Shielding magnetism with superconductors

In summary: Thanks for the correction!In summary, the conversation discusses the blocking of magnetic fields by a superconductor. It is explained that if the superconductor is placed around an already existing magnetic field, it will shield it off via the Meisner effect. However, if the superconductor is in the superconducting state before the magnetic field is created, it will preserve the previous amount of flux due to the induction of Eddy currents, which do not dissipate in a superconductor as they do in a conductor. The conversation also mentions the use of superconducting shields to trap existing magnetic fields. It is clarified that the Meisner effect is responsible for shielding the magnetic field, not Ampere's force law.
  • #1
Danyon
83
1
If I surrounded a wire carrying current with a superconductor would the magnetic field from the wire be blocked from the outside?
 
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  • #2
If while the current is flowing, you surround it with a superconducting material, then no, it doesn't block the magnetic field. But if you surround the circuit with the superconducting material first and then start the current flow, then yes, it will block the magnetic field.
 
  • #3
Shyan said:
If while the current is flowing, you surround it with a superconducting material, then no, it doesn't block the magnetic field. But if you surround the circuit with the superconducting material first and then start the current flow, then yes, it will block the magnetic field.

What's the difference between the two scenarios that causes this?
 
  • #4
At first I should correct that the material shouldn't be in the superconducting state before placing it there. So how it should be done, is first surrounding the circuit with the material, then cooling the material for it to make transition to the superconducting state and then start the current flowing.
Drakkith said:
What's the difference between the two scenarios that causes this?
A material in the superconducting state tends to keep the magnetic flux through it, constant. So if, when enters the superconducting phase, there is no flux through it, its going to keep the flux zero. So when you start the current flow and the magnetic field is created, the material will induce currents in itself to cancel the magnetic field from the circuit and keep the flux constant(which is zero in this case).
 
  • #5
Shyan said:
At first I should correct that the material shouldn't be in the superconducting state before placing it there. So how it should be done, is first surrounding the circuit with the material, then cooling the material for it to make transition to the superconducting state and then start the current flowing.

A material in the superconducting state tends to keep the magnetic flux through it, constant. So if, when enters the superconducting phase, there is no flux through it, its going to keep the flux zero. So when you start the current flow and the magnetic field is created, the material will induce currents in itself to cancel the magnetic field from the circuit and keep the flux constant(which is zero in this case).

This is confusing. It appears that you are mixing up superconductivity with perfect diamagnetism.

It doesn't matter if the there is already a magnetic a field or not. A superconductor will shield off the magnetic so field via the Meisner effect, IF the superconductor is a a Type I or below the lower critical field.

Zz.
 
  • #6
ZapperZ said:
This is confusing. It appears that you are mixing up superconductivity with perfect diamagnetism.

It doesn't matter if the there is already a magnetic a field or not. A superconductor will shield off the magnetic so field via the Meisner effect, IF the superconductor is a a Type I or below the lower critical field.

Zz.

The point is, when a flux through a conducting material is turned on, Eddy currents are induced in it that, by Lenz's law, oppose the changing of the flux from zero to that finite value. But those currents are dissipated away in a finite time in a conductor. But if you do the same thing to a material in the superconducting phase, the Eddy currents won't go away so they will preserve the previous amount of flux.
 
  • #7
One way of showing it in most superconductivity books, is through the following diagram:
fig4.gif
 
  • #8
I think surrounding a existing magnetic field with a superconducting magnetic shield can create a flux trap pinning the existing field. I remember reading something about it when looking at shielding methods for electron microscopes.

Did a google search and found something similar: Superconducting Shields
 
  • #9
Does Amperes force law apply to superconductors?
 
  • #10
ZapperZ said:
This is confusing. It appears that you are mixing up superconductivity with perfect diamagnetism.

It doesn't matter if the there is already a magnetic a field or not. A superconductor will shield off the magnetic so field via the Meisner effect, IF the superconductor is a a Type I or below the lower critical field.

Zz.

I studied superconductivity a while ago and it seems I don't remember it well. Sorry for the wrong information, to others in the thread as well.
 

1. How do superconductors shield magnetism?

Superconductors have the ability to completely expel magnetic fields from their interior. This is due to the Meissner effect, where superconductors create opposing currents to cancel out the external magnetic field.

2. What are the benefits of shielding magnetism with superconductors?

Shielding magnetism with superconductors has many practical applications. It can be used to protect sensitive electronic equipment from magnetic interference, create more efficient MRI machines, and reduce energy loss in power transmission lines.

3. Can superconductors completely shield all types of magnetism?

No, superconductors are not able to shield static magnetic fields completely. They can only shield dynamic or alternating magnetic fields.

4. Do superconductors have any limitations in shielding magnetism?

One limitation of using superconductors to shield magnetism is that they are only effective at very low temperatures. Once the temperature rises above their critical temperature, they lose their superconducting properties and are no longer able to shield magnetic fields.

5. Are there any potential risks or drawbacks to using superconductors for magnetic shielding?

While superconductors have many practical applications, they can be expensive and difficult to produce. Additionally, the extreme low temperatures required for their superconducting properties to work make it challenging to use them in certain environments.

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