustained, as part of the kinetic energy of the resulting charged Helium can be used to maintain the very high temperatures required to sustain the fusion reactions.