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Cold fusion is the concept of a nuclear fusion reaction occurring at conditions near room temperature and atmospheric pressure with a net release of energy (in contrast to, e.g. a neutron generator, in which low-efficiency fusion is induced to produce high-energy particles).

The idea was brought into public consciousness by an announcement made in 1989 by the chemists Stanley Pons and Martin Fleischmann at the University of Utah that they had generated excess heat that could only be explained by the occurrence of a nuclear reaction. They had used only a very simple process: a pair of electrodes immersed in heavy water. Early attempts to replicate the effect were unsuccessful, after which cold fusion gained a reputation as an example of pathological science.

The United States Department of Energy convened a panel to investigate their claims.^[1] This and a second panel of 2004 did not find the evidence convincing enough to justify a federally-funded program.^[2] Also in 2004, a review report by Physics Today described most scientists as deeply skeptical,^[3] while noting "the existence of a small and devoted coterie of researchers who continue to investigate the alleged effect."

According to cold fusion advocates there are now nearly 200 published reports of anomalous power and over 60 of anomalous tritium production.^[4] While most of these reports have appeared only in non-mainstream publications, a few have been also been published in peer-reviewed journals.^[5]

Contents 1 History of cold fusion by electrolysis 1.1 Early work 1.2 Pons and Fleischmann's experiment 1.3 Experimental set-up and observations 1.4 Continuing efforts 2 Arguments in the controversy 2.1 Reproducibility of the result 2.2 Current understanding of nuclear process 3 Other kinds of fusion 3.1 Locally cold fusion 3.2 Generally cold, locally hot fusion 3.3 Hot fusion 4 References 5 See also 6 Further information 6.1 Books 6.2 External links

The subject has been of scientific interest since nuclear fusion was first understood. Hot nuclear fusion using deuterium yields large amounts of energy, uses an abundant fuel source, and produces only small amounts of manageable waste. If this could be achieved at a lower temperature then a major new source of renewable energy would have been found.

The idea that palladium or titanium might catalyze fusion stems from the special ability of these metals to adsorb large quantities of hydrogen (including its deuterium isotope), the hope being that deuterium atoms would be close enough together to induce fusion at ordinary temperatures. The special ability of palladium to adsorb hydrogen was recognized in the nineteenth century. In the late nineteen-twenties, two German scientists, F. Paneth and K. Peters, reported the transformation of hydrogen into helium by spontaneous nuclear catalysis when hydrogen is adsorbed by finely divided palladium at room temperature. These authors later acknowledged that the helium they measured was due to background from the air.

In 1927, Swedish scientist J. Tandberg said that he had fused hydrogen into helium in an electrolytic cell with palladium electrodes. On the basis of his work he applied for a Swedish patent for "a method to produce helium and useful reaction energy". After deuterium was discovered in 1932, Tandberg continued his experiments with heavy water. Due to Paneth and Peters' retraction, Tandberg's patent application was eventually denied.

The term "cold fusion" was coined by Dr Paul Palmer of Brigham Young University in 1986 in an investigation of "geo-fusion", or the possible existence of fusion in a planetary core.

On March 23, 1989, the chemists Stanley Pons and Martin Fleischmann at the University of Utah held a press conference and reported the production of excess heat that could only be explained by a nuclear process. The report was particularly astounding given the simplicity of the equipment, just a pair of electrodes connected to a battery and immersed in a jar of heavy water (dideuterium oxide). The press reported on the experiments widely, and it was one of the front-page items on most newspapers around the world. The immense beneficial implications of the Utah experiments, if they were correct, and the ready availability of the required equipment, led scientists around the world to attempt to repeat the experiments within hours of the announcement.

The press conference followed about a year of work of increasing tempo by Pons and Fleischmann, who had been working on their basic experiments since 1984. In 1988 they applied to the US Department of Energy for funding for a larger series of experiments: up to this point they had been running their experiments "out of pocket".

