As you may remember from high school science class, all matter is comprised of small units called atoms. Atoms themselves are made up of three kinds of smaller particles: Protons (with a positive charge), Neutrons (with no charge), and Electrons (with a negative charge). The protons and neutrons are concentrated in a very small and dense region of the atom known as the nucleus. This is the region we will be focusing on from here on in, hence the word nuclear. The number of protons in the nucleus is called the "atomic number" or "Z" and it determines what element the atom belongs to. Any given element will always have the same number of protons, but the number of neutrons can vary. Two atoms with the same atomic number (i.e. of the same element), but with a different number of neutrons are called isotopes. The sum of the number of protons and neutrons in any given isotope is known as the atomic mass.

When it comes to fusion, we are only concerned with the first few elements on the periodic table, mainly Hydrogen (H) and Helium (He). Furthermore, we are interested in two specific isotopes of hydrogen, called Deuterium and Tritium.

A simplified diagram of the atom

Fig. 2: The isotopes of hydrogen (image from Encarta Encyclopedia)

Deuterium and Tritium are chemically identical to normal Hydrogen (Protium); the only difference is that they have atomic masses of 2 and 3, respectively (protium has an atomic mass of 1).

Deuterium occurs naturally in the form of "heavy water," a substance almost identical to normal water, except that it has a formula of D₂O, instead of H₂O. It can be easily extracted from the oceans using common chemical processes.

Tritium is radioactive and does not occur in nature due to its short half life of 12 years. It must be made in nuclear reactors by bombarding lithium with neutrons. As you will see below, however, Tritium produces very energetic fusion reactions when it reacts with Deuterium. It is also the easiest isotope of hydrogen to undergo fusion.

1. D + D → T(1.01 MeV) + p(3.02 MeV)

2. D + D → He3(0.82 MeV) + n(2.45 MeV)

3. D + T → He4(3.5 MeV) + n (14.1 MeV)

4. D + He3 → He4(3.6MeV) + p(14.7 MeV)

5. T + T → He4 + 2 n + (11.3 MeV)

6. p + B11 → 3 He4 + (8.7 MeV)

D: Deuterium

p: Proton, normal hydrogen

He: Helium

T: Tritium

n: neutron

As mentioned before, fusion is the process of "fusing" two light nuclei together to form a heaver atom. As an example, we will use the fusion of two Deuterium atoms.

Alone, by themselves, two Deuterium atoms have more mass than a single Helium atom. So, when we fuse two of them together to make Helium, some of that mass gets lost. More specifically, it gets converted into energy. This is where Einstein's famous equation, E=mc² comes into play. The tiny amount of mass that is lost in the reaction gets converted into a huge amount of energy, which is released in the form of fast moving particles.

As you can see, the energy released in a fusion reaction is quite large, a million times greater than what you would get out of the best chemical reactions. However, a certain amount of seed energy is required in order to make the reaction take place. This seed energy is often on the order of 20 KeV or greater. As mentioned in the brief note above, you multiply the energy in eV by 11,800 to get the temperature in degrees Kelvin. This is why people say that fusion requires temperatures of 200 million degrees to take place. In order to get the fusion reaction to "ignite" and burn like a fire, the energy released in the reaction must go back into creating that "seed energy." If too much of the fusion energy is lost, then the reaction will cease once the seed energy disappears.

Once you can ignite a self-sustaining reaction, then it is simply a matter of supplying fuel and extracting the energy. In the reactions where neutrons are produced, you surround the reaction with a blanket of water or liquid Lithium. This will slow down the neutrons and produce heat, which would then be used to boil water, make steam and drive turbines. In the case of Lithium, this will also produce more Tritium for use as fusion fuel. Unfortunately, this process of heating and boiling water is only about 30% efficient. Steam technology is over 100 years old, and it seems a bit strange to be using such antiquated techniques with such an advanced power source.

The best way around this problem is to pick a reaction in which the reaction products are charged particles (like protons and Helium nuclei). These particles can be collected on a grid and converted directly into electricity with 90% efficiency or better. Reactions 4 and 6 are examples of this.  

To see examples of how fusion is currently done in nature and by artificial means, go on to the next section.