What is Nuclear Fusion?

Normal matter (stuff) is made up of atoms. These atoms (normally) are made up of protons (positive particles) and neutrons (neutral particles) in a "nucleus", and surrounded by electrons (negative particles). The negative particles repulse other negative particles, while attracting positive particles. The positive particles act in the opposite manner.

In nuclear fusion, very high temperature and pressure are used to squeeze nuclei together. When done to lighter elements (hydrogen - 1 proton, and boron - 5 protons, are favorites), energy is released.

Nuclear fusion holds great potential for cheap, plentiful energy. Hydrogen and boron are very plentiful fuel sources. It is not free from radioactive concerns. Different forms of fusion involve different amounts of radioactive materials (inputs and byproducts). Some are somewhat higher than current fission reactors. Some are less.

The sun is an existence proof for fusion power. There, huge pressure is available due to gravity (the hydrogen is compressed to 150,000 kg/m^3). This allows fusion to occur at a relatively low temperature - 13.6 million degrees. At this temperature, the hydrogen gas becomes "plasma" - the fourth state of matter (after solid, liquid, and gas). In a plasma, the electrons are separated from their nuclei, and the whole thing can be manipulated using electromagnetic fields (very convenient for us).

A typical commercial power planet produces around 1 gigawatt (1 billion watts). Using fusion as the sun does would require 170 billion tons of hydrogen, in a cube-shaped reactor 1 mile on a side (and it would have to sustain the enormous pressure and heat of the sun).

Obviously, some innovation is required to make fusion power work here on Earth. The most promising current projects are:

1. Tokamak - this is the most well funded type of project. A big donut-shaped container, surrounded by magnets, is used to hold the fusion plasma.
2. Laser inertia - powerful lasers push two nuclei together directly. This is how fusion bombs work.
3. Polywell - this design was championed by Robert Bussard (of Bussard ramjet fame). Unfortunately, Dr. Bussard died recently. The project is continuing without him.