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Fusion nucléaire par confinement en "bulles"

  1. #1

    Pour information, une dépêche relative à la possibilité d'atteindre la fusion nucléaire dans des bulles via leur cavitation...

    La pression et la température pourraient bien être suffisantes !

    Des articles avaient paru à ce sujet il y a un ou deux ans.

    La revue "La Recherche" y avait d'ailleurs consacré un dossier.

    Je crois me souvenir qu'à l'époque, cette possibilité semblait théorique : les bulles réelles ne pouvant approcher la perfection géométrique requise par les modèles... Il semble pourtant que les expériences actuelles montrent bien la présence de neutrons et de tritium émis par des phénomènes de fusion... et que de nouvelles modélisations les expliquent...

    De là à en tirer une application pratique, il y a un grand pas... Cela est-il possible ?

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    March 2, 2004

    CONTACT: Theresa Bourgeois
    (518) 276-2840

    Researchers Report Bubble Fusion Results Replicated

    Physical Review E publishes paper on fusion experiment conducted with upgraded measurement system

    TROY, N.Y. - Physical Review E has announced the publication of an article by a team of researchers from Rensselaer Polytechnic Institute (RPI), Purdue University, Oak Ridge National Laboratory (ORNL), and the Russian Academy of Science (RAS) stating that they have replicated and extended previous experimental results that indicated the occurrence of nuclear fusion using a novel approach for plasma confinement.

    This approach, called bubble fusion, and the new experimental results are being published in an extensively peer-reviewed article titled "Additional Evidence of Nuclear Emissions During Acoustic Cavitation," which is scheduled to be posted on Physical Review E's Web site and published in its journal this month.

    The research team used a standing ultrasonic wave to help form and then implode the cavitation bubbles of deuterated acetone vapor. The oscillating sound waves caused the bubbles to expand and then violently collapse, creating strong compression shock waves around and inside the bubbles. Moving at about the speed of sound, the internal shock waves impacted at the center of the bubbles causing very high compression and accompanying temperatures of about 100 million Kelvin.

    These new data were taken with an upgraded instrumentation system that allowed data acquisition over a much longer time than was possible in the team's previous bubble fusion experiments. According to the new data, the observed neutron emission was several orders of magnitude greater than background and had extremely high statistical accuracy. Tritium, which also is produced during the fusion reactions, was measured and the amount produced was found to be consistent with the observed neutron production rate.

    Earlier test data, which were reported in Science (Vol. 295, March 2002), indicated that nuclear fusion had occurred, but these data were questioned because they were taken with less precise instrumentation.

    "These extensive new experiments have replicated and extended our earlier results and hopefully answer all of the previous questions surrounding our discovery," said Richard T. Lahey Jr., the Edward E. Hood Professor of Engineering at Rensselaer and the director of the analytical part of the joint research project.

    Other fusion techniques, such as those that use strong magnetic fields or lasers to contain the plasma, cannot easily achieve the necessary compression, Lahey said. In the approach to be published in Physical Review E, spherical compression of the plasma was achieved due to the inertia of the liquid surrounding the imploding bubbles.

    Professor Lahey also explained that, unlike fission reactors, fusion does not produce a significant amount of radioactive waste products or decay heat. Tritium gas, a radioactive by-product of deuterium-deuterium bubble fusion, is actually a part of the fuel, which can be consumed in deuterium-tritium fusion reactions.

    Researchers Rusi Taleyarkhan, Colin West, and Jae-Seon Cho conducted the bubble fusion experiments at ORNL. At Rensselaer and in Russia, Professors Lahey and Robert I. Nigmatulin performed the theoretical analysis of the bubble dynamics and predicted the shock-induced pressures, temperatures, and densities in the imploding vapor bubbles. Robert Block, professor emeritus of nuclear engineering at Rensselaer, helped to design, set up, and calibrate a state-of-the-art neutron and gamma ray detection system for the new experiments.

    Special hydrodynamic shock codes have been developed in both Russia and at Rensselaer to support and interpret the ORNL experiments. These computer codes indicated that the peak gas temperatures and densities in the ORNL experiments were sufficiently high to create fusion reactions. Indeed, the theoretical shock code predictions of deuterium-deuterium (D-D) fusion were consistent with the ORNL data.

    The research team leaders are all well known authorities in the fields of multiphase flow and heat transfer technology and nuclear engineering. Taleyarkhan, a fellow of the American Nuclear Society (ANS) and the program's director, held the position of Distinguished Scientist at ORNL, and is currently the Ardent Bement Jr. Professor of Nuclear Engineering at Purdue University. Lahey is a fellow of both the ANS and the American Society of Mechanical Engineers (ASME), and is a member of the National Academy of Engineering (NAE). Nigmatulin is a visiting scholar at Rensselaer, a member of the Russian Duma, and the president of the Bashkortonstan branch of the Russian Academy of Sciences (RAS). Block is a fellow of the ANS and is the longtime director of the Gaerttner Linear Accelerator (LINAC) Laboratory at Rensselaer. The bubble fusion research program was supported by a grant from the Defense Advanced Research Projects Agency (DARPA).

