A multitude of fusion reactions between various nuclei occur within the Sun. Only at the centre of the Sun is the temperature high enough and the density of the plasma great enough for fusion reactions to proceed. This is gravitational confinement of the plasma. The reactions are mainly between Deuterium and Tritium, although others involving helium, carbon, oxygen, and silicon and other elements up to iron participate to a much smaller degree. These higher order reactions are more predominant in red giant stars where temperatures can reach 300 million degrees centigrade.

Power from fusion can be obtained here on Earth by heating a magnetically confined plasma of hydrogen isotopes with a massive electrical discharge in a giant doughnut shaped apparatus, variously called a Stellatron or a Tokomak. The first was called Zeta. In order to obtain a net energy output, it is necessary to get the product of the plasma density, confinement time and plasma temperature to exceed a certain threshold value. To date, an efficiency of only 10% has been attained, and this by using the entire electrical output of one conventional power station. The target of break even is expected to to be fulfilled with future larger machines.

A second approach blasts a tiny glass phial containing tritium with an extremely powerful but short duration laser pulse from every side simultaneously, the idea being to compress the gas thus heating it up to fusion temperature and density. This technique is called inertial confinement as opposed to the magnetic confinement of a Tokomak.

Fusion bombs :-