Two Important Fusion Reactions
D + T => He-4 + n
For first generation fusion reactors
The "D-T" reaction has the highest reaction rate at the plasma temperatures which are currently achievable; it also has a very high energy release. These properties make it the easiest reaction to use in a man-made fusion reactor. As the figure shows, the products of this reaction include an alpha particle (Helium-4 nucleus) with 3.5 MeV energy, and a neutron with 14.1 MeV energy. The neutron escapes from the plasma (it has no charge and is not confined) and can be trapped in a surrounding "blanket" structure, where the n + Li-6 => He-4 + T reaction can be used to "convert" the neutrons back into tritium fuel.
- 1 eV = 1.6022E-19 joules;
- Average particle thermal kinetic energy is 1 eV per 11,600 K.
"P-P": Solar Fusion Chain
Known as the proton-proton chain, the reaction process depicted above is the dominant fusion mechanism in light stars, including our sun. (In heavier stars, a more complicated process known as the carbon cycle predominates.) In the P-P chain, two pairs of protons fuse, forming two deuterons. Each deuteron fuses with an additional proton to form helium-3. The two helium-3 nuclei which then fuse to create beryllium-6, which is unstable and disintegrates into two protons plus a helium-4 (alpha particle). In addition, the process releases two neutrinos, two positrons, and gamma rays. The positrons annihilate quickly with electrons in the plasma, releasing additional energy in the form of gamma rays. The neutrinos interact so weakly that they fly right out of the sun immediately.
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