Bubble fusion

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Bubble fusion, also known as sonofusion, is the non-technical name for a nuclear fusion reaction hypothesized to occur during a high-pressure version of sonoluminescence, an extreme form of acoustic cavitation. Officially, this reaction is termed acoustic inertial confinement fusion (AICF) (see ICF) since the inertia of the collapsing bubble wall confines the energy, causing an extreme rise in temperature. The high temperatures that sonoluminescence can produce raise the possibility that it might be a means to achieve thermonuclear fusion.[1]



Original experiments

US patent 4,333,796,[2] filed by Hugh Flynn in 1978, appears to be the earliest documented reference to a sonofusion-type reaction.

In the March 8, 2002 issue of the peer-reviewed journal Science, Rusi P. Taleyarkhan and colleagues at the Oak Ridge National Laboratory (ORNL) reported that acoustic cavitation experiments conducted with deuterated acetone (C3D6O) showed measurements of tritium and neutron output that were consistent with the occurrence of fusion. The neutron emission was also reported to be coincident with the sonoluminescence pulse, a key indicator that its source was fusion caused by the sonoluminescence.[3]

Shock wave simulations seem to indicate that the temperatures inside the collapsing bubbles may reach up to 10 megakelvins, i.e. as hot as the center of the Sun. A 2008 study has provided data demonstrating bubble temperatures exceeding 100,000K and a pressure dependence that indicated temperatures above 106K could be expected under sonofusion conditions.[4] Although the apparatus operates in a room temperature environment, this is not cold fusion (as commonly termed in the popular press) because the nuclear reactions would be occurring at the very high temperatures in the core of the imploding bubbles.

The researchers used a pulse of neutrons in order to nucleate ("seed") the tiny bubbles, whereas most previous experiments started with small air bubbles already in the liquid. Using this new method, the team was able to produce stable bubbles that could expand to nearly a millimeter in radius before collapsing. In this way, the researchers stated, they were able to create the conditions necessary to produce very high pressures and temperatures. The sensitivity of the fusion rate to temperature, which is in turn a function of how small the bubbles get when they collapse, in combination with the likely sensitivity of the latter to fine experimental details, may account for the fact that some research workers have reported to see an effect, while others have not.

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