Coming in out of the cold: nuclear fusion, for real
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The whole trick with fusion is you've got to get protons close enough together for the strong force to overcome their electrical repulsion and merge them together into a nucleus. The sun does this pretty much by brute force. The sun has over 300,000 times the mass of the Earth, which means there's a lot of gravity weighing down on its core.Skip to next paragraph
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That pressure gets the sun's internal temperature up to several millions of degrees, which means that particles inside the sun's core are flying around at huge velocities. Everything is moving around so fast that protons sometimes get slammed together before their charges have a chance to repel. The strong force takes hold, and a new atom (helium) is born.
In this process, some of the mass of the protons is converted into energy, powering the sun and producing the light that will eventually reach the Earth as sunlight.
Scientists have gotten fusion to occur in the laboratory before, but for the most part, they've tried to mimic conditions inside the sun by whipping hydrogen gas up to extreme temperatures or slamming atoms together in particle accelerators. Both of those options require huge energies and gigantic equipment, not the sort of stuff easily available to build a generator. Is there any way of getting protons close enough together for fusion to occur that doesnt require the energy output of a large city to make it happen?
The answer, it turns out, is yes.
Instead of using high temperatures and incredible densities to ram protons together, the scientists at UCLA cleverly used the structure of an unusual crystal.
Crystals are fascinating things; the atoms inside are all lined up in a tightly ordered lattice, which creates the beautiful structure we associate with crystals. Sometimes those orderly atoms create neat side-effects, like piezoelectricity, which is the effect of creating an electrical charge in a crystal by compressing it. Stressing the bonds between the atoms of some crystals causes electrons to build up on one side, creating a charge difference over the body of the crystal. Other crystals do this when you heat or cool them; these are called pyroelectric crystals.
The new cold fusion experiment went something like this: scientists inserted a small pyroelectric crystal (lithium tantalite) inside a chamber filled with hydrogen. Warming the crystal by about 100 degrees (from -30 F to 45F) produced a huge electrical field of about 100,000 volts across the small crystal.
The tip of a metal wire was inserted near the crystal, which concentrated the charge to a single, powerful point. Remember, hydrogen nuclei have a positive charge, so they feel the force of an electric field, and this one packed quite a wallop! The huge electric field sent the nuclei careening away, smacking into other hydrogen nuclei on their way out. Instead of using intense heat or pressure to get nuclei close enough together to fuse, this new experiment used a very powerful electric field to slam atoms together.
Unlike some previous claims of room-temperature fusion, this one makes intuitive sense: its just another way to get atoms close enough together for the strong force to take over and do the rest. Once the reaction got going, the scientists observed not only the production of helium nuclei, but other tell-tale signs of fusion such as free neutrons and high energy radiation.
This experiment has been repeated successfully and other scientists have reviewed the results: it looks like the real thing this time.
For the time being, don't expect fusion to become a readily available energy option. The current cold fusion apparatus still takes much more energy to start up than you get back out, and it may never end up breaking even. In the mean time, the crystal-fusion device might be used as a compact source of neutrons and X-rays, something that could turn out to be useful making small scanning machines. But it really may not be long until we have the first nuclear fusion-powered devices in common use.
So cold fusion is back, perhaps to stay. After many fits and starts, its finally time for everyday fusion to come in out of the cold.