The grant proposal was turned over to several people for peer review, including Steven Jones of Brigham Young University. Jones had worked on muon-catalyzed fusion for some time, and had written an article on the topic entitled Cold Nuclear Fusion that had been published in Scientific American in July 1987. He had since turned his attention to the problem of fusion in high-pressure environments, believing it could explain the fact that the interior temperature of the Earth was hotter than could be explained without nuclear reactions, and by unusually high concentrations of helium-3 around volcanoes that implied some sort of nuclear reaction within. At first he worked with diamond anvils, but had since moved to electrolytic cells similar to those being worked on by Pons and Fleischmann, which he referred to as piezonuclear fusion. In order to characterize the reactions, Jones had spent considerable time designing and building a neutron counter, one able to accurately measure the tiny numbers of neutrons being produced in his experiments.

Both teams were in Utah, and met on several occasions to discuss sharing work and techniques. During this time Pons and Fleischmann described their experiments as generating considerable "excess energy", excess in that it could not be explained by chemical reactions alone. If this were true, their device would have considerable commercial value, and should be protected by patents. Jones was measuring neutron flux instead, and seems to have considered it primarily of scientific interest, not commercial. In order to avoid problems in the future, the teams apparently agreed to simultaneously publish their results, although their accounts of their March 6th meeting differ.

In mid-March both teams were ready to publish, and Fleischmann and Jones were to meet at the airport on the 24th to both hand in their papers at the exact same time. However Pons and Fleischmann then "jumped the gun", and held their press conference the day before. Jones, apparently furious at being "scooped", faxed in his paper to Nature as soon as he saw the press announcements. Thus the teams both rushed to publish, which has perhaps muddied the field more than any scientific aspects.

Within days scientists around the world had started work on duplications of the experiments. On April 10th a team at Texas A&M University published results of excess heat, and later that day a team at the Georgia Institute of Technology announced neutron production. Both results were widely reported on in the press. Not so well reported was the fact that both teams soon withdrew their results for lack of evidence.^[6][7] For the next six weeks competing claims, counterclaims, and suggested explanations kept the topic on the front pages, and led to what writers have referred to as "fusion confusion."

On April 12 Pons received a standing ovation from at the semi-annual meeting of the American Chemical Society.^[8] However, several weeks later at the meeting of the American Physical Society on May 1 there was a session on cold fusion at which a series of failed experiments were reported.^[9] The mainstream press reported these negative findings.^[7]

Both critics and those attempting replications were frustrated by what they said was incomplete information released by the University of Utah. With the initial reports suggesting successful duplication of their experiments there was not much public criticism, but a growing body of failed experiments started a "buzz" of their own. Pons and Fleischmann later apparently claimed that there was a "secret" to the experiment^{[citation needed]}, a statement that infuriated the majority of scientists to the point of dismissing the experiment out of hand.

By the end of May much of the media attention had faded. William Happer said:"The furor died down and the enthusiasm for supporting the research ebbed as weeks and months went by and many laboratories reported that they could not reproduce the results of Pons and Fleischman and other embarrassed laboratories withdrew hasty but mistaken confirmations of their results." ^[10] However, while the research effort also cooled to some degree, projects continued around the world.

In their original set-up, Fleischmann and Pons used a Dewar flask (a double-walled vacuum flask) for the electrolysis, so that heat conduction would be minimal on the side and the bottom of the cell (only 5 % of the heat loss in this experiment). The cell flask was then submerged in a bath maintained at constant temperature to eliminate the effect of external heat sources. They used an open cell, thus allowing the gaseous deuterium and oxygen resulting from the electrolysis reaction to leave the cell (with some heat too). It was necessary to replenish the cell with heavy water at regular intervals. The cell did not contain a stirring apparatus, though the authors claimed that the bubbling action of the gas kept the electrolyte well mixed and of a uniform temperature. The efficacy of this stirring method and thus the validity of the temperature measurements would later be disputed.^[7] Special attention was paid to the purity of the palladium cathode and electrolyte to prevent the build-up of material on its surface, especially after long periods of operation.

The cell was also instrumented with a thermistor to measure the temperature of the electrolyte, and an electrical heater to generate pulses of heat and calibrate the heat loss due to the gas outlet. After calibration, it was possible to compute the heat generated by the reaction.

