Fusion is the fusing together of two small nuclei to produce a bigger nucleus and release a lot of energy in the process.
Fusion is the nuclear reaction that takes place in the stars!
There are many good sites that explain what happens. Take a look at this one.
The basic Hydrogen fusion cycle that occurs within a star involves four hydrogen nuclei (protons) and two electrons and yields a Helium nucleus, two neutrinos and six photons.
This process occurs in three steps:
Note that steps 1 and 2 each happen twice for each time step 3 occurs. In this process the total net energy released is about 26 MeV
Here on earth, fusion research is aimed at demonstrating that this energy source can be used to produce electricity in a safe and environmentally benign way.
Very high temperatures and pressures are required to overcome the repulsion between nuclei of the isotopes of hydrogen that fuse together. Once the repulsion is overcome the fused products of the nuclear reaction have a higher binding energy per nucleon (an 'A' Level study topic) than the reactants, making the reaction energetically viable and producing a release of energy.
ITER is a joint international research and development project that aims to demonstrate the scientific and technical feasibility of fusion power. The partners in the project - the ITER Parties - are the European Union (represented by EURATOM), Japan, the People´s Republic of China, India, the Republic of Korea, the Russian Federation and the USA. ITER will be constructed in Europe, at Cadarache in the South of France.
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