From: crb7q@kelvin.seas.Virginia.EDU (Cameron Randale Bass)
Subject: Re: Sonoluminescence - certain knowledge?
Organization: University of Virginia
Date: Wed, 6 Jan 1993 19:11:34 GMT

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
Newsgroups: sci.physics.fusion