Science Forums 2

[CraigD]

Originally Posted by Gardamorg

But unlike Antimatter, after a certain point in time, a large enough self sustaining fusion reactor doesn't require any fuel, and it's energy production will eventually achieve greater energy than Antimatter Annihilation, and it will continue to achieve even greater amounts of energy after that.

Wherever did you get these idea, Gardamorg?!

Nuclear fusion produces energy by transforming elements with low atomic numbers (eg: hydrogen, atomic number 1) into ones with higher atomic numbers (eg: helium, atomic number 2) The slight difference in mass between the beginning and end product (eg: ) results in energy, according to the famous old equation , where in this case is the difference in mass between the beginning and end products.

A fusion reactor needs fuel, in the form of low atomic number elements. What’s meant by “self sustaining” is not that the reactor doesn’t need fuel, but that it doesn’t need an outside source of energy to run, either more energy than it produces (an “under unity” reactor) or less (an “over unity” reactor, the goal of fusion power research). So far, all man-made fusion reactions have either been under unity (various experimental “controlled fusion” reactors, or fusion bombs, which produce much more energy than that of the explosives and fission bombs used to cause the fusion reaction, but are very destructive and difficult to harness for such things as electric power generation or spacecraft propulsion.

An ideal fusion reactor could use the end product of one fusion reaction (eg: ) as fuel for another (eg: ). Once a fusion reaction has produced nickel (atomic number 56), it’s impossible to use the end product to generate more energy, as the next fusion reaction produces end products that mass slightly more than their beginning. Such reactions are seen only in stars, which are in a sense ideal fusion reactors.