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Ahead Warp Factor...One-Half?

© Robert Davis

I've been following research into controlled nuclear fusion for a number of years, and am convinced that it holds out the highest promise of being a clean, renewable, and all but limitless source of energy for human civilization. I am also deeply interested in it from the standpoint of advanced space propulsion; faster-than-light travel is pretty farfetched (though "never" is a terribly strong word, and one that you won't hear pass my lips on this issue), but an engine that could open up travel across the solar system without requiring us to rewrite the physics books is still pretty darned exciting, itself.

Nuclear fusion, of course, is the reaction that powers the sun. Where fission is the division of heavy nuclei, fusion is the combination of light ones. The sun is merrily fusing hydrogen into helium and releasing enormous quantities of energy in the process--for which I'm sure we all on earth are very thankful.

The big challenge, for those of us who would like to duplicate this incredibly useful reaction on earth, is to achieve ignition; that is, the fusion reaction must be sustainable such that more energy (significantly more) comes out of it than is going in. Steady, if incremental, progress has been made for years on this problem, and negotiations continue in order to agree upon a site for the next international research reactor, a $5 billion project called ITER. At one time this stood formally for "International Thermonuclear Experimental Reactor", but anymore the fashion is to note that "iter" means "the way" in Latin and to leave it at that.

There are essentially two approaches to controlled nuclear fusion. Inertial confinement fusion involves firing a large number of convergent, high-energy lasers at a tiny pellet of fuel--for example, an isotope of hydrogen called deuterium--in order to compress and heat it to the point of ignition. Basically, you're using lasers to make minuscule stars. The other, thermonuclear fusion, involves using magnetic fields to contain hydrogen plasma--perhaps a combination of two isotopes of hydrogen, deuterium and tritium--while continuing to increase the plasma's temperature to the point of ignition.

The magnetic confinement approach of the thermonuclear reactor seeks to increase the time during which ions in the plasma are in close proximity to each other (their high energy sends them careening all over the place, which is not exactly what we're after), increasing the likelihood of a fusion reaction. The inertial confinement strategy is simply to hit the fuel so hard and fast that it has no time to do anything but go ahead and fuse.

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