    About Rensselaer
    Rensselaer Polytechnic Institute, founded in 1824, is the nation's oldest technological university. The school offers degrees in engineering, the sciences, information technology, architecture, management, and the humanities and social sciences. Institute programs serve undergraduates, graduate students, and working professionals around the world. Rensselaer faculty are known for pre-eminence in research conducted in a wide range of research centers that are characterized by strong industry partnerships. The Institute is especially well known for its success in the transfer of technology from the laboratory to the marketplace so that new discoveries and inventions benefit human life, protect the environment, and strengthen economic development.


  2. #2

    Voilà un article complémentaire, qui donne davantage d'informations...



    March 2, 2004

    Evidence bubbles over to support tabletop nuclear fusion device
    WEST LAFAYETTE, Ind. – Researchers are reporting new evidence supporting their earlier discovery of an inexpensive "tabletop" device that uses sound waves to produce nuclear fusion reactions.

    Rusi Taleyarkhan

    The researchers believe the new evidence shows that "sonofusion" generates nuclear reactions by creating tiny bubbles that implode with tremendous force. Nuclear fusion reactors have historically required large, multibillion-dollar machines, but sonofusion devices might be built for a fraction of that cost.

    "What we are doing, in effect, is producing nuclear emissions in a simple desktop apparatus," said Rusi Taleyarkhan, the principal investigator and a professor of nuclear engineering at Purdue University. "That really is the magnitude of the discovery – the ability to use simple mechanical force for the first time in history to initiate conditions comparable to the interior of stars."

    The technology might one day result in a new class of low-cost, compact detectors for security applications that use neutrons to probe the contents of suitcases; devices for research that use neutrons to analyze the molecular structures of materials; machines that cheaply manufacture new synthetic materials and efficiently produce tritium, which is used for numerous applications ranging from medical imaging to watch dials; and a new technique to study various phenomena in cosmology, including the workings of neutron stars and black holes.

    Taleyarkhan led the research team while he was a full-time scientist at the Oak Ridge National Laboratory, and he is now the Arden L. Bement Jr. Professor of Nuclear Engineering at Purdue.

    The new findings are being reported in a paper that will appear this month in the journal Physical Review E, published by the American Physical Society. The paper was written by Taleyarkhan; postdoctoral fellow J.S Cho at Oak Ridge Associated Universities; Colin West, a retired scientist from Oak Ridge; Richard T. Lahey Jr., the Edward E. Hood Professor of Engineering at Rensselaer Polytechnic Institute (RPI); R.C. Nigmatulin, a visiting scholar at RPI and president of the Russian Academy of Sciences' Bashkortonstan branch; and Robert C. Block, active professor emeritus in the School of Engineering at RPI and director of RPI's Gaerttner Linear Accelerator Laboratory.

    The discovery was first reported in March 2002 in the journal Science.

    Since then the researchers have acquired additional funding from the U.S. Defense Advanced Research Projects Agency, purchased more precise instruments and equipment to collect more accurate data, and successfully reproduced and improved upon the original experiment, Taleyarkhan said.

    "A fair amount of very substantial new work was conducted, " Taleyarkhan said. "And also, this time around I made a conscious decision to involve as many individuals as possible – top scientists and physicists from around the world and experts in neutron science – to come to the lab and review our procedures and findings before we even submitted the manuscript to a journal for its own independent peer review."

    The device is a clear glass canister about the height of two coffee mugs stacked on top of one another. Inside the canister is a liquid called deuterated acetone. The acetone contains a form of hydrogen called deuterium, or heavy hydrogen, which contains one proton and one neutron in its nucleus. Normal hydrogen contains only one proton in its nucleus.

    The researchers expose the clear canister of liquid to pulses of neutrons every five milliseconds, or thousandths of a second, causing tiny cavities to form. At the same time, the liquid is bombarded with a specific frequency of ultrasound, which causes the cavities to form into bubbles that are about 60 nanometers – or billionths of a meter – in diameter. The bubbles then expand to a much larger size, about 6,000 microns, or millionths of a meter – large enough to be seen with the unaided eye.

    "The process is analogous to stretching a slingshot from Earth to the nearest star, our sun, thereby building up a huge amount of energy when released," Taleyarkhan said.

