At dinner, this evening, I was speaking with one of the Wadham College fellows about nuclear fusion. He highlighted an element that I hadn’t previously heard discussed: namely the fact that you need to build truly enormous reactors so as to have a surface area to volume ratio low enough that fusion can be sustained. He spoke of the possibility that two or three gargantuan power plants could serve areas as vast as Europe or North America, but that enormous technical hurdles remain, most of them relating to plasma control.
Remember that, once atoms form a plasma, they have been stripped of their electrons. As such, the positive charges of all protons cause them to repel one another with a force inversely proportional to the square of the distance between them. Imagine trying to push the north poles of two powerful bar magnets together, and you will begin to appreciate the kind of force dynamics at work. For fusion to be attained, that repulsion needs to be overcome. In the kind of reactors being experimentally constructed now, that is generally achieved through containment using extremely powerful electromagnets.
Under construction now, in France, is the International Experimental Thermonuclear Reactor (ITER). Construction will finish around 2016 and the device will hopefully provide the information and experience required to develop fusion reactors commercially. If they could be deployed, they would offer the benefits of existing fission plants (reliable and substantial electrical generation), with relatively few issues relating to radiactivity (though, as the fellow pointed out, the gamma rays generated in hydrogen fusion would cause the reactors themselves to become quite radioactive, over time).
The possibility of a deus ex machina stepping in to deal with energy security and climate change is certainly an alluring one. With enough power, it would be possible to produce as much hydrogen as you could desire from water. If gargantuan plants are the mechanism to make fusion feasible, energy from them could be partially distributed in that way. Even if fusion were not a panacea, it could be an important component in a response that also includes conservation, the development of renewables, and technical mechanisms to make fossil fuel use carbon neutral.
I don’t know nearly enough about nuclear physics to be able to comment on the viability of fusion as a power source. One thing you hear constantly in journalistic coverage of it is that it has been twenty years or so off for ages now. Hopefully, with the lessons learned from ITER, it will be a real twenty years this time. If that did come to pass, it would certainly not be too soon. On a political note, it is probably a good thing it is being built in France. When it (inevitably) goes way over-budget, the government is reasonably unlikely to scrap the project. By way of comparison, recall how the US government cancelled the Superconducting Super Collider in 1993, after the expected cost tripled to US$12 billion.