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Hovering magnet over superconductor/superconductor over magnet

  1. May 9, 2014 #1
    Hey, everyone.

    I'm in my final year of my bachelors at uni and we have a class that's basically to teach us how to set up a research project (among other things). We've already done the lit review, a risk assessment, all of that jazz. The final assessment is to basically produce an informative poster for a presentation that a bunch of people from various industries are going to attend.

    Our topic is on high temperature superconductors (specifically cuprates). I suggested to my team members that we should actually demonstrate something like the Meissner effect or flux pinning (quantum locking) on the presentation day and everyone liked the idea. After having a chat with the head of the physics department he bought us a little superconductivity demonstration kit which comes with a small, thin piece of YBCO as well as a tiny, 3.2 mm diametre neodymium magnet. Because the magnet is pretty damn small I want to instead get a much larger magnet, cool the super conductor down in liquid nitrogen, and then place the superconductor over a big magnet (instead of submerging the superconductor in liquid nitrogen and hovering the magnet over the top). I hope that this type of arrangement would be easier to see from a distance, and would allow for a greater degree of separation between the magnet and the superconductor.

    I guess my questions are;


    1) Is this possible? I don't see why not. There appears to me to be no fundamental difference in the physics whatsoever by merely turning the whole apparatus upside down in effect (hovering the superconductor over the magnet instead of the magnet over the superconductor).

    2) If so, what kind of sized and strength magnet would be needed (ballpark figure) to ensure adequate lift (the superconducting plate is rectangular measuring 34 mm x 18 mm, and probably 1 - 2 mm thick at most). If the magnet which the superconductor is hovering over isn't sufficiently large I feel as though the superconductor might slide out of place (I might be completely wrong there, though).

    3) If the above arrangement is possible, considering the superconductor is very thin (and a type-II superconductor at that), is it reasonable to assume that flux pinning will occur, or will it only be the Meissner effect that we can demonstrate.

    4) Finally, as the superconductor begins to heat up again what would be expected to happen? Would it drop abruptly onto the magnet below, or would the repulsive force begin to lessen and would it gradually lower down onto the magnet?


    I'm going to test a few arrangements out on Monday when I head to uni, but if there's any major don't it'd be great to hear them in advance (and if there's any incredibly awesome, "definitely do this!"s then I'd obviously love to hear them, too).
     
  2. jcsd
  3. May 9, 2014 #2

    f95toli

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    Yes, but the problem with this arrangement is that the superconductor warms up pretty quickly unless submerged in LN2.

    My guess would be that a "normal" neodynium magnet would be strong enough. If you cool the supeconductor down in field (with a spacer between the magnet and the SC until it starts to levitate) the flux will "lock" the SC into place so it should not "fall off".
    You'd have to try it to make sure.

    You will in practice always have flux pinning in YBCO.

    It slowly drops as it goes through Tc. How slowly depends on how quickly the temperature is going up and the width of the transition (which for something as large as this will probably be 1-2K)
     
  4. May 9, 2014 #3
    Thanks for the info, f95toli. On your answer to question 2, though; from videos I've seen it appears that you can simply place a chilled type-II superconductor into a magnetic field, let it go and flux pinning will do its thing. Why the need for a spacer, then?

    I'm thinking of this video in particular:

     
    Last edited by a moderator: Sep 25, 2014
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