Can someone tell me what self sustaining fusion is?

Answer 1

Fusion that produces enough usable power to produce the conditions for fusion (temperature, containment, velocity, pressure, etc.). The emphasis is on "usable". Most of the energy of a fusion explosion (the result of "inertial confinement") is not recoverable because of structural limitations. Neutron containment and structure-fatigue problems also contribute to the difficulty of using continuously produced energy.
A "break-even" reactor still has enormous issues of heat dissipation, since all the fission energy remains at the site. The ref. considers a produced/consumed ratio of 20 a practical value for output of significantly more energy than that used for fusion.

Answer 2

In order for fusion to occur we have to heat a hydrogen plasma up to temperatures of 100,000,000 C. That's hot ... extremely hot. And like all hot things that plasma is going to want to cool down, and reach room temperature. At the same time fusion will be going on inside the plasma and it will be releasing energy into the plasma.

If the amount of heat created by fusion is greater than or equal to the amount of heat lost by the plasma trying to cool down, then we say that the fusion reaction is self sustaining, and the fusion reaction will continue on its own.

On the other hand, if the heat created by fusion is less than the heat lost by cooling, then the plasma will start to cool, and with out some other means of heating the plasma, eventually the fusion reaction will stop.

Answer 3

Ya, what he said. Self-sustaining means that the reaction will continue after you remove the energy used to get it started. Sort of like a fire with wet logs; they aren't much good if you have to keep relighting them.