Fusion Basics

Fusion is the process of joining two atomic nuclei together to form a single large one. The simplest reaction of this kind is that of hydrogen nuclei into helium. This is the reaction that powers our sun and provides the world with its heat and light. Fusion is a surprisingly easy reaction to cause for its awesome nature and it is also a surprisingly difficult reaction to master for its ease of intialization. A simple iec (inertial electrostatic containment) device called the hirsch fusor is capable of causing the reaction. This machine is simple enough to be built by most people but is completely incapable of causing any fusion reaction that would be useful for the production of energy. If you are interested in this device i suggest that you visit fusor.net which has a good amount of information on this device.

More conventionally fusion research is confined to two fields magnetic restriction and inertial confinement. The first of these two types represents the fusion reactor in its most dramatic form. A huge toroidal chamber surrounded by a molten lithium blanket and dozens of huge superconducting magnets capable of creating fields on the order of tens of thousands of gauss. This is the tokamak. To understand how tokamaks work it is first necessary to know something about the basic physics of fusion.

The fusion reaction is governed by the laws of quantum mechanics and in a collision between two particles there is a certain probability that the two particles nucleuses will become close enough to each other to fuse together. In the collisions that happen at everyday energies and pressures this probability is phenominally low and the number of fusions going on is to low to measure for most of the time. However as temperature and pressure rises the energies of the collisions increase and the nucleuses of atoms are pushed closer together increasing the probability that they will fuse. The frequency with which this fusion reaction occurs for a particular material at a specific pressure and temperature is what is called the cross section.

A favorable cross section must be acchieved by keeping continually extremely high temperatures in the reaction chamber. This is accomplished in the sun by sheer bulk and the insulation of the suns core is made of millions of meters of hydrogen gas. This kind of isulation is obviously not possible on earth especially considering that anything that comes into contact with such high temperatures is likely to vaporize. The insulation that a machine has is called its energy confinement time. Which is defined more precisely as the amount of time it takes the plasma temperature to drop to 1/e its original value. Very low energy confinement times have been acchieved in tokamaks by confining the most energetic particles inside the plasma by using extremely strong magnetic fields. Then they surround the chamber with a blanket of liquid lithium metal.