NetNews Usenet Archive 1993 #1/NN_1993_1.iso/spool/sci/physics/fusion/3192

Text File | 1993-01-07 | 15.2 KB | 304 lines

Newsgroups: sci.physics.fusion
Path: sparky!uunet!haven.umd.edu!darwin.sura.net!gatech!concert!uvaarpa!murdoch!kelvin.seas.Virginia.EDU!crb7q
From: [e-mail] (Cameron Randale Bass)
Subject: Re: Responses to Dale Bass
Message-ID: <[e-mail]>
Sender: [e-mail]
Organization: University of Virginia
References: <[e-mail]> <[e-mail]> <[e-mail]>
Date: Thu, 7 Jan 1993 18:23:37 GMT
Lines: 292

In article <[e-mail]> [e-mail] writes:
>Hi folks,
>
>In article <[e-mail]>
>[e-mail] (Cameron Randale Bass) writes:
>
>> [Terry Bollinger writes:]
>>
>> | Can anyone out there show one way or the other whether this wedge-out
>> | idea is either bogus or has merit?
>> ...
>>
>> 1) in stable cavitation in acoustical fields, the sonoluminescence occurs
>> shortly after the bubble reaches maximum radius (i.e. just as the bubble
>> starts its inward cycle.  Keep in mind that in stable sonoluminescence,
>> the bubble itself does not completely collapse.).  This implies that the
>> sonoluminescence is mediated by a strong shock in the vapor itself (See
>> Barber and Putterman PRL: 69:3839 (1992) among others),
>
>In the UC draft I did assume vapor or gas in most bubbles, but (by choice)
>emphasized keeping the vapor level low.  I dropped the use of "shock
>wave" from my first outline for that same reason.  I was interested mainly
>in _very_ thin shock wave media, not the conventional thick stuff.  (In
>retrospect I wish I had left the "shock" terminology in there.)

     Why the 'thick' vs. 'thin' stuff?  A shock is a shock.  They are
     usually pretty thin.  A vacuum bubble collapsing does not necessarily
     create a shock, it is also not necessarily energetic.

>> Putting aside the thought that it probably has limited physical meaning,
>> at that point there are very good electrostatic reasons for the character
>> of the interaction to change somewhat drastically.
>
>Sorry, I don't get it.  If the plasma is created through thermal methods and
>is not being subjected to intense currents or magnetic fields, my assumption
>was (and is) that it will be subject to the same general dynamic behavior as
>any very hot gas.  Are you implying that you think a strong field or current
>will be present?  If so, why?  It would seem like an unnecessary assumption
>without a lot more evidence for the presence of such phenomena in the center.

      You have a small region of very hot gas inside a large region
      of very cold gas.  In fluids, all interactions occur via
      electromagnetic means.  How does one avoid large currents or
      large fields while doing such a thing (i.e. fusion within a bubble)?
      My contention is that the bubble avoids such large fields by not doing
      precisely the thing you want it to.  There is good experimental
      reason to believe that fusion does not occur significantly
      in shocks (you'd have technicians everywhere dying of radiation
      poisoning), so the assumption that shocks can concentrate energy
      in a manner sufficient to produce fusion seems to be the unnecessary
      one.

      The only way I know to do such things is to do things the way
      ordinary hot fusion people do things.  Keep in mind we are still
      discussing processes that occur at much larger scales and much lower
      energies than are necessary for fusion.
>
>> I would also point out that the concept of ordinary fluid dynamic surface
>> tension breaks down well before that point (to put it mildly).
>
>From conversations with you offline, I gather that you were originally under
>the impression that I was trying to whack the fluid surface all the way into
>the center of the void.
>
>I most decidely proposed no such thing in UC, and I explicitly described the
>"wedge-out" as a proposed _gaseous_ effect.
>
>Moreover, in UC I described the wedge-out in the context of a very fast,
>inwardly moving gaseous front that has a very sharp transtion from high
>pressure to (hopefully) low void pressure on its leading edge...
>
>You'll pardon my lack of using standard terminology at times, but I believe
>that such a thing is called a "shock wave," is it not?
>

     If it is to be a shock wave, you will get no fusion under ordinary
     circumstances.  The way to do this in reality is exactly the way
     the US and Russian militaries do it, nuclear driving pressure.

     This is the problem with theories that are not quantified.  I think
     you'll find that the driving pressure required to induce fusion is
     substantial.

