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- Newsgroups: sci.physics.fusion
- Path: sparky!uunet!gatech!concert!uvaarpa!murdoch!kelvin.seas.Virginia.EDU!crb7q
- From: crb7q@kelvin.seas.Virginia.EDU (Cameron Randale Bass)
- Subject: Re: Sonoluminescence - certain knowledge?
- Message-ID: <1993Jan6.191134.19959@murdoch.acc.Virginia.EDU>
- Sender: usenet@murdoch.acc.Virginia.EDU
- Organization: University of Virginia
- References: <00966330.AB98DB60.10309@dancer.nscl.msu.edu>
- Date: Wed, 6 Jan 1993 19:11:34 GMT
- Lines: 83
-
- In article <00966330.AB98DB60.10309@dancer.nscl.msu.edu> blue@nscl01.nscl.msu.edu writes:
- >Could someone set my mind at ease by making a clear statement as to
- >what is know about sonoluminescence, ultracavitation, and related
- >topics as opposed to conjecture based on doubtful interpretations of
- >a very limited data set?
-
- The dataset is not as limited as it sounds, and the recent results
- are a) consistent with earlier results, b) plausable on theoretical
- grounds, and c) apparently well done.
-
- >My understanding of cavitation and bubble formation is that it can
- >involve a very small move away from equilibrium conditions. All that
- >is required is that the local pressure in the liquid fall below the
- >vapour pressure. I would assume that the bubble fills with vapour
- >on a time scale close to that required for collapse so I don't
- >understand why there is any talk about collapse into a "void".
-
- Yes. Void is used by fluid dynamicists to talk about a
- space filled with vapour. We shouldn't be talking about a vacuum.
-
- >Now as to sonoluminescence, I have the feeling that the conjectures
- >have run somewhat ahead of the facts in a chain of reasoning that goes
- >something like the following: The emission of visible light from
- >a gas implies high excitation energies such as would result from
- >temperatures of many tens of kilovolts or higher so we can conclude
- >the sonoluminescence indicates conditions similar to high-temperature
- >plasmas are being produced in the bubbles. It is but one small jump
- >from there to say that this might be a path to fusion. It seems to
- >me, however, that this chain of reasoning has several weak links.
- >Suppose I suggest as an alternative point of view the notion that
- >the observed photons are not produced in the volume of the bubble at
- >all, but are instead coming from the boundary layer of the bubble?
- >What does the experimental data tell us in that regard?
-
- No, it is not a small jump. There are clearly shock phenomena
- that involve ionization and dissociation, that upon species
- recombination can emit light. To then postulate nuclear excitation
- from this is not a small leap at all, and the weak links are
- basically nonexistent links.
-
- As far as the photons, they appear to be locallized at the
- center of the bubble in 'stable cavitation'. This would make sense
- if there were a strong shock-dissociation-recombination chain
- of events inside the vapour bubble.
-
- As far as the spectra go, they are an attempt to fit the
- observed spectral energy density of the flashes to a blackbody spectrum
- (e.g. PRL 69:1182 (1992)). I think they have doubtful physical
- significance from this perspective.
-
- >Why would I think that the light emission is a surface effect? Basically
- >because it is something easy to mimmick in the privacy of your own home,
- >and it can even be done in your kitchen. Just unroll some plastic wrap
- >in a dark kitchen. The layers of plastic film stick together because
- >the material is a polar dielectric. When you pull the layers apart the
- >surfaces are left with unpaired charges in a nonuniform distribution
- >that is then equilibrated by surface discharges. When I form a bubble
- >in a polar dielectric liquid might I not produce the same effect?
-
- This is related to one of the old theories before it became apparent
- it was coming from the middle of the bubble. A number of others
- are discussed in Ronald Young's book 'Cavitation' (McGraw Hill (1989)).
-
- >I have one more question relating of fractofusion, bubbles, and
- >non-equilibrium. Suppose by hook or crook I do produce a transient
- >electric field in the presence of some deuterons and some electrons.
- >What keeps the electrons sitting still while the deuterons accelerate
- >to velocities high enough to induce fusion? I have always be taught
- >that a mass ratio of roughly 4000:1 would leave the deuterons sitting
- >still while the electrons rushed off to cancel the field. Of course
- >that is old fashioned theory.
-
- Absolutely. Any prospective theory of such a process must explain
- a) exactly how one overcomes the repulsion, and b) why other things
- to not interfere. One other minor point, it should probably also
- agree with experiments.
-
- dale bass
-
- --
- C. R. Bass crb7q@virginia.edu
- Department of Wildebeest
- Transvaal (804) 924-7926
-