Nuclear fusion: the energy that powers our solar system. This is the reaction that takes place in our sun. Hydrogen converts to helium, and in the process, gives of inordinate amounts of energy.
Nuclear fusion is basically the opposite reaction of fission. Instead of splitting nuclei apart, producing energy, fusion combines relatively light nuclei, forming a heavier nucleus and releasing far more energy. An example of this can be found in the sun, as mentioned before, with the fusion of hydrogen nuclei to form helium nuclei.
with 2.5 x 109 kJ/mol of energy produced.
There are several forms of fusion, including simple proton-proton reactions used in nuclear fusion, carbon-nitrogen cycles used in the largest and most intense stellar fusion, fusion of helium and heavier elements in older stars, and deuterium-tritium fusion in our reactor and hydrogen bomb designs. In most fusion reactions, the mass of the products is about .6-.7 percent less than the mass of the reactants; as in fission, the extra mass is converted into energy. Fusion releases much greater amounts of energy than fission, as well as producing less radiation and relatively benevolent products. This makes nuclear fusion attractive as an energy source. Deuterium can be extracted from seawater, tritium is easily formed from the common metal lithium, and the only product of the process (other than tremendous amounts of energy) is helium gas. Only parts of the reactor itself would become radioactive, and the contamination would be much less than that found in today's fission reactors. Finally, fusion is much safer: if a containment system failed, the reaction would simply stop and nearly-harmless hydrogen and helium gas would be released.
One of the difficulties that scientists have faced in their quest to bring the power of nuclear fusion to the world is that the reaction above requires temperatures in the range of 106 to 107 Kelvin to bring the charged nuclei together. Since both nuclei are positively charged, a formidable amount of kinetic force is required to overcome nuclear repulsion. At the high temperatures required to produce such a reaction, atoms do not exist. Instead, there exists a state of plasma, free-floating atoms with their electrons ripped off due to the incredible nature of their surroundings. . . literally like the center of the sun. To achieve the high temperatures required for fusion in the form of a hydrogen bomb, a fission bomb (atom bomb) must first be set off, setting the stage for the fusion reaction.
Since the particles in a plasma are electrically charged, magnetic fields can be used to contain the gas. Radio waves, particle beams, and magnetic compression are some strategies being investigated to heat the plasma mixture to the proper temperatures. Recently, an experimental reactor sustained fusion for a total of four seconds. While the amount of energy extracted was much lower than input, scientists are making progress. Needless to say, common household usage of fusion is not quite feasible yet. But we're getting there.