Tiny Bubbles Implode With the Heat of a Star( possible fusion )

When the force of sound waves implode tiny bubbles within a liquid at room temperature, the surface of the bubble can reach temperatures at least 25,000 degrees Fahrenheit, more than twice as hot as the surface of the sun, scientists reported this month.

The scientists, at the University of Illinois, did not speculate just how hot the bubble became, but said they had managed to create a state of matter called plasma inside the bubble. In it, some of the electrons have been stripped off the atoms.

"This is the first definitive proof of the existence of a plasma" during this kind of bubble implosion, said one of the scientists, Dr. Kenneth S. Suslick, a professor of chemistry at Illinois.

Their finding supports the intriguing notion that it may be possible to compress these bubbles so violently that vapor molecules in them are heated to multimillion-degree temperatures.

The phenomenon of imploding bubbles, called sonoluminescence because it emits a flash of light as the bubble collapses, has been increasingly studied since it was discovered 15 years ago.

In 2002, scientists performing an experiment at Oak Ridge National Laboratory in Tennessee even reported that they had used the technique to fuse hydrogen atoms into helium - the process that powers the sun. That experiment did not measure the bubble temperatures, but detected byproducts of fusion.

The Oak Ridge scientists said each burst produced only a smidgen of energy, but they speculated that it could develop into a practical power source.

Most other scientists remain skeptical of that claim, because the experiment has not yet been reproduced elsewhere, but the science increasingly appears at least plausible.

"I'm becoming skeptical about my earlier skepticism," said Dr. Lawrence A. Crum, a professor of electrical engineering at the University of Washington. But he added, "I won't say it's likely."

The latest results, reported in the journal Nature, did not offer signs of fusion. Rather Dr. Suslick and David J. Flannigan, a graduate student, provided tantalizing hints that these bubbles could reach temperatures high enough for fusion.

In the experiment, they created a single bubble in a jar of sulfuric acid and observed as sound waves above 18,000 cycles per second resonated on the liquid, causing the bubble to grow and collapse over and over.

Sulfuric acid has a lower vapor pressure than water, which had been used in most previous sonoluminescence experiments, allowing the bubble to collapse more quickly and produce flashes 3,000 times as bright as those seen in earlier sonoluminescence experiments.

The sulfuric acid contained trace amounts of argon gas, which emitted specific colors of light as the bubble collapsed, allowing the researchers to determine the temperature.

Dr. Suslick and Mr. Flannigan also detected colors from atoms that had had some of their electrons stripped away, forming a plasma, which would be a prerequisite for fusion to occur.

To form some of the charged atoms seen in the Illinois experiment, he said, at least some electrons flying out from the center of the bubble would have had an effective temperature greater than 250,000 degrees.

Dr. Suslick agreed that some of the electrons did have that much energy, but he said that the overall temperature - the average energy of all the electrons - might not have been that high.

His findings, he added, do not prove nor disprove the controversial Oak Ridge experiment, which employed a very different setup. For example, the Oak Ridge researchers used acetone, which has a higher vapor pressure, but were also able to generate much stronger sound waves.

"Will it lead to desktop fusion generators?" Dr. Suslick said. "I can't answer that yea or nay right now."

The only known attempt to reproduce the Oak Ridge experiment was by Dr. Seth Putterman of the University of California, Los Angeles, whose the work was financed by an unusual source, the BBC. For an episode of its "Horizon" science series that focused on the Oak Ridge experiment, the BBC gave Dr. Putterman $70,000 to try to replicate it.

"I'm desperate for money, and here's a chance to infuse my laboratory with overhead-free money," Dr. Putterman said. "We had fun."

But his experiment saw no sign of the fusion-generated neutrons that had been reported.

Dr. Rusi P. Taleyarkhan, the head of the Oak Ridge experiment, said there were notable differences between his set-up, which cost close to $1 million, and the one put together by Dr. Putterman. "Sometimes you get what you pay for," said Dr. Taleyarkhan, now a professor of nuclear engineering at Purdue.

Dr. Putterman said the Defense Department was planning to spend $800,000 - $350,000 for his group at U.C.L.A., $350,000 for Dr. Taleyarkhan and $100,000 for Dr. Suslick's group at Illinois - for a full-fledged effort to repeat the original experiment.

