# Levitating a magnet over a superconducting ring?

by cragar
Tags: levitating, magnet, ring, superconducting
 P: 2,422 Is it possible to levitate a magnet in a superconducting pipe or a ring? Is it possible to try to calculate this using the method of images and treat the magnet as a little current loop? Any input will be much appreciated.
 P: 2,292 Here's a few links which may be of interest to you: http://en.wikipedia.org/wiki/Magnetic_levitation http://arxiv.org/PS_cache/physics/pd.../0609141v1.pdf http://sprott.physics.wisc.edu/demobook/chapter5.htm
 P: 2,422 thanks for the links
P: 4,513

## Levitating a magnet over a superconducting ring?

This should give you the same stability as balancing one magnet over another where the poles are reversed. But any misalignment of axes will result in the magnet being pushed off radially. An array of superconducting loops over a surface may work as they approximate a superconducting surface.

I think this is an inexact approximation, where a large surface covered with small superconducting loops would allow freedom over the plane with velocity of the magnet unchanged from an intial velocity and the height fixed above the surface.
 P: 40 Yes, we actually do that at rino, a Dutch student organisation that goes around schools to inform kids about physics.
PF Patron
P: 2,140
 Quote by Phrak This should give you the same stability as balancing one magnet over another where the poles are reversed. But any misalignment of axes will result in the magnet being pushed off radially. An array of superconducting loops over a surface may work as they approximate a superconducting surface.
No, it is different. Remember that we are dealing with a diamagnetic effect here, so Earnshaw's theorem does not apply. Hence, it IS possible and it has been done, it is just very difficult if you are using a type I superconductor.

In most experiments (including the one in the above picture) type II superconductors are used. Here the magnet is "stabilized" by flux pinning which holds it in place (if you try to move the magnet it feels a bit like moving it in gel).
Note that the pinning can be "dynamic"; you are free to move the magnet (or the SC) as long as the field configuration stays the same. This is why it is e,g, possible make levitating model trains (with a SC in the "engine" levitating over a magnetic strip); when I was a PhD student we used a train to demonstrate superconductivity for visitors and undergraduates.
P: 4,513
[QUOTE=f95toli;3124576]No, it is different. Remember that we are dealing with a diamagnetic effect here, so Earnshaw's theorem does not apply. Hence, it IS possible and it has been done, it is just very difficult if you are using a type I superconductor.

In most experiments (including the one in the above picture) type II superconductors are used. Here the magnet is "stabilized" by flux pinning which holds it in place (if you try to move the magnet it feels a bit like moving it in gel). [\quote]

I've been curious about this. If it take energy to move it about, where it doesn't rebound in position, there is energy being dissipated somewhere. It seems it must go into heating the lattice, but I can only guess at the cause.

 Note that the pinning can be "dynamic"; you are free to move the magnet (or the SC) as long as the field configuration stays the same. This is why it is e,g, possible make levitating model trains (with a SC in the "engine" levitating over a magnetic strip); when I was a PhD student we used a train to demonstrate superconductivity for visitors and undergraduates.
By field configuration, I'm guessing you mean the orientation of the magnet. Is that correct?

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