A constant current was applied to the cell continuously for many weeks, and heavy water was added as necessary. For most of the time, the power input to the cell was equal to the power that went out of the cell within measuring accuracy, and the cell temperature was stable at around 30 °C. But then, at some point (and in some of the experiments), the temperature rose suddenly to about 50 °C without changes in the input power, for durations of 2 days or more. The generated power was calculated to be about 20 times the input power during the power bursts. Eventually the power bursts in any one cell would no longer occur and the cell was turned off.

Japan has instituted the largest research program to date on the topic. After spending $20 million from 1992 to 1997 on a focused research effort, their program ended with the announcement that "We couldn't achieve what was first claimed in terms of cold fusion."^[11]

In 1994, Dr. David Goodstein described the field as follows:^[12]

"Cold Fusion is a pariah field, cast out by the scientific establishment. Between Cold Fusion and respectable science there is virtually no communication at all. Cold fusion papers are almost never published in refereed scientific journals, with the result that those works don't receive the normal critical scrutiny that science requires. On the other hand, because the Cold-Fusioners see themselves as a community under siege, there is little internal criticism. Experiments and theories tend to be accepted at face value, for fear of providing even more fuel for external critics, if anyone outside the group was bothering to listen. In these circumstances, crackpots flourish, making matters worse for those who believe that there is serious science going on here."

Brian Josephson and other cold fusion researchers said that cold fusion is suppressed, and that skeptics suffer from pathological disbelief.^[13] They said that there is virtually no possibility for funding in cold fusion in the United States, and no chance of getting published.^[3] They said that people in universities refuse to work on it because they would be ridiculed by their colleagues.^[14]

There are still a number of people researching the possibilities of generating power with cold fusion. Scientists in several countries continue the research, and meet at the International Conference on Cold Fusion.

The cold fusion researchers presenting their review document to the 2004 DoE panel on cold fusion said that the observation of excess heat has been reproduced, that it can be reproduced at will under the proper conditions, and that many of the reasons for failure to reproduce it have been discovered. Despite the assertions of these researchers, most reviewers stated that the effects are not repeatable.

In 1989, the DoE panel said: "Even a single short but valid cold fusion period would be revolutionary. As a result, it is difficult convincingly to resolve all cold fusion claims since, for example, any good experiment that fails to find cold fusion can be discounted as merely not working for unknown reasons."^[15]

Cold fusion's most significant problem in the eyes of many scientists is that current theories describing conventional "hot" nuclear fusion cannot explain how a cold fusion reaction could occur at relatively low temperatures, and that there is currently no accepted theory to explain cold fusion.^[16][17] The 1989 DoE panel said: "Nuclear fusion at room temperature, of the type discussed in this report, would be contrary to all understanding gained of nuclear reactions in the last half century; it would require the invention of an entirely new nuclear process", but it also recognized that the lack of a satisfactory explanation cannot be used to dismiss experimental evidence.^[18]

Cold fusion observations are contrary to the conventional physics of nuclear fusion in several ways :

• Nuclear reaction in general: The average density of atoms in the palladium rod seems vastly insufficient to force pairs of nuclei close enough for fusion to occur according to mechanisms known to mainstream theories. The average distance is approximately 0.17 nanometers, a distance at which the attractive strong nuclear force cannot overcome the Coulomb repulsion. Actually, deuterium atoms are closer together in D2 gas molecules, which do not exhibit fusion.

• Deuterium fusion products: if the excess heat were generated by the fusion of 2 deuterium atoms, the most probable outcome would be the generation of either a tritium atom and a proton, or a ³He and a neutron. The level of neutrons, tritium and ³He actually observed in Fleischmann-Pons experiment have been well below the level expected in view of the heat generated, implying that these fusion reactions cannot explain it. If the excess heat were generated by the hot fusion of 2 deuterium atoms into ⁴He, a reaction which is normally extremely rare, gamma rays and helium would be generated. Again, insufficient levels of helium and gamma rays have been observed to explain the excess heat.

• Conversion to heat: there is no known mechanism that would release fusion energy as heat instead of radiation within the relatively small metal lattice^[12]. Robert F. Heeter said that the direct conversion of fusion energy into heat is not possible because of energy and momentum conservation and the laws of special relativity.^[19]

Cold fusion theoreticians have proposed various speculative theories to explain the reported observations. Such ideas run counter to mainstream physical theories and associated observational evidence.^[4]

Some other kinds of fusion may be termed "cold" in some sense but are separate from the cold fusion controversy. "Cold" may be taken in the sense that no part of the reaction is actually hot (except for the reaction products), or that the energies required are low and the bulk of the material is at a relatively low temperature. Some other kinds of fusion are "hot", involving reactions which create macroscopic regions of very high temperature and pressure.