Dr. Taleyarkhan said, however, that he not yet agreed to participate. "At one point, I did consider going forward," he said, "and we might still accept."

More info from a different article

Astronomers can't poke a thermometer in the sun's mouth, or elsewhere, to take its temperature, so they use light.
That is, they extrapolate the temperature from the relative intensity of the lines in the spectrum of light from the sun and other stars, essentially the variations in the colors or wavelengths of light they give off.
University of Illinois researchers have applied a similar technique to tiny gas bubbles in liquid that are formed, grown, isolated and collapsed by ultrasound and found something hot. Real hot.
The temperature inside a single collapsing bubble is more than 26,000 degrees – about three times hotter than the surface of the sun.
And that's just at the outer regions of the bubble. It's probably even hotter at the center and a violent shock wave likely accompanies the bubble's collapse as well, UI Professor Ken Suslick said recently.
No need to avoid the UI Chemical & Life Sciences Lab, where Suslick and doctoral student David Flannigan do their work, however. The hot spot and shock wave are on the same very small scale as the bubbles with which they work. The minireaction also is contained by being centered in and surrounded by a flask of otherwise cold liquid, Suslick said.
The light emitted with the high heat inside is another matter. It's bright enough to see in the hallway outside the darkroom where Flannigan does the experiments, even with the room lights turned on, Flannigan said.
"It hurts to look at it sometimes," he said.
Bright enough to measure the temperature of the reaction, which had never been done with a single-bubble collapse before. Suslick and Flannigan reported their results in the journal Nature this month. The National Science Foundation and the Defense Advanced Research Projects Agency have supported the work.
In addition to being a first, the study has attracted attention because some scientists at Oak Ridge National Laboratory have previously reported evidence of nuclear fusion in such sonoluminescence, or "sound-into-light," bubble-collapsing experiments.
The Oak Ridge claim, released in 2002, was widely disputed, and the UI researchers reported no such result in nature.
Suslick, a UI chemistry professor, said earlier attempts to measure the temperature of a single-bubble collapse failed largely because they employed water.
Water has a high vapor pressure, which in this case means a lot of water molecules get inside a bubble and absorb much of the compressive force, resulting in the spectrum of light emitted being poorly delineated.
Suslick's lab had been testing substitute liquids and liked the looks of sulfuric acid because it has a low vapor pressure and emits a light pattern nearly 3,000 times as brilliant as water.
Flannigan first uses ultrasound to vibrate the flask of liquid and create a standing wave that pushes a single bubble to the center. Suslick likened it to throwing a rock in a pond, only with the ripples circling inward instead of outward.
Once the bubble is centered, the UI researchers turn up the ultrasound, the force of which collapses it.
"When you compress a gas, you get heating," Suslick said. "Anybody who's pumped up a bicycle tire knows that."
As the bubble collapses, the reaction actually yields plasma – charged gas and the stuff of which stars are made – and the UI researchers use a spectrophotometer to measure the light emitted in the process. It's a device similar to those used by astronomers, in conjunction with telescopes, to measure light from distant stars, Suslick said.
In our everyday lives, the light emitted by plasmas is the basis of fluorescent lighting and plasma TV screens, among other things.
Likewise, the ultrasound the researchers employ is the same tool used for medical procedures, but at a different frequency and intensity.
The use of ultrasound to collapse bubbles – called "acoustic cavitation" – by Suslick and colleagues is more than a hot academic exercise.
They can use the high-energy, high-temperature reactions not only to produce light but also to produce unusual chemical materials and nanoscale structures. A nanometer is a billionth of a meter, about 200,000 times smaller than the diameter of a human hair.
For example, they've already created hollow nanospheres of a material, molybdenum-disulfide, which appears to be a superior catalyst for removing polluting sulfur compounds from gasoline, and box-shaped crystals with spherical voids inside. Such tiny vessels might be useful, say, for delivering drugs to a specific place in the body.
"There are all kinds of chemical applications for ultrasound," Suslick said. "Every bubble is (potentially) a separate nanoreactor."

http://www.news-gazette.com/localnews/story.cfm?Number=17856

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