Nuclear fusion is the process by which two light atomic nuclei unite into one to form one heavier nucleus with the subsequent release of energy. Nuclear fusion occurs naturally in stars, but artificial fusion has also been achieved, although not yet completely controlled. When light nuclei are forced together, they will fuse with a release of energy because the mass of the combination will be less than the sum of the masses of the individual nuclei. For the artificial nuclear fusion, man has used two heavy hydrogen atoms; deuterium and tritium.
Deuterium-Tritium fusion yields 17.6 MeV of energy but requires a temperature of approximately 40 million Kelvins to overcome the coulomb barrier and ignite it. Thus, it takes considerable energy to force nuclei to fuse, even those of the lightest element, hydrogen. This is because all nuclei have a positive charge due to their protons, and as like charges repel each other, nuclei strongly resist being put too close together. Heated to thermonuclear temperatures, they can overcome this electromagnetic repulsion and get close enough for the attractive nuclear force to be sufficiently strong to achieve fusion.
When the fusion reaction is a sustained uncontrolled chain, it can result in a thermonuclear explosion, such as that generated by a hydrogen bomb, which is triggered not by TNT, but by an atomic bomb! The central core of a hydrogen bomb is a mass made up of trillions of deuterium and tritium (isotopes of hydrogen). These hydrogen atoms have one or two extra neutrons in each nucleus. Small atomic bombs (A) scattered around the outside of the core cause the deuterium and tritium to be squeezed into a very dense mass, which initiates a process called nuclear fusion, releasing great quantities of energy.
Producing fusion power for the production of electricity is not easy as research into controlled fusion has been conducted for 50 years. It has been accompanied by extreme scientific and technological difficulties, and it resulted in steady progress. Controlled fusion reaction have been demonstrated in a few tokamak-type reactors around the world. As a result, a workable design of a reactor was produced. It will deliver ten times more fusion energy than the amount of energy needed to heat up its plasma to required temperatures.