    Within nanoseconds these large bubbles contract with tremendous force, returning to roughly their original size, and release flashes of light in a well-known phenomenon known as sonoluminescence. Because the bubbles grow to such a relatively large size before they implode, their contraction causes extreme temperatures and pressures comparable to those found in the interiors of stars. Researches estimate that temperatures inside the imploding bubbles reach 10 million degrees Celsius and pressures comparable to 1,000 million earth atmospheres at sea level.

    At that point, deuterium atoms fuse together, the same way hydrogen atoms fuse in stars, releasing neutrons and energy in the process. The process also releases a type of radiation called gamma rays and a radioactive material called tritium, all of which have been recorded and measured by the team. In future versions of the experiment, the tritium produced might then be used as a fuel to drive energy-producing reactions in which it fuses with deuterium.

    Whereas conventional nuclear fission reactors produce waste products that take thousands of years to decay, the waste products from fusion plants are short-lived, decaying to non-dangerous levels in a decade or two. The desktop experiment is safe because, although the reactions generate extremely high pressures and temperatures, those extreme conditions exist only in small regions of the liquid in the container – within the collapsing bubbles.

    One key to the process is the large difference between the original size of the bubbles and their expanded size. Going from 60 nanometers to 6,000 microns is about 100,000 times larger, compared to the bubbles usually formed in sonoluminescence, which grow only about 10 times larger before they implode.

    "This means you've got about a trillion times more energy potentially available for compression of the bubbles than you do with conventional sonoluminescence," Taleyarkhan said. "When the light flashes are emitted, it's getting extremely hot, and if your liquid has deuterium atoms compared to ordinary hydrogen atoms, the conditions are hot enough to produce nuclear fusion."

    The ultrasound switches on and off about 20,000 times a second as the liquid is being bombarded by neutrons.

    The researchers compared their results using normal acetone and deuterated acetone, showing no evidence of fusion in the former.

    Each five-millisecond pulse of neutrons is followed by a five-millisecond gap, during which time the bubbles implode, release light and emit a surge of about 1 million neutrons per second.

    In the first experiments, with the less sophisticated equipment, the team was only able to collect data during a small portion of the five-millisecond intervals between neutron pulses. The new equipment enabled the researchers to see what was happening over the entire course of the experiment.

    The data clearly show surges in neutrons emitted in precise timing with the light flashes, meaning the neutron emissions are produced by the collapsing bubbles responsible for the flashes of light, Taleyarkhan said.

    "We see neutrons being emitted each time the bubble is imploding with sufficient violence," Taleyarkhan said.

    Fusion of deuterium atoms emits neutrons that fall within a specific energy range of 2.5 mega-electron volts or below, which was the level of energy seen in neutrons produced in the experiment. The production of tritium also can only be attributed to fusion, and it was never observed in any of the control experiments in which normal acetone was used, he said.

    Whereas data from the previous experiment had roughly a one in 100 chance of being attributed to some phenomena other than nuclear fusion, the new, more precise results represent more like a one in a trillion chance of being wrong, Taleyarkhan said.

    "There is only one way to produce tritium – through nuclear processes," he said.

    The results also agree with mathematical theory and modeling.

    Future work will focus on studying ways to scale up the device, which is needed before it could be used in practical applications, and creating portable devices that operate without the need for the expensive equipment now used to bombard the canister with pulses of neutrons.

    "That takes it to the next level because then it's a standalone generator," Taleyarkhan said. "These will be little nuclear reactors by themselves that are producing neutrons and energy."

    Such an advance could lead to the development of extremely accurate portable detectors that use neutrons for a wide variety of applications.

    "If you have a neutron source you can detect virtually anything because neutrons interact with atomic nuclei in such a way that each material shows a clear-cut signature," Taleyarkhan said.

    The technique also might be used to synthesize materials inexpensively.

    "For example, carbon is turned into diamond using extreme heat and temperature over many years," Taleyarkhan said. "You wouldn't have to wait years to convert carbon to diamond. In chemistry, most reactions grow exponentially with temperature. Now we might have a way to synthesize certain chemicals that were otherwise difficult to do economically.

    "Several applications in the field of medicine also appear feasible, such as tumor treatment."

    Before such a system could be used as a new energy source, however, researchers must reach beyond the "break-even" point, in which more energy is released from the reaction than the amount of energy it takes to drive the reaction.

    "We are not yet at break-even," Taleyarkhan said. "That would be the ultimate. I don't know if it will ever happen, but we are hopeful that it will and don't see any clear reason why not. In the future we will attempt to scale up this system and see how far we can go."

