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Table Top Fusion Courtesy of Tiny Bubbles
Erik Baard writes: "The peer-reviewed journal Science is carrying a cover story about the possibility of table top fusion. Not cold fusion, mind you, but the apparatus might look that way to some. Oak Ridge and other labs say they have gotten the fingerprints of fusion (neutron production) from collapsing bubbles in liquid, a process that heats a local area to temperatures as hot as the surface of the sun, and releases photons.
The disputes are already here -- notably from Dr. Robert Park of the American Physical Society and from critical reviewers who say they haven't repeated the neutron production. But the authors say the critics didn't calibrate their equipment correctly. Articles regarding the discovery can be found on
Eureka Alert " CD: Looks legit, but Pons and Fleishman (and the University of Utah for that matter) talked a good game. I suppose I'll belive in tabletop fusion when a generator comes atached to my next laptop. The author of this post also has a longer article up at the Village Voice
I built a single flask apparatus as a senior year thesis as an undergrad...we actually got it to work too. Is it fusion? Now that I'm actually in a plasma physics graduate program I find it very doubtful that what is going on inside those very very small bubbles is actually fusion. I'd love to be able to get back to sono and make a better study of it using some of the plasma knowledge. If it is fusion it has to work along the same lines as ICF..but instead of lasers you have acoustic energy. My feeling when I was working to build the eperiment was that the effect was extremely dependant of the spacial symmetry of the system and the gas content of the liquid...in my case simply water and air. Maybe nanotube technology might provide a way to accurately probe the region near the bubble without perturbing it.
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The big pain of it is the bubbles are so small its extremely hard to make measurenents. Back in 98 when I did my experiment it wasnt even clear in the literature if the light was black body nor what temperature the radiation source was. The water surrounding the bubble has a cut off in the ultra violet and the peak frequency in the emitted light was not observable. I think we found some rather crude theories of shock wave development to would explain some ionization..but i dont think the theories made any estimates of temperatures rivaling that needed for a useful fusion cross section...but of course I didn't know much plasma physics then...it would be interesting to model this in the way ICF target implosion is modeled
If its fusion...I can't imagine this be an extremely useful power source...the bubbles are so small and short lived...if extractable power were produceable I'd imagine the power would heat the sorrounding liquid to the point that the gas dynamics driving the bubble formation would break down well before you could extract any useful heat load from the bulk volume.
Even it its not fusion temperatures in the bubble...its still a very interesting effect....pico sized oven for chemical reactions. Nanotube technology is big now...a pico sized high temp reaction chamber might be very useful for nanotech. My parter and I had a whole shopping list of crude measurements we wanted to try making . Looking for some assymetries in the radiation pattern was the one we really wanted to do.
-jef
Since you asked ... inside a flourescent light tube is argon at a pressure of 3 Torr and mercury at a pressure of 1 Torr (for reference, atmospheric pressure is at about 760 Torr).
... I'll leave it to you to think of household devices which have high energy density.
A electric discharge creates a plasma such that a fraction of the argon and mercury become ionized (it is a very small fraction). As a result, lots of free electrons are running around. Some of these electrons cause excitation of mercury (either directly or indirectly) which after some radiation transport magic is converted to visible light. Some of the electrons cause further ionization which keeps the discharge around.
For ionization and excitation to occur, the electrons have to be at a high temperature. Argon ionizes at 15eV and to have enough electrons that hot you need electron temperatures over 10,000K (typically 40,000K+). The conversion is roughly 1eV to 11,600K.
The catch is that the electron mass is about 70,000 times less than that of argon. To picture what is going on, electrons are ping-pong balls and argon / mercury are bowling balls. Even if you throw a ping-pong ball really really hard, a bowling ball won't notice it.
As a result, the electrons are able to heat up to very high temperatures. Meanwhile, the glass tube at room temperature keeps the Ar/Hg mix cool. Thus, even though the electron temperatures are high, the heat conduction is incredibly low and the tube feels cold to the touch.
Since this site is interested in computers, these types of plasmas are used in almost every step of semiconductor processing. Because the electron energies are so high, exotic high temperature chemisty can be performed without melting your wafer. And because there are charged species, etchant flux can be electrically manipulated (which is why you have microchips which small features nowadays; look up plasma enhanced anisotropic etching).
As for dangerous experiments, I can think of a few but rather than get sued
Kevin
I mostly agree to you, but I just have to be a little pedantic...:)
Regarding the number of neutrons produced by fusion and fission reactions, yes a D-T fusion reaction produces only one neutron while a U or Pu fission produces between about 3, depending on energy. But take into account that a single fusion reaction produces only 17.6 MeV while a single fission produces about 200 MeV. Add to that the fact that a large fraction of the neutrons in a fission reaction are used for inducing further fissions in the material. Remember neutron bombs? Tactical nukes meant to kill the crews of sovient tank hordes, while hopefully leaving the rest of West Germany relatively intact. They had very minimal amount of fission material in them, about 95% of the energy produced was by fusion. The reason was to have a as high as possible neutron flux, and also to minimize fallout. Most strategic warheads deployed today have only about 50% fusion output. The reason is that the casings are made of enriched uranium, the reason being that the Ulam-Teller staged radiation implosion type bomb needs a casing made of high-Z material for refllecting x-rays produced by the primary. So by additionally making the casing of fissionable material (it wont fission by itself, only fission induced by the fusion neutrons) you get better bang-for-weight.
And regarding detonating a fusion bomb without a fission primary, I read some rumors a while ago that the russians reportedly had some chemical explosive called "red mercury" capable of detonating a fusion bomb directly. As it IMHO sounds quite improbable, I'd guess it's just some rumor.