Superconducting material has a rating for critical field intensity

1. Oct 20, 2008

trilex987

Hi, here is a couple of questions about superconductors

Each superconducting material has a rating for critical field intensity. Now, does the field generated by its own current count?

And also what is the current superconducting (type II) material with highest current densities achieved?

And third question. If you have a superconducting material with an already initiated current, and you put some kind of a load on top of it (to levitate), would there be a counter-effect on the current inside the superconductor, meaning, would the current slow down due to the force between the two objects.

2. Oct 20, 2008

f95toli

Re: superconductors

Yes, this is in fact what determines the critical current density.

I am not 100% sure and obviously it depends on the temperature; but I am pretty sure the latest version of YBCO cables hold the record at both 4.2K and 77K.

I can't see why this would happen, obviously the field distribution would change but the speed of light in the superconductor shiuldn't (at least not much, although there would presumably be small local effects due to change in field).

3. Oct 20, 2008

trilex987

Re: superconductors

No, no, sorry, I formulated my last question incorrectly, I meant would the load cause a counter-potential which would reduce the current in the superconductor.
In other words, after you induce current in the superconductor, would you need a power source to keep the object above levitating, or is it a state of balance in which the current keeps on flowing for ever (in theory) and the object will always stay in its levitative state.

4. Nov 11, 2008

Enthalpy

Re: superconductors

Trilex, did we met somewhere else? Anyway, my answer will be the same.

When you put a load over the coil, the magnetic flux remains the same. As your levitating object repels the field, the induction must increase elsewhere, which means that the current increases in the coil.

This is consistent with the energy brought by the falling mass of the levitated object.