>> 3) If you seriously want to present a model, the burden of proof is on you
>> to describe such things as
>>
>> a) why your process does not violate the second law,
>
>Hmm?  Since when does the second law prevent _local_ increases in temperature
>and pressure as long as they don't reduce entropy for the system as a whole?

     This is not the way a shock wave works,  you are requiring a coherent
     wedge eject itself from the fluid under solely thermal and dynamical
     influences, and you are requiring it to continue to cascade.  Unless
     you can show it does not violate the second law, I have a hunch it
     does.  The way to show it is to consider the entropy of the fluid
     before formation of the wedge and after.  It is probably not all that
     difficult a calculation.

>Whatever sonoluminscence is, it's clearly expending a lot of energy in the
>whole bubble to produce an increase in energy in a _much smaller_ central
>region.  So what?  Multi-stage rockets behave quite similarly when they
>accelerate a payload, but they certainly don't violate the second law.
>

     Multistaged rockets are well-organized, fluids are not.  Don't
     get me wrong, shocks can concentrate energy, but
     they are fairly well understood as far as fusion goes.

>Speaking of such things, David Cyganski sent me a very nice (and easy-to-do)
>example of how mechanical bouncing around (literally!) can result in the
>energy of one object being transferred largely or entirely into another one:
>
>Take two elastic balls, one of which is about 1/3 the weight as the other.
>Carefully drop them so that the light ball rest exactly on top of the heavy
>ball as they fall.
>
>If the weights are about right, then when they both hit the ground the heavier
>ball will transfer _all_ of its kinetic energy to the lighter ball, which will
>then rebound much higher than the height from which it was dropped.
>
>Does the ball violate the second law?  No, of course not.  Nor does the idea
>that the collapse of a highly symmetrical void could produce a brief, highly
>energetic central region.  A close cavitation system with a self-contained
>energy source increases in entropy quite nicely over time, no matter how
>hot certain individual events within that system may or may not become.

     Absolutely, if you are allowed to micromanage the fluid and it behaved
     like steel balls, you'd be set.  However, it does unfortunate things like
     sit in a fairly high entropy state and ionize and have a non-billiard
     ball kind of behavior when one gets it hot.  It also does not have the
     tendency to form wedges.  You can do almost anything if allowed to
     put the fluid molecules in an arbitrary state of energy or entropy.

     It would be easier to simply assume that all the ionized deuterons
     had some massive energy and were all heading towards a single point.
     You'd get substantial fusion there.

>> c) why diffusion and damping do not significantly operate,
>
>The stupid answer is "because it's spherical and it's collapsing inward."
>Things are getting damped, alright, but most of what is getting damped is
>also getting "left behind" as the wave front moves inward.

     It isn't spherical, you've given it structure.  If it is spherical
     it is a shock and works via ordinary shock mechanics.

>> d) how one applies a fluid continuum approach to a putatively ionized gas,
>
>Again, I'm ignorant.  Is neutal plasma "sticky," or what?  Can you elaborate?

     All fluids are 'sticky' or 'repulsive' to one degree or another,
     however, the point is that the electrons will react to, say, strong
     'mechanical' forcing much faster than the ionized deuterons you
     hope to force.  One must always keep in mind that 'mechanical' forcing
     is electromagnetic forcing for all ordinary fluids and plasmas.
     You are applying a fluid continuum model down to scales
     where it clearly does not apply at low energies
     (low is defined as energies that are not equal to or greater than
     those found in your average tokamak.  For mercury, low is defined as
     energies not equal to or greater than energies found in your average
     supernova).

>> e) how one can get a further 11 order of magnitude concentration of energy
>> beyond the concentration probably caused by an ionizing shock, especially
>> considering that at indicated spectral temperature, electromagnetic
>> interactions will dominate long before fusion energies are reached,
>
>Hey, I said measureable _low level_ fusion.  I don't recall the curves
>that used to be discussed in this group, but it seems to me that a real
>kinetic energy of 100,000 K might _already_ be high enough for some very
>low level increases in, say, T-T that could be detectable.  (Anyone game?)

     As I attempted to say earlier, the 100,000 K is taken from an
     assumption of black-body radiation applied to the light spectra
     from the sonoluminescing region.

     Even if it is not simply the representation of a huge peak
     of a single recombination process, it does not seem a) physically
     realistic to apply a equilibrium description to a clearly nonequilibrium
     process, b) physically plausible.

