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I Acoustic electron trap question

  1. Mar 10, 2018 #1
    Hi, I wonder is it possible to trap electrons in vacuum using acoustic waves as it is possible to trap them using electromagnetic waves?

    imagine a vacuum tank and electrons injected say from a thermionic emission (electron gun) and having one or two transducers set apart to produce satnding waves, would the electrons be concentrated in sort of electron clouds much like water and other fluids can be levitated and trapped with the help of such acoustic standing waves?

    my own guess is this works with lightweight solids because they are light and don't repel each other but since electrons repel one another I think it would be hard to confine them with an acoustic standing wave trap, is that correct?
     
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  3. Mar 10, 2018 #2

    sophiecentaur

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    There can be no acoustic waves in a vacuum but you can make electrons bunch together using electromagnetic fields. See Klystron and also the travelling wave tube amplifier.
    Mutual repulsion is what limits the degree of bunching that can be obtained.
     
  4. Mar 10, 2018 #3
    oh damn right , sorry I forgot to mentioned another important part, sure sound doesn't travel in vacuum as in the famous saying "they won't hear you scream in space" :D

    I was thinking say the vacuum is filled with a gas like hydrogen and say that gas is ionized at certain energy/temp so plasma is a rather good electrical and heat conductor, would it also conduct acoustic waves? and then since electrons are much lighter than protons would it be possible for the electrons to form clusters in the path of the standing waves?


    maybe the electron density could be achieved higher if the acoustic standing waves were coupled with precise EM standing waves to form a double trap, since acoustic and EM waves don't interfere destructively with each other could they add up their confinement power if being in phase?
     
  5. Mar 10, 2018 #4

    Vanadium 50

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    Then it's not a vacuum.

    I think you should carefully think about what you want to do, and what the definitions of those things are (what does it mean to be "in vacuum" or "trapped") and re-ask your question.
     
  6. Mar 10, 2018 #5

    anorlunda

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    Are you working on a SF story with this idea?
     
  7. Mar 10, 2018 #6

    ZapperZ

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    Unfortunately, it now appears as if you're making things up as you go along.

    If you're using a plasma, then you will need EM waves to modulate that plasma, not via some "transducers". If this is true, then why bother with having a plasma, since we can already modulate or trap electrons in EM waves by itself? It appears that using such a plasma as a medium is a highly inefficient way of doing such a thing. And this is BEFORE we look at the complexities of plasma (i.e. higher order perturbations, self-induction, etc.). You should never introduce something that you do not have a good knowledge of.

    BTW, if a volume has a high-enough density of gas to generate acoustic wave, then electrons will no longer have very long mean-free path, i.e you've left the molecular regime and gone into the viscous regime. Your electrons in such an environment will continually scatter off these gasses, making trapping them almost impossible.

    Notice how, by trying to solve one problem with your scenario, you've created a whole bunch of other new problems?

    Zz.
     
  8. Mar 10, 2018 #7
    first of all I am happy to create problems as this is just a thought and my goal is to think and learn.
    I do apologize for rushing the question in the first place as I made some thought errors that I know very well myself like vacuum isn't a medium for sound to travel through.


    Now here is why I asked the question. Some time ago I was reading up on anything that had to do with nuclear fusion, Bussard tried really hard to perfect the Hirsch and Farnsworth fusor which in itself being an Inertial electrostatic device is as simple as it gets. Well obviously the inner grid suffers immediate damage and is degraded quickly also the plasma serves as a thermionic diode shorting the power supply. So they made the Polywell, I'm sure you guys are familiar with it so fast forward I was looking at a bunch of youtube vids about acoustic levitation, they attracted my attention because you can levitate an object with very little power.
    well the object is small true and the power of confinement is also not that large.
    But then as I think about it the pressure of plasma inside is very small so the acoustic waves would have a very bad medium to work through and that would probably weaken them to the point of them being barely noticeable, so there would be almost no help from them to the B field in trapping the electron well.
    I think you see where i'm going with this.


    when anorlunda asked whether i'm working for an SF with this that was the moment I realized how stupid my question sounded... :D


    Ok but all in all how does a plasma react to such low frequency waves as acoustic? if the plasma density is say high enough would such acoustic waves if strong enough be able to affect say electrons in the plasma? Or when their ionized is their kinetic energy so high that an acoustic wave no matter how strong simply cannot influence them because their mass is so small and kinetic energy so large and since acoustic wave can only influence matter by its surface size and mass properties the acoustic wave couldn't change the electrons trajectory/behavior?
    I assume it also would probably depend on the acoustic frequency used.
     
  9. Mar 11, 2018 #8

    jasonRF

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    You haven't given enough information to even begin answering your many questions. Is this a "good" plasma that has few collisions, or is your plasma collisional (perhaps interacting with neutral fluids that have their own dynamics)? Is there a magnetic field? When you say "low" frequency, what are you comparing the frequency to in order to call it low (electron or ion plasma frequencies, electron or ion cyclotron frequencies, ...)?

