[jcrites]

One thing which surprised me to learn was the fact that the Sun, per cubic meter, generates about as much power as an active compost heap.

http://en.wikipedia.org/wiki/Sun#Core

The Sun is not like a nuclear bomb going off. It's just a big radiating compost heap. Its huge energy output is due to its large size, and not the intensity of its reaction. (If the Sun's reaction were like a nuclear bomb, the solar system would be destroyed in a supernova-like explosion.)

In other words, nuclear fusion at the Sun's scale isn't very intense a reaction. Why do we expect it's a good idea for a power plant? Do we expect to get significantly hotter than a star? Significantly more dense? It makes sense how nuclear power works. Fusion power, it's not so clear.

Of course, there are fusion bombs as well, but aren't those set off by nuclear bombs?

[neutronicus]

The bulk of the energy release from hydrogen bombs is not generated by fusion. The general design of a hydrogen bomb is that a hydrogen "blanket" surrounds a fission "core". When the fission "core" goes supercritical, it releases enough energy to initiate fusion in the "blanket".

What the "blanket" does at this point is exert pressure on the "core", which would be beginning to blow apart in a conventional nuclear device. Keeping the "core" together for just that small bit of time longer allows it to remain supercritical for just that small bit of time longer, with the energy release growing exponentially with a time constant of 10^-7 seconds.

[queensnake]

How about that - I thought it was all about the binding energy curve: http://ec.europa.eu/research/energy/fi/fi_bs/images/fig2_147...

where, as the diagram shows, fission comes up from the heavier elements (less energy difference) and fusion from the lighter (greatly more).

[neutronicus]

Per fusion event, you get about 14 MeV to the about 200 MeV you get per fission event. It's true that the binding energy per nucleon is higher, but there are many fewer nucleons.