What is fusion?

Fusion is the energy source of the sun and the stars. There are a number of reasons why people pursue fusion. The primary fuel, deuterium, comes from water and is therefore universally available and essentially inexhaustible. There's a very low radiation hazard from fusion and very little proliferation potential. It has a negligible impact on the atmosphere from emissions. In general fusion has high safety and low environmental impact, and everything we know suggests that it will have costs comparable to other energy sources. This paper discusses, in rather general terms, fusion reactions, particularly with deuterium and tritium, and the Tokamak configuration for making fusion