I was thinking about building an electric motor using superconductors and I have some general concept questions in regards to how the behavior might be different from ordinary wires.
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The Meissner effect, expulsion of magnetic fields from the superconductor. If you construct a solenoid out of superconducting wire does this Meissner effect significantly change the field pattern compared to a regular wire solenoid?
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If a solenoid is created out of superconducting wire is the current limited to the magnitude of the magnetic field it creates because if the magnetic field strength is too large it will return the superconductor to a non superconducting state?
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If you have a superconducting wire with a current flowing through it and you expose it to a magnetic field does it still experience a force (obeying the same rules as a regular wire with current flow) or because of the Meissner effect the magnetic field never reaches the current carriers and so no force is experienced? Or is there only a fraction of the expected force experienced because the magnetic field does not penetrate through all the current carriers?
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If you have two or more strips of superconducting tape stacked on top of each other with current flowing in the same direction through them and then you have a magnetic field strength probe and you probe the space above the stack, would the field be just the sum from each strip or would the Meissner effect in the strips closer to the top surface cause magnetic shielding of the lower strips and so the real magnetic field strength near the surface of the top strip would be less than the sum of the magnetic fields from each current carrying strip?
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Is current flow in a superconductor only a surface effect? (i thought it was) Why did I see one company selling 3D wires? is that really isolated 2D stacks?
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Is the only way to make a loop of superconductor run a continuous current is by induction?
Thanks for reading and thanks in advance for any responses.
Best Answer
For question number five, the answer is it depends on the type of superconductor. For type I superconductors, the superconducting carriers are ideally only running along the surface of the material in a layer called the London penetration depth. For type II superconductors, the carriers start on the surface, but can ultimately use the entire volume. There's a mathematically accurate model of this called Bean's model. Basically as each layer of the superconductor hits reaches its critical field, (or critical current), the next layer begins carrying current. The diagram1 below describes the model briefly.
References 1. Bean, C., "Magnetization of High-Field Superconductors", Rev. Mod. Phys., 36, (1964), 31