Shielding magnetism with superconductors

[Danyon]

If I surrounded a wire carrying current with a superconductor would the magnetic field from the wire be blocked from the outside?

 

[ShayanJ]

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.

 

[Drakkith]

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?

 

[ShayanJ]

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.

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).

 

[ZapperZ]

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.

 

[ShayanJ]

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.

 

[ShayanJ]

One way of showing it in most superconductivity books, is through the following diagram:

 

[nsaspook]

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

 

[Danyon]

Does Amperes force law apply to superconductors?

 

[ShayanJ]

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.