Undergrad Superconductor momentum conservation

[Danyon]

I often hear that a superconductor can hold a current indefinitely, I have a thought experiment which relates to this claim. Consider a closed square loop of superconducting wire, this wire carries some current. Will the electrons in the circuit transfer momentum and energy to the metal lattice when the electrons accelerate around the corners of the square circuit? If yes, then the current will actually slowly dissipate, if no then you could accelerate the electrons in the wire, giving a recoil force, and the electrons would travel all around the wire without transferring momentum where they can be accelerated again. This would be a momentum conservation violating thruster...So is current or momentum conserved?

 

[mfb]

Will the electrons in the circuit transfer momentum and energy to the metal lattice when the electrons accelerate around the corners of the square circuit?

Momentum yes, energy no (at least not once the coil reached an equilibrium position).
Momentum is conserved, you get should a tiny bit of tension in the wires balancing the momentum transfer of the cooper pairs.

 

[electro-physics]

I often hear that a superconductor can hold a current indefinitely

Does that mean the only limitation then will be current density of wire which has become supper conductor. I mean if current is less than its current density then it will feel no resistance and if current is more than its current density then some kind of resistance (friction) will come in practice?
Here I refer to current density as a relative term which depends upon frequency of operation due to skin effect and proximity effect.

 

[mfb]

Current density, external magnetic field and temperature form a region of superconductivity in the "corner" of low values for those three parameters.