     However, assuming we have an equilibrium process, as far as 100,000K
     being sufficient to cause T-T fusion, I'd bet that the fusion
     probability is very very very low.  In any case, you're back to hot
     fusion caused by shock waves.  This is not a viable process at
     low energies.

>On the other hand, I honestly _don't_ feel that the concentration curve has
>been anywhere near exhausted yet, because I don't think there is a full
>understanding of what is going on for some ranges of the effect -- such as
>for exceptionally low void pressures.

      What's below zero?  I don't think it suits your purpose to put the fluid
      in tension.  The important thing is the pressure differential.

>I say that if you thin the medium through which the shock wave travels, you
>will get an intensification.  I also note that the slanting of SL spectra
>towards the UV when the water is cooled are nicely compatible with that
>prediction.  Have any of the other seven or so models predicted that?

      You also lower the drive pressure, there is also a limiting value
      for the mean velocity which is related to the temperature, which
      is fairly small at ordinary temperatures (fairly small in relation
      to energies required for fusion, and ordinary includes 100000K).

      Shock waves are fairly well-understood, try Courant and Friedrichs
      "Supersonic Flow and Shock waves".
>
>> f) why it seems to be somewhat at variance with current indications of the
>> mechanism of stable sonoluminescence.
>
>I did not take shock waves composed of void media into account, yes.  I only
>mentioned elastic compression and the idea that more void vapor should reduce
>the overall intensity of the event.
>
>But I don't think we're talking about a major mismatch here.  Indeed, there
>shoud be a continuum of effects between whacking a thick void gas and sending
>off a shock that way, versus cavitations in which the void surface itself is
>vaporizes and begins "filling in" a sparsely filled void with a particularly
>vicious (and dense) shock wave.

     How does one vaporize a vapor?  In any case, there is a kinetic limit
     on the velocity of the molecules in a very rarefied situation at ordinary
     temperatures.  The limit is somewhat below fusion energies, to put
     it mildly.

     There is certainly a continuum of shock waves.  I don't believe
     any of the ones at ordinary energies have been found to cause fusion.

>> If so, it appears to be of limited value in fusion studies unless you can
>> explain why a partially ionized gas can further concentrate energy.
>
>How about the other way around:  Why can it _not_ for if the plasma is
>electrically neutral and no large fields are present?

     Large fields *are* present whenever you get two positive ions
     very very close together.

>> Our good friends in the hot fusion business can probably explain better
>> than I how difficult that is.
>
>Sounds good.  Could some kind soul explain the added instabilities that
>make neutral (?) plasmas behave differently from high-temp gases?

     They are not added instabilities necessarily.  It is just that
     you wish to fuse the component ions.  To do so you must give them
     enough energy to get them close together, the charges on the
     ions tend to prevent a) giving them enough energy, and b) getting
     them close together.
>>
>> So something that is doubly ionized is harder to get close together than
>> something that is 80x ionized?  Keep in mind, at hot fusion energies your
>> original fluid is gone.  All that remains is that nucleus and all its
>> charges.
>
>Again, you seem to be assuming that the plasma as a whole has lost the
>neutralizing effect of its electrons.  I have no knowledge of any physical
>basis for that kind of assumption.  Also, most plasmas do _not_ totally
>ionize all elecrons, especially from heavy metals.  I don't understand
>your point in suggesting such extreme ionization, which almost certainly
>could not occur even in a tokamok or other comparable plasma devices, let
>alone in whatever (if anything) is going on in cavitation.

     Providing you've overcome the obvious, there *are* no electrons down
     where you're going.  At some point the two 'fusing' bodies are
     well within each other's wells, and they don't like to be there.
     You have this problem if you ionize them, if you don't ionize them,
     if you partially ionize them.  Fusion is far down below the inner shell,
     where electrons dare not tread.  This is one of reasons hot fusion people
     use hydrogen isotopes instead of heavier elements.

>
>P.S. -- I will be re-issuing a discussion of the wedge-out with a new emphasis
>        on development of flow-cells (formerly called wedges) at the margin
>        of a converging "shock front" (or whatever you wish to call it).

     If it is a shock, Courant and Friedrichs do a fairly good job
     on a spherically converging shock wave.  You'll not find a
     panacea there.

     I cannot stress enough the importance of quantification in
     proposed physical models.  It is very easy to create mental images of
     things that are not physical, or do not have the consequences
     we mentally ascribe to them.

                               dale bass

--
C. R. Bass                                          [e-mail]
Department of Wildebeest
Transvaal                                           [phone]