Pinning Force & Electromagnetic Drag Force

[labview1958]

In the meissner effect the magnet "floats" on a superconductor. A small magnet would actually stay in one position as if it is "pinned" there by a mysterious force. The magnet would "resist" if we try to"pluck" it from it's position. Is this "pinning force" same as the electromagnetic drag force experience by a magnet floating on a spinning copper disc?

[5614]

The Meissner effect is what happens to a superconductor when it is below critical temperature. What happens is that the magnetic field is all external to the actual superconductor... all of the magnetic field is on the outside whereas normally (above the critical temperature) it would be inside the superconductor as well as outside.

 

The "floating magnet" on top of a superconductor is an example of the Meissner effect in action. What is happening is that the permament magnet is being repelled from the superconductor due to the Meissner effect.

 

The other thing I don't fully understand is something called flux pinning where basically the magnetic field becomes trapped or held in place which is what stops the magnet from sliding away from the superconductor.

[DQW]

Flux pinning in a Type II SC happens when the SC is in the Abrikosov phase. This is a phase that is intermediate to the Meissner phase and the normal phase. When you increase the temperature or field from the Meissner phase in certain types of SCs, the SC finds that it is energetically less expensive to partially allow some of the field through it (than to exclude the entire field or allow the entire field). So, rather than remain in the perfect Meissner phase or turn completely into a normal material, the SC nucleates tiny lines of normal material that carry flux through them. In a perfectly defect-free SC crystal, these lines, known as flux vortices, arrange themselves along a triangular lattice. However, in a real material (with impurities and defects), these vortices get pinned at the locations of these defects. This is what is known as flux pinning in Type II SCs, and is what helps stabilize a levitation demo.

[labview1958]

I understand the magnet is "held" in position. An external force is needed to "remove " the magnet. The superconductor will try to "resist" the magnet being "pulled" away. Thus the flux pinning will increase to it's maximum before losing to the "pulling" away force. Is this pinning force similar to the electromagnetic drag force?

[labview1958]

Is it possible to measure the pinning force. I measured the electromagnetic drag force like this.

http://img102.imageshack.us/my.php?image=rotatingcoppermagnet0an.png

 

Can the same method be used to measure the pinning force?

[labview1958]

I have come across a diagram, I believe describe the "pinning force" on a certain type of maglev. It looks as if the "pinning force" is similar to the electromagnetic drag force. Is my assumption valid? Here is the diagram.

 

The superconductor is moved over a series of magnet. The forward movement is the centrifugal force.

[labview1958]

Anyone interested in discussing superconductivity pinning force? Is there a better forum?

[labview1958]

Which type II superconductor has the strongest pinning force? Where can I find the ANSWER?

[labview1958]

Is there a formula connecting the levitational (lorentz) force of a bulk superconductor with it's pinning force? Does the pinning force increases with the lorentz force? Where can I find the answer?