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Over the past 15 years, enthusiasts have generated some 3,000 manuscripts on cold fusion, but very few were ever published in scientific journals. Many results evaporated under outside examination, and promoters pushed “free energy” schemes that sounded more like perpetual motion than physics. Most of those manuscripts “are not helpful,” says Hagelstein, a theorist with wide-ranging interests in optics, energy, and nuclear physics. But some 50 do show interesting, reproducible effects. “The heat effect has been replicated many times,” Hagelstein. It works only when deuterium is loaded into palladium cells, and never when normal hydrogen is used instead of the heavy isotope. Exacting measurements with heat-measurement instruments have answered criticisms of the original experiments. Excess heat has been measured beyond what Hagelstein considers any reasonable doubt.

Experiments that produce excess heat also have yielded helium-4, one potential product of the fusion of two deuterium nuclei, in amounts that correlate with the excess heat. Theory predicts that the fusion reaction should generate 24 million electron volts (MeV) of energy per helium-4 nucleus. An analysis by Michael McKubre of SRI International detected energy of 31 MeV- a match within the experimental uncertainty of plus or minus 13 MeV. Skeptics had doubted the reaction was possible, but Hagelstein says McKubre’s analysis of the experiments, reported at last year’s cold fusion meeting, shows that fusion of two deuterium to yield helium-4 “is not as nutty as it initially seemed.”

McKubre has also found that the seeming inconsistency in experimental heat production arose from differences in the amount of deuterium packed into the palladium electrode. Whenever the number of deuterium atoms loaded into the metal matched or exceeded the number of palladium atoms, excess heat was generated. Palladium loaded with slightly less deuterium produced inconsistent results, and if the deuterium level was reduced by a great amount, then no excess heat at all was produced. Deuterium loading was hard to control and limited by the strength of the metal. Unfortunately, palladium strength is difficult to predict or control, and is not improved by purification; indeed, the purest palladium ruptured at lower loadings, and the highest strength was seen only in one impure batch.

The growing evidence has convinced fusion physicist George Miley of the University of Illinois at Urbana-Champaign that “there are important physical phenomena occurring.” Skeptics aren’t changing their minds, but he thinks that previously neutral observers are becoming more receptive to the possibility that a real phenomenon is occurring in these experiments. Yet while cold fusion researchers have gone from thinking they smell smoke to feeling warmth, it’s still not clear what’s really going on. “This field is led experimentally. We’ve got to get the theories up to where they start helping lead the experiments,” Miley says.

The challenge for theorists like Hagelstein is to fill the yawning gap between traditional nuclear theory and cold fusion experiments. He suspects the difficulty lies with “a very powerful approximation” at the root of 70 years of nuclear physics-that all nuclear interactions occur between two particles in a vacuum. He thinks that assumption breaks down in cold fusion, where the interacting particles are tightly packed in a metal lattice. His idea is that the deuterium nuclei exchange vibrational energy, or “phonons,” with the surrounding palladium atoms. That exchange could enhance nuclear interactions that would otherwise be vanishingly small, so that the reactions can occur at the rates implied by cold fusion experiments. Hagelstein’s theory is still in development, but is reaching a point where he can start making testable predictions-a vital step toward making cold fusion a credible science. “In time, hopefully, we’ll get more of the puzzle figured out,” he says.

A positive Department of Energy review would open the door to badly needed research support, but big questions remain even if the reality of the physics can be established. Is the cold fusion effect strong enough to be used for practical energy production? If it is, it’s not likely to compete directly with hot fusion, says Miley, who works on both. Cold fusion works on a small scale, so it might find a home in small distributed power units. Hot fusion’s natural home is inside the sun; if it can be controlled on our planet, it would be inside large reactors feeding power into the grid.

But those goals are a long ways off. For now, the little community of cold-fusion researchers hopes it is on the threshold of validation after 15 years of struggle.

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