    Even if you did give all of that information (and much more) you are asking for a course in plasma waves. Note that particle trapping / wave-particle interactions are not in the linearized theory, so you are in the realm of nonlinear plasma physics.

    If you have a specific question we may be able to help, but it sounds like you need to learn some plasma physics before you even know what to ask.
     
  10. Mar 12, 2018 #9

    Khashishi

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    Waves in plasmas are kinda complicated. Some solutions will combine properties of electromagnetic waves and sonic waves.
     
  11. Mar 13, 2018 #10
    well if we are talking about sound waves, I assume their effect would be very small in plasma due to the low density in a plasma that is found in a fusor or other devices, correct?
    because sound waves move better in denser mediums atleast that's what I read about sounds in water/ocean or solids like metals.

    from a physics perspective say we somehow have a plasma that is very dense like those found in stars etc, so for the sake of argument let's say that our plasma density is that of water, in which medium sound waves would lose less energy and travel better? I am asking this because densities being the same water has much lower particle kinetic energy than a plasma so I am not exactly sure how particle kinetics affect this if density is similar
     
  12. Mar 13, 2018 #11

    jasonRF

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    In a plasma the acoustic-like wave modes (and there are several) have longitudinal electric fields associated with them, which of course can exert large forces on electrons. Khashishi alluded to this a few posts back.

    Edit: I am not sure what exactly you are trying to figure out at this point, but I do know that you are not going to figure this out without working through the equations. Even if you figure out a plasma configuration that satisfies what you are looking for you then need to analyze it to see whether it is stable or if it quickly breaks up into some other configuration. By the way, there are certainly plasma waves that trap electrons and drag them along. Is that all you are looking for?
     
    Last edited: Mar 13, 2018
  13. Mar 13, 2018 #12

    Vanadium 50

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    I have no idea what the question even is anymore. It's a gas! It's a vacuum! It's a vacuum filled with gas! It's a plasma!
     
  14. Mar 13, 2018 #13
    I understand your objections, but please bear with me. the problem is I myself don't know fully what I'm asking.
    as i said it is because I saw two different phenomena in physics and simply thought to myself that maybe they can be combined to create something useful, as I already explained about the fusor and later adaption named polywell which tried to create a potential well with electrons held in place by a magnet coil arrangement, I was just thinking that maybe the electromagnetic field used to create the potential well with electrons can be arranged together with the acoustic waves of specific wavelength so that they help in the electron confinement,
    sadly as you guys already pointed out I lack the specific plasma physics background to be able to answer such a question myself which I think is a rather complicated one, so that is why I asked this question.

    forget the vacuum, that was simply me writing and thinking at the same time so made a simple mistake.
     
  15. Mar 13, 2018 #14

    Vanadium 50

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    Then how do you expect us to answer it?
     
  16. Mar 14, 2018 #15
    Well i did gave context to my question both in the last post and also in atleast one before, does the question seem reasonable as explained in my last post?
     
  17. Mar 14, 2018 #16

    jasonRF

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    Which question? You have asked a number of them in this thread; the post you are referring to has no questions. If you post a clear question I can try to answer.
     
  18. Mar 14, 2018 #17
    ok well then please look at my post #13 I basically explained the fusor/polywell approach , I am sure you know the fundamentals of those devices and their setup, so my original idea was with regards of incorporating the acoustic standing wave phenomena into the polywell magnetic electron trap, because the electron well suffered a major drawback as the electrons escaped with time and hit the positively charged magnet casings and so caused some problems, I wasthinking if the magnets could be rearranged and such acoustic standing wave phenomena incorporated to maybe somehow increase the effectiveness of the electron trap creating the potential well.

    then I started to backtrack because I sort of realized these devices have a very low plasma density and although I don't know for sure as I am not that wise about plasma specific properties I sort of think that acoustic waves perform better if the medium they travel through is thicker rather than less dense?


    Ok I think you get the idea, thanks for participating:)
     
  19. Mar 14, 2018 #18

    jasonRF

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    I think I now understand the general thing you care about. Did you do a google search? I googled: plasma polywell acoustic wave

    On the first page of results I found

    https://dspace.mit.edu/bitstream/handle/1721.1/29869/31763419-MIT.pdf

    Section 5.4 makes it clear that this idea has been examined at least a little bit. Note that "acoustic" waves in a plasma have electric fields associated with them, and it is the electromagnetic fields that have the large impact.

    Please do your own google search.

    Also, this is a research topic you are thinking about. An expert would likely need hundreds of hours (or more) to investigate the idea in the detail required to know if it makes any sense at all.

    Jason
     
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