Definition : Fusion is a reaction where two or more nuclei fuse together to form one new nucleus.

This reaction can produce large amounts of energy. Where does the energy come from ? Einstein’s famous equation :

E=mc²

(where E=energy, m=mass and c=speed of light)

gives the answer . If the mass of nuclei after a reaction is less than that before, some mass must have been converted to energy. An atom consists of a tiny nucleus with negatively-charged electrons orbiting in a cloud around it. The nucleus itself is made of particles with a positive electric charge called protons and particles with no electric charge called neutrons. A powerful attraction called the 'strong force' glues the neutrons and protons together.

Some Fuels involved in Fusion :

• Deuterium (found in sea water)

• Lithium (found in the Earth’s crust), used to make tritium inside the reactor.

(Deuterium and tritium are two kinds of hydrogen. They are the fuels most likely to produce a useful fusion reaction.)

Method:

• The fuels are put in a special doughnut-shaped vessel called a Tokamak (cyclotron).

• The superconducting magnets are turned on to keep the plasma circulating without crashing into the walls of the doughnut (to prevent energy losses).

• The fuels are heated to about 100 million degrees celsius.

Neutrons in the plasma escape from the magnetic field to react with the Lithium in the surrounding vessel to produce tritium, which is extracted and recycled back into the reactor. If conditions of very high temperature and a certain pressure (2-3 times that of Earth’s atmospheric pressure) are reached, the nuclei of Deuterium and Tritium will fuse together to form helium and energy will be released as heat. This energy can be used to produce steam and drive turbines connected to generators.

²₁H + ³₁H ⁴₂He + 3.6 MeV + ¹₀n + 14 MeV

_{Difficulties in using Fusion as an energy source :}

_{The conditions of high temperature and pressure are not possible to be maintained on earth. It is difficult to maintain the plasma at the required pressure and temperature, long enough for fusion. It is not feasible as, at present, the energy put in, is more than the energy released. Use of fusion as an energy source may be possible by year 2040.}

_{Scientists all over the world have been working on the fusion problem since the 1930s. The costs of developing a feasible fusion power station are huge.}

_{Advantages of Fusion :}

<sub>Fuel Supply is abundant
Deuterium, can be easily extracted from ordinary water, abundantly available. The surface waters of the earth contain more than millions of tons of deuterium. The tritium required would be produced from lithium, available from land deposits or from sea water. Thus, the fusion fuels are abundantly available and cannot cause any problems.

No Risk of a Nuclear Accident
The amounts of deuterium and tritium in the fusion reaction area will be so small that a large uncontrolled release of energy would be impossible. In the event of malfunction, the plasma would strike the walls of its containment vessel and get cooled. This makes an uncontrollable explosion impossible. Unlike nuclear fission reactions, fusion can be immediately controlled by switching off the fuel supply.

No Air Pollution
Because fuels do not include fossil fuels.

No High-level Nuclear Waste
Fusion power plants do produce radioactive material as high as fission reactors. The radioactive material given out will not remain radioactive for very long.

Conclusion
The raw materials are the main advantage as they are isotopes of Hydrogen and can be derived from water. Fusion could therefore become a renewable energy and absolutely economical source of energy as the fuels are not going to run out.</sub>

_{Fusion in Stars :}

_{Few of the fusion reactions in stars are useful to us practically. These reactions include hydrogen (H), deuterium (D), and tritium (T). The nuclei of all these isotopes contain one proton; the deuterium nucleus has one neutron and the tritium nucleus has two neutrons. Thus, the atom contains 1 electron also.}

_{High temperatures are a pre requisite for fusion. The combination of a deuterium nucleus with one of tritium can occur at the lowest temperature and hence is feasible on earth. The energy emitted is one-fifth in helium-4 nucleus and the majority in the neutron produced.}

_{Solar energy is released due to fusion.}

_{Conditions for Fusion}

Plasma confinement

<sub>Nuclei are positive and normally repel one another. At higher temperature, atoms and nuclei move fast. Their collision supercedes the positive charge and hence fuse. As a result, energy is released. Till now, we have not been able to make a plant which could create and moreover, maintain such conditions.

Temperature
The temperature required for practical uses of fusion is around 100 million degree celsius which is currently impossible to be reached, on earth.

Confinement of fuels
At such tempeartures, the electrons of lighter elements get separated from the atom. A magnetic field can be used to confine the plasma.</sub>

_{See Also :}

Fission
Reactors

_{Related Links :}

_{Science museum, UK
Fusion energy page}

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