    Writer: Emil Venere, (765) 494-4709, venere@purdue.edu

    Sources: Rusi P. Taleyarkhan, (765) 494-0198, rusi@purdue.edu

    James Riordon, (301) 209-3238, riordon@aps.org

    Theresa Bourgeois, RPI director of media relations, (518) 276-2840, bourgt@rpi.edu

    Purdue News Service: (765) 494-2096; purduenews@purdue.edu



    Additional Evidence of nuclear emissions during acoustic cavitation

    R.P. Taleyarkhan1, J.S. Cho2, C.D. West3, R. T. Lahey3, Jr., R.I. Nigmatulin4, and R.C. Block3

    1Purdue University, West Lafayette, Indiana 47907, 2Oak Ridge Associated Universities, Oak Ridge, Tennessee 37830, 3Rensselaer Polytechnic Institute, Troy, New York 12180,
    4Russian Academy of Sciences,
    6 Karl Marx Street, Ufa 450000, Russia

    Time spectra of neutron and sonoluminescence emissions were measured in cavitation experiments with chilled deuterated acetone. Statistically significant neutron and gamma ray emissions were measured with a calibrated liquid-scintillation detector, and sonoluminescence emissions were measured with a photomultiplier tube. The neutron emission energy corresponded to <2.5 MeV and had an emission rate of up to ~4X105 n/s. Measurements of tritium production were also performed and these data implied a neutron emission rate due to D-D fusion which agreed with what was measured. In contrast, control experiments using normal acetone did not result in statistically significant tritium activity, or neutron or gamma ray emissions.

  3. #3

    Voici ce que disait La Recherche sur ce sujet, en juin 2002. Certains vont peut-être devoir réviser leurs premières impressions...

    Comment faire de la lumière avec du son

    Curiosité de laboratoire, la sonoluminescence, production de lumière dans une bulle de gaz comprimée par des ultrasons, a suscité depuis une douzaine d'années les théories les plus exotiques. Des expériences très précises et la conjugaison de connaissances provenant de différents domaines de la physique ont toutefois permis de dissiper la plus grande partie du mystère.
    N°354 - 06/2002 - Dossier - 4271 mots

    Fusion nucléaire et tempête dans un bocal

    Des chercheurs américains pensent être parvenus à provoquer un processus de fusion nucléaire dans un bocal sur une table de laboratoire. Publié par « Science », leur article met en émoi une partie de la communauté des physiciens, dont certains crient au scandale.
    N°354 - 06/2002 - Dossier - 1672 mots

    La « sonofusion » a fait long feu

    La publication de l'article de « Science » a créé un malaise. Les données publiées par les auteurs se contredisent. Renouvelée par d'autres chercheurs dans le même laboratoire, l'expérience n'a rien donné.
    N°354 - 06/2002 - Dossier - 760 mots

  4. #4

    Le New York Times consacre un article à ce sujet...


    La polémique de 2002 refait surface mais la dernière expérience ("peu coûteuse" - 1 million d'euros) semble plus convaincante, même si la mesure de flux de neutrons, cela réserve souvent des surprises parce qu'ils vont dans tous les sens...

    Evidemment, le journaliste parle de production d'énergie...

    Ceci dit, comme dit un commentateur :

    " It's getting to the point where you can't ignore it "

    ( voir notamment www.sciam.com sur Sonofusion, sonoluminescence, etc)

  5. A voir en vidéo sur Futura
  6. #5


    La « sonofusion » a fait long feu

    La publication de l'article de « Science » a créé un malaise. Les données publiées par les auteurs se contredisent. Renouvelée par d'autres chercheurs dans le même laboratoire, l'expérience n'a rien donné.
    N°354 - 06/2002 - Dossier - 760 mots[/quote]

    J'ai entendu cette critique trés souvent pour la fusion froide ou pour la sonofusion, si les essais sont reproductibles j'aurai plus confiance mais actuellement j'ai de trés sérieux doutes

  7. #6

    Le cas de la "sonofusion" pâtit de l'analogie faite avec la "fusion froide".

    Ici, il n'y a aucune remise en cause des lois de la physique et des conditions de température, pression et concentration requises pour atteindre la fusion. De plus, la sonoluminescence en tant que phénomène lumineux est bien établie et connue depuis 70 ans.

    La question est surtout de savoir si la cavitation peut permettre d'atteindre ces conditions dans de telles bulles. Des modèles mathématiques indiquent que cela est possible. Les expériences montreraient la production de neutrons, de tritium et de rayons gamma... de plus, en concordance avec les pics "lumineux".

    On peut se demander s'il n'y a pas eu d'erreurs, par exemple lors de la mesure (toujours difficile) des neutrons.

    Cependant, comme l'expérience est peu coûteuse (moins d'un million d'euros), je suppose qu'elle sera refaite assez facilement par d'autres...

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