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Return of Sonofusion
Jamais Cascio, 24 May 05

In Sonofusion (2004), we talked about Purdue physicists demonstrating thermonuclear fusion takes place in tiny bubbles in liquids hit by a pulse of neutrons and ongoing acoustic oscillation (i.e., sound); In Son of Sonofusion (2005), we talked about researchers at the University of Illinois Urbana-Champaign confirming aspects of the research, including the extremely high temperatures found in the collapsing bubbles (we're talking much hotter than the surface of the Sun). Now sonofusion returns, hotter and more powerful than ever...

The Purdue-led team -- Richard Lahey Jr., Rusi Taleyarkhan and Robert Nigmatulin -- have an article in the current IEEE Spectrum Online, the newsletter of the Institute of Electrical and Electronics Engineers, a well-regarded and very serious group of technical professionals. In "Bubble Power," Lahey et al go into substantial detail about how they figured out sonofusion (now referred to as "acoustic inertial confinement fusion") and the current state of their research. The summary version: this looks like it could be surprisingly, startlingly real, with pretty astounding potential.

IEEE Spectrum is aimed at an audience comfortable with technical and scientific jargon, but I found the piece gave an extremely readable account of just how the sonofusion technique works. In short, a flask filled with a liquid -- in the original experiments, acetone -- in which 99.9 of the hydrogen are of the more-readily-fused "deuterium" isotope is hooked up to a piezoelectric crystal used to produce acoustic waves in the liquid. At a certain frequency of oscillation, the liquid creates a standing wave which concentrates sound energy. A 6 microsecond burst of neutrons into the liquid knocks some of the molecules around, which in turn creates a small number (~1000) of tiny bubbles with a radius of a few tens of nanometers. But the pulsing oscillation is rapidly changing the pressure in the liquid, and during the low pressure part of the cycle, the bubbles swell by 100,000 times; when the pressure goes back up, the bubbles collapse with such force and energy that the small amount of "deuterated acetone vapor" undergoes thermonuclear fusion, producing temperatures (for a split second, in a tiny space) of 100 million °C. (A graphic of how all of this works can be found here -- PDF.)

Sounds impressive. But the amount of actual energy produced by the split second, tiny fusion events is actually rather small. And they aren't sustained without an ongoing neutron flow. Neither of these are insurmountable problems (and the Lahey, et al, piece in IEEE Spectrum includes some intriguing suggestions of just how they will be overcome), but they are significant barriers. Additional challenges arise from the difficulty of getting sonofusion to work. Although Lahey, et al, claim to have done so repeatedly (and have proven their case sufficiently to pass extra-heavy peer-review criticism prior to the 2004 article), no other lab has managed to duplicate the Purdue results completely. Plenty are trying, both in academia and in commercial ventures, but until sonofusion can be regularly triggered in the lab, it will carry a bit of "cold fusion" flavor for some observers.

If acoustic inertial containment fusion doesn't actually work, then it will go on the pile of failed efforts and will soon be forgotten. If it does work, but can't (for some reason) scale up to usability, it would still be a useful tool for fusion research -- perhaps even a good stepping stone to figuring out large scale "traditional" fusion. But if it works, and the technical challenges to getting it to produce usable amounts of energy are overcome, then it would be worldchanging news.

As Lahey, et al, put it:

...the Holy Grail of all fusion research is the development of a new, safe, environmentally friendly way to produce electrical energy. Fusion produces no greenhouse gases and, unlike conventional nuclear fission reactors, it produces no noxious radioactive wastes that last for thousands of years. With the steady growth of world population and with economic progress in developing countries, average electricity consumption per person will increase significantly. Therefore, seeking new sources of energy isn't just important, it is necessary. Much more research is required before it is clear whether sonofusion can become a new energy source. But then there is just one way we can find out—we will continue making bubbles.

