From: terry@asl.dl.nec.com
Subject: Re: Bubbles/Cavitation Fusion in D2 Liquid
Originator: terry@aslss01
Organization: (Speaking only for myself)
Date: Mon, 11 Jan 1993 03:34:52 GMT

Hi folks,

In article <1993Jan8.140538.324@physc1.byu.edu>
jonesse@physc1.byu.edu writes:

> In article <930105122413.20a07695@FNALD.FNAL.GOV>,
> DROEGE@fnald.fnal.gov writes:
>
> | Terry Bollinger has been corresponding with me about his bubble ideas.
> | This has reminded me that Fermilab once had a 15' bubble chamber...
> | 
> | [Tom's interesting idea of how to search for a special class of events
> | in bubble-chamber archives omitted.]
> | 
> | ... The problem is that bubble chamber experiments are very expensive,
> | and no one would likely support running one for such a wild idea.  But
> | if the right old film can be found, it might be worth looking.
>
> Tom, I had the opportunity to work as a graduate student at Fermilab one
> summer, 1976 or thereabouts, with Bob Panvini and Firestone.  We used a
> 200-GeV proton beam impinging on a deuterium-filled bubble chamber, as I
> recall.  So the films from this may have what you are looking for.  Sounds
> fun, but your search may prove expensive.  Should we pursue this?

The idea of such a search sounds interesting, but I'd maintain my stance that
the bubbles in such a warmish (by D2 standards) fluid would be pretty flabby.
Still, you are talking about a _lot_ of bubbles being formed in any one photo,
and a lot of unknowns about the actual intensity of cavitation in such media.


I would in the sake of cost vs. benefits point out that you could also set up
cavitation in a quite smallish tube of (preferably near-freezing) liquid D2
via either decompression (a small piston) or sound (a smaller, faster piston!)
and place it in a good detector.  If your D2's clean I would think you could
get a pretty decently low nominal background count for such a device.

Why bother?  Because extreme cavitation, if it exists, probably has a widely
different set of detailed parameters in D2 than would detection of particles
through bubble formation.  This means that separating generation of how the
cavitation-for-high-intensity from bubble-formation-for-detection would be
more likely to give you a decent event signal, and be easier to control to
boot.

A little beast something like this might be highly portable and not overly
costly to construct:

              Small, tunable   Short tube filled     Small corner reflector
             sonic generator    with test fluid    (intended for 1 node only)
                    |                  |                         |
                    |                  V                         |
                    |                 _____                      |
                    |      ||||||--> |     \                     |
                    +--->  ||||||--> |     *>   <----------------+
                           ||||||--> |_____/  
                                               ("*" = single cavitation node)

The idea above is to tune the frequency of the sonic generator so that the
corner cube reflector will give a _single_ stable node (which will of course
have approximately cubic symmetry.)

The main advantage of such a beast is that you could make it small, portable,
and pretty versatile.  If you which to change the temperature and/or fluid
a sufficiently variable sonic generator should be allow you to re-adjust it
to get back to single-node operation.  You could also use a generator that
is quite a bit wider than the short tube so that you could "chop out" a good
plane wave from an otherwise somewhat iffy waveform (at the cost of losing
simple enclosure of the fluid and making the device quite a bit more complex,
though.)

This is not nearly as powerful or ideal a setup as the spherical ones, but it
has the advantage of versatility and comparative simplicity.  I'd be inclined
to think, for example, that it could stand up a lot better to getting shipped
around from lab to lab than a spherical setup would.  You probably could also
drive a single-node corner-cube pretty ferociously with a good generator and
reflector materials.  Also, don't forget the possibility of making the corner
cubes out of materials that are windows for whatever you want to observe --
e.g., silica for light observations, salt and non-water for UV, etc.

And don't forget etching of corner cubes!  You create corner cubes by etching
a corner-cut from lots of cubic symmetry materials -- e.g., a cross-the-corner
cut in plain old rock salt can be etched with water.  (I'm not sure of the 
quality you'd get, though!)  Or (more complex & dangerous) silicon with HF.
The nice thing about sonic is that just about any rigid material with the
right fluid will give _some_ sonic reflectance, so you've got a lot more
choices than for optical reflectance.  

Etching, by the way, also leads to this "ganged corner reflectors" design:

                     Cavitations
                          |
             Sonic        |    XXXXXXXXX
           Generator    __V  XXXXXXXXXXX
            |||||||--> |  *>XXXXXXXXXXXX
            |||||||--> |  *>XXXXXXXXXXXX 
            |||||||--> |  *>XXXXXXXXXXXX Etched corner-cut cubic crystal
            |||||||--> |  *>XXXXXXXXXXXX (E.g., rock salt for non-H2O work)
            |||||||--> |  *>XXXXXXXXXXXX
            |||||||--> |__*>XXXXXXXXXXXX
                             XXXXXXXXXXX
                               XXXXXXXXX


... in which you are still in single-node operation for each corner reflector,
but you may have many, many such reflectors in the etched crystal.  This one
might be particularly nice for very-short-lamda ultrasound experiments.  If
you try rock salt and non-H2O fluids, it could perhaps also turn out to be a
relatively easy beast to build.


Anyway, perhaps proposed devices of these types might provide a few options
cost-wise for liquid D2 cavitation searches.  Some profs/agencies might even
be willing to fund such a basically off-the-shelf device just on general
research principles, since a well-constructed version should permit orderly
exploration of cavitation curves for a variety of fluids and across a range
of temperatures and sonic intensities.

Also, I suspect (but do not know) that the single-node corner-cube approach
may be novel, and thus could be merit a little research work in its own right.
(That's a warning, too.  If you have any interest in building one of the
above ideas, _please_ note they are just ideas of mine, not validated or even
literature-researched design concepts.)

				Cheers,
				Terry Bollinger