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EM waves transparent plasma

  1. Jan 21, 2014 #1
    Hi, recently I saw a great video about some scientists levitating small objects in mid air by trapping them in overlapping 180 degrees out of phase sine waveforms.
    It is easy to see that air is the medium through which sound can travel and sounditself being the vibration of air traps these objects placed at the way of these waves.
    just to be sure everyone gets my idea here , here is the video about the sound.

    So could such principle be used if I had plasma as a medium, like in a chamber of plasma and I wanted to float an object or some charges like electrons in the middle of it , assuming electrons becauce they are lighter than ions, protons and would probably respond for such external manipulation.
    I read that the plasma has it's specific frequency under wich it acts like a typical conductor and reflects the em wave and above which the em wave can penetrate the plasma, I assume this boundary is different for different plasmas depending on the density of the plasma and temperature am I correct here ?

    So if I would have my plasma of whatever shape and I wanted to float an object inside of it , could I use the em waves at and above the specific frequency to achieve something similar to this in what they achieved with audio waves?
    I am asking this from a theoretical standpoint , so doesnt matter if objects cannot be in a plasma because of the heat and other factors dont play a role here.
    Last edited by a moderator: Sep 25, 2014
  2. jcsd
  3. Jan 24, 2014 #2

    Claude Bile

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    A similar effect (albeit on a smaller scale) can be achieved using laser light - commonly referred to as "optical molasses".

  4. Jan 24, 2014 #3


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    It's a bit weird to talk about levitating ions and electrons using a plasma because a plasma is made of ions and electrons. It's pretty hopeless to try to track individual electrons or ions, so it doesn't make sense to talk about levitating specific electrons. But, it is possible to get a localized region of higher ion and/or electron density using plasma waves. There's a lot of research in plasma confinement and transport done by the fusion community.

    As far as a macroscopic object, I think it is possible, but I don't know of any examples off hand.

    There are many kinds of waves that can propagate through a plasma at different frequencies and wavelengths, depending on the density, temperature, and magnetic field. It's quite complicated.
  5. Jan 24, 2014 #4
    I appreciatte the replies.
    Why using a plasma ? I know plasma consist of ions and electrons but , okay maybe i wasn't clear enough , I was thinking about a method of confining electrons in the middle of a plasma sphere, so I was asking would it be possible using EM waves of certain frequency like the sound waves were used in the video to achieve levitation of objects.

    Ofcourse the difference here is that sound uses air as a medium and levitates physical solid objects.
    Plasma on the other hand is not solid and the temperatures and kinetic energies of particles involved complicates the matter.

    But when we consider em waves traveling inside a plasma we do say that the electrons are the carriers of the induced current just like they are in metals due to their lower mass as compared to the ions, is that correct?

    So I wonder , in a Polywell design they try to make a negative potential well in the middle by keeping the electrons there by magnetic fields , stationary ones I assume.
    Could electrons be confined in a region by using em waves to sort of levitate them in the middle?
    I hope you guys understand the idea I'm telling here. :)
  6. Jan 24, 2014 #5


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    Crazymechanic, there may be one thing you are overlooking when you are asking how to "confining electrons in the middle of a plasma sphere": each electron is negatively charged (as you know), so once you try to confine them they repel. The more you try, the more they resist.
  7. Jan 25, 2014 #6
    they do repel yes, so the negative potential well is limited by the strength of the magnetic field.
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