The potential for cavitation to induce nuclear fusion lets physicists think in new directions of energy production
In 2002 the journal „Science“ caused a heated debate among scientists, when it was claimed that thermonuclear fusion was indeed possible in a simple table-top experiment. Until then only nuclear fusion in experimental reactors as big as houses were scientifically accepted. A second publication by the same team in “Physical Review E” (2004) convinced more scientists that there was something to cavitation-induced fusion. Now a confirmation of Bubble Fusion by a second group has been published. The discussion of a potential energy source now takes a new round.
When acetone – better known as nail polish remover – is ultrasonically resonated and irradiated by neutrons, nuclear fusion will occur. That is the claim of the two young physicists Dr. Yiban Xu and Adam Butt from the American Purdue University.
“Cavitation is the phenomenon in which liquid is fractured and a void is formed to form cavities composed of gas and/or vapour”, explains Xu. If the acetone is put into resonance using a piezo-crystal, gas bubbles are formed which subsequently store potential energy in the acoustic field. To ensure that the bubbles get larger than a critical value, the acetone must additionally be bombarded by energetic neutrons. “Once the bubbles implode, that potential energy will convert into kinetic energy, compressing the gas inside the bubble”, says Xu.
It is known that the high pressure and high temperature conditions formed this way do cause light flashes in collapsing bubbles (sonoluminescence). Bubble Fusion now says that these conditions are even extreme enough to cause nuclear fusion when acetone is used where light hydrogen has been replaced by heavy hydrogen (deuterium).
Thermonuclear fusion of two deuterium nuclei is indicated by the production of either a helium-3 nucleus and a neutron or the heaviest hydrogen isotope, tritium, and a proton. In both cases an additional energetic photon is emitted. Xu and Butt claim to measure neutrons and tritium – helium-3 is difficult and a proton impossible to measure in the given environment. “We can be at least 99.994% sure that thermonuclear fusion of deuterium ions has occurred.”
Professor Rusi Taleyarkhan, whose original experiment has been replicated, compliments the two physicists. One would have to owe an important insight to them. Xu: “We found out that when comet-like streamers of bubbles formed the reactions would stop. Their irregular shape diminishes the bubbles’ ability to compress the enclosed gas and subsequently prevents fusion reactions from occurring.”
For the principal editor of the journal „Nuclear Engineering and Design” in which the paper has been published, Bubble Fusion is finally demonstrated. Professor Günther Lohnert, head of the Institute of Nuclear Technology and Energy Systems of the University of Stuttgart, has conducted the review himself and consulted many experts.
For the first time, I would say, in the history of mankind a simple mechanical energy mechanism has shown to be able to produce temperatures considerably in excess of millions of degrees!
Lohnert calls it a „sensation“, that the new experiment is much simpler than the one by Taleyarkhan. Compared to an expensive neutron generator Xu and Butt used a simple plutonium-beryllium-neutron-source. Lohnert believes that Bubble Fusion will now be “the big deal” because physical institutes can pay for it “with petty cash”. He is now trying to arrange for the experiment to be conducted at his institute.
Professor Seth Putterman from the Californian University at Los Angeles thinks, that “the data that [Xu and Butt] presented in the paper is not convincing basically for the same reason as all of Taleyarkhan’s papers.” Putterman demands a timed coincidence between flashes of light due to sonoluminescence and neutron measurements in a time window of a billionth of a second. Taleyarkhan’s group had only shown a correlation to be within a 2 millisecond window.
Indeed it is difficult separating the fusion neutrons from the background which is due to the neutron source. Xu says he and his colleague met such concerns by conducting a control experiment. They carried out an experiment with regular acetone, for which no fusion events are expected. In that experiment they did not measure a neutron difference between cavitation on and off:
We measured a neutron increase of the right energy and a triton increase only for experiments with a deuterated liquid. If the neutrons measured were the same as the seeding neutrons then this should happen for the regular acetone also.
As with the time correlation of light flashes and neutron measurements, Putterman demands a more precise energy diagnosis to verify if the measured neutrons really had the energy that is expected if they are fusion products. In addition, he questions the independence of the researchers.
Taleyarkhan teaches physics at Purdue University, and Xu and Butt work in his laboratory. The two acknowledge that Taleyarkhan helped them designing and setting up the acoustic test cell. As Purdue communicated, the experiments had begun when Taleyarkhan was still employed at Oak Ridge National Laboratory, and had been finished before Xu and Butt joined his lab. “We did our experiment and data analysis independently”, says Xu. For Günther Lohner independence is given by the much simpler experimental setup.
Energy discussion takes a new round
Putterman and Lohnert agree that Bubble Fusion should not become a competitor to Hot Fusion which, following the decision to construct the experimental reactor ITER, is also entering the next round. “Obviously there is a requirement in physics to look at these things more closely and invest money to understand the underlying physics”, Lohnert finds.
Putterman has been trying for at least four years to induce nuclear fusion through cavitation. So far, “the various measurements we’ve carried out including experiments on deuterated cold acetone have yielded no positive results. This doesn’t change my opinion that someday someone will do something very clever to get to bubble fusion.”
Taleyarkhan and co-authors have recently written that Bubble Fusion still has many hurdles to take before it can be considered an energy source. But also Lohnert sees a potential. For this reason the same applied to Bubble Fusion as for Hot Fusion: “If you don’t look at it, you won’t know what it’s good for.”
Putterman thinks that „ people with out-of-the-mainstream ideas should get a small amount of money to carry on with their ideas.” One of those people is Dr. Roger Stringham, a cavitation researcher with experience at public and private research institutions. His company “First Gate Energies” has built a mini-reactor that, according to Stringham, already produces energy – and that since 1989. Although utilizing cavitation, First Gate’s technology is quite different to Bubble Fusion. Stringham last year presented latest results at the “Eleventh International Conference on Condensed Matter Nuclear Science”.
“The Guardian” recently published a letter by Professor Brian Josephson, nobel laureate on the field of condensed matter. The newest Bubble Fusion work “indicates fairly definitively that thermonuclear temperatures can be produced simply, in a table-top experiment, forcing one to take seriously the stronger claims of Stringham et al.” Josephson closed his letter with a question: "Dare one hope that some of ITER's budget might be diverted to possibilities such as these?"
Correction The article says that time correlation of light flashes and neutron measurements was only shown by Taleyarkhan et al. to be within a 2 millisecond time window. This refers to the overall time span in which correlations occurred (Phys. Rev. E., 2004, fig.7). Earlier Taleyarkhan et al. had already shown coincidences to be within a time window of roughly 10 nanoseconds (Science, 2002, fig.5a).