1. What is Fusion ?

Nuclear Fusion is the process powering the Sun and stars. In the core of the Sun, at temperatures of 10-15 million Kelvin, Hydrogen is converted to Helium by fusion - providing enough energy to keep the Sun burning - and to sustain life on Earth.

A vigorous world-wide research programme is underway, aimed at harnessing fusion energy to produce electricity on Earth. If successful, this will offer a viable alternative energy supply within the next 30-40 years - with significant environmental, supply and safety advantages over present energy sources (See section 6).

To harness fusion on Earth, different, more efficient fusion reactions than those at work in the Sun are chosen - those between the two heavy forms of Hydrogen : Deuterium (D) and Tritium (T). All forms of Hydrogen contain one proton and one electron. Protium, the common form of Hydrogen has no neutrons, Deuterium has one neutron, and Tritium has two. If forced together, the Deuterium and Tritium nuclei fuse and then break apart to form a helium nucleus (two protons and two neutrons) and an uncharged neutron. The excess energy from the fusion reaction (released because the products of the reaction are bound together in a more stable way than the reactants) is mostly contained in the free neutron.

Fusion occurs at a sufficient rate only at very high energies (temperatures) - on earth, temperatures greater than 100 million Kelvin are required. At these extreme temperatures, the Deuterium - Tritium (D-T) gas mixture becomes a plasma (a hot, electrically charged gas). In a plasma, the atoms become separated - electrons have been stripped from the atomic nuclei (called the "ions"). For the positively charged ions to fuse, their temperature (or energy) must be sufficient to overcome their natural charge repulsion.

In order to harness fusion energy, scientists and engineers are learning how to control very high temperature plasmas. The use of much lower temperature plasmas are now widely used in industry, especially for semi-conductor manufacture. However, the control of high temperature fusion plasmas presents several major science and engineering challenges - how to heat a plasma to in excess of 100 million Kelvin and how to confine such a plasma, sustaining it so that the fusion reaction can become established.