Fusion is appealing in principle because, as mentioned above, it produces no substantive radioactive wastes (years of neutron flux eventually make the containment vessel mildly radioactive, but nowhere near as dangerous as plutonium) and there's no way to turn the fusion reactor into a weapon. There's no radioactive fuel to leak, and pulling the plug just makes it drop below fusion temperatures, ending the reaction. There's a philosophical appeal, as well: fusion is the primal energy of the universe, the ultimate source of all other energy (solar power is just using the results of stellar fusion, and wind power is the result of solar energy heating the atmosphere).

Despite the ongoing developments in wind, solar, tidal and biofuels, it would be good to add fusion -- especially in a form that doesn't require massive, multi-story reactors -- to our toolkit of power sources. Every method has its drawbacks, and the greater diversity of energy options we have, the better we'll be able to handle unexpected demands and problems. Sonofusion's biggest drawback, for now at least, is that it's entirely unproven.

If sonofusion works -- and we're probably still another couple of years from having solid confirmation -- it will take a decade or two at least before we could see any real world applications from it. It's not going to save us from having to do the hard work of moving away from fossil fuels. But another decade or two would mean it would be starting to come online in the early part of the 2020s, just when the conversion from gasoline and coal will start to really hit high gear -- an ideal moment, then, for another clean source of power to step onto the stage.

By 2050, we could be living in a world powered by wind, the Sun, and stars in a jar.

(Thanks to Eric Boyd for pointing me to the articles!)

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Comments

I'm waiting for duplication of the results by teams independent of Taleyarkhan. There has been some depluplication some of Taleyarkhan's but not enough to make me believe that sonofusion is a reality, let alone a potential energy source.

But let's assume sonofusion is fact. There still is the problem of scaling it up to give everyone the star-in-a-jar desktop powerplant so long dreamed of in science fiction.

Many of the short stories I've read that posited such wonders often immediately followed with depictions of global depression and enormous economic disruption as entire industries became irrelevent. This last probably won't happen considering all the hurdles in the way, governments and industry will have plenty of warning.

And of course, I entirely agree that energy diversity is best. Conservation and efficiency being the key things to focus on.


Posted by: Mr. Farlops on 25 May 05

It's fascinating stuff!


Posted by: Daniel Johnston on 25 May 05

I would have thought Taleyarkan had been quite thoroughly depluplicated by failed attempts at independent replication, e.g. http://news.bbc.co.uk/1/hi/sci/tech/4270297.stm,
e. earlier g. Saltmarsh and Shapiro.

--- Graham Cowan, former hydrogen fan
boron: how individual mobility gains nuclear cachet


Posted by: G. R. L.Cowan on 26 May 05

Neat stuff, sure beats the old inertial confinement method of pointing a whole bunch of lasers at a point and hoping for the best...

I like the idea of keeping diverse energy production tools on hand, fitting the best technology to the best application.

There's one thing about fusion that has been bugging me lately though. It is certainly a clean, abundant, (potentially) cheap form of energy, but is it sustainable?

All energy "produced" in the form of mechanical or electrical energy ultimately ends up as heat. In order to sustain a given temperature, any discrete object, like the earth, needs to dissipate any new heat back out into its surroundings (space). Up until recently, all of the energy the earth had to dissipate came from the sun. If you put an addtional sun-like object on the surface of the planet in the form of a fusion generator (especially at the scales traditional fusion generators are designed for) how can you really prevent global warming? No need to capture added heat with greenhouse gasses, just produce it outright.

How long till we need a planetary heat sink? How much more energy will that take to run? (see the downward spiral? Granted, this probably only applies to large-scale fusion projects.)

The way things are going with fossil fuels, fusion may be a necessary stepping stone, but can anyone elaborate on how it is ultimately sustainable unless you are talking about some self-contained outpost in space?


Posted by: N. Eng on 26 May 05

As I understand it, the scale of the heat produced by these generators would be a tiny fraction of that hitting the Earth from the Sun every day, and wouldn't add considerably to overall planetary heat. Similarly, global warming is happening due to solar heat being trapped, not the heat resulting from inefficient engines and generators of the present.


Posted by: Jamais Cascio on 26 May 05



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