• Muon-catalyzed fusion is a well-established and reproducible fusion process which occurs at low temperatures. It has been studied in detail by Steven Jones in the early 1980s. Because of the energy required to create muons, it is not able to produce net energy.

• In cluster impact fusion, microscopic droplets of heavy water (on the order of 100-1000 molecules) are accelerated to collide with a target, so that their temperature at impact reaches at most 10⁵ kelvin, 10,000 times smaller than the temperature required for hot fusion. In 1989, Friedlander and his coworkers observed 10¹⁰ more fusion events than expected with standard fusion theory. Recent research ([11]) suggests that the calculation of effective temperature may have failed to account for certain molecular effects which raise the effective collision temperature, so that this is a microscopic form of hot fusion.

• In sonoluminescence, acoustic shock waves create temporary bubbles that collapse shortly after creation, producing very high temperatures and pressures. In 2002, Rusi P. Taleyarkhan explored the possibility that bubble fusion occurs in those collapsing bubbles. If this is the case, it is because the temperature and pressure are sufficiently high to produce hot fusion.

• The Farnsworth-Hirsch Fusor is a tabletop device in which fusion occurs. This fusion comes from high effective temperatures produced by electrostatic acceleration of ions. The device can be built inexpensively, but it too is unable to produce a net power output.

• Antimatter-catalyzed fusion uses small amounts of antimatter to trigger a tiny fusion explosion. This has been studied primarily in the context of making nuclear pulse propulsion feasible.

Several of these systems are "nonequilibrium systems", in which very high temperatures and pressures are produced in a relatively small region adjacent to material of much lower temperature. In his doctoral thesis for Massachusetts Institute of Technology, Todd Rider did a theoretical study of all non-equilibrium fusion systems. He demonstrated that all such systems will leak energy at a rapid rate due to Bremsstrahlung, radiation produced when electrons in the plasma hit other electrons or ions at a cooler temperature and suddenly decelerate. The problem is not as pronounced in a hot plasma because the range of temperatures, and thus the magnitude of the deceleration, is much lower.

• "Standard" fusion, in which the fuel reaches tremendous temperature and pressure inside a fusion reactor, nuclear weapon, or star.

• Alchemy
• Transmutation
• Pathological science
• Protoscience

• Close, Frank E..Too Hot to Handle: The Race for Cold Fusion. Princeton, N.J. : Princeton University Press, 1991. ISBN 0-691-08591-9; ISBN 0-14-015926-6.
• Huizenga, John R. Cold Fusion: The Scientific Fiasco of the Century. Rochester, N.Y.: University of Rochester Press, 1992. ISBN 1-878822-07-1; ISBN 0-19-855817-1.
• Kozima, Hideo. The Science of the Cold Fusion phenomenon, Elsevier Science, 2006. ISBN 0-08-045110-1.
• Mallove, Eugene. Fire from Ice: Searching for the Truth Behind the Cold Fusion Furor. John Wiley & Sons, Inc., 1991. ISBN 0-471-53139-1.
• Park, Robert L. Voodoo Science: The Road from Foolishness to Fraud. New York: Oxford University Press, 2000. ISBN 0-19-513515-6.
• Storms, Edmund. Science of Low Energy Nuclear Reaction: A Comprehensive Compilation of Evidence and Explanations. World Scientific Publishing Company, 2007 ISBN 9-8127062-0-8.
• Taubes, Gary. Bad Science: The Short Life and Weird Times of Cold Fusion. New York, N.Y. : Random House, 1993. ISBN 0-394-58456-2.

• 1989 Energy Research Advisory Board, "Conclusions and recommendations"
• Recent papers on cold fusion listed on New Energy Times
• Some selected articles on cold fusion
• Britz's cold nuclear fusion bibliography: An extensive overview and review of almost all available publications about cold nuclear fusion.