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In this answer to "Inductor made out of super conductors", the experiences recounted included "ramping up the inductor" or "charging it up". Absolutely fascinating is the thought of two currents continuously flowing -- the electrical current inside the superconductor, and the magnetic current inside the ferrite.

I know that every normal conductor has an electrical resistance, and that the electrical resistance is mostly removed in the superconducting conductor.

It is my understanding that there is also a "magnetic current" flowing in the ferrite of the superconducting inductor. (I don't remember where I heard this.) I know that there are losses involved with changing the amount of that flowing current. But if the superconducting current is a full short-circuit, and is therefore "holding", that is, maintaining the flow of current without loss, then...

Is there another efficiency loss, similar to electrical resistance, that affects the continually flowing magnetic current, assuming that the magnetic current is not changing at all in magnitude? Is there magnetic resistance?


This is my guess: even though I have been told that a magnetized inductor has a magnetic current flowing, the stored magnetic field to me seems more like a coiled spring, not in motion, but yet still "containing" potential energy. Hence, my guess is that there is no resistance because there is no motion. The action of compressing or uncompressing the spring is more of a kind of motion that shows a kind of "resistance" in the hysteresis losses, actual crystal deformation if I am right. What confuses me is the flux, which seems like a flowing fluid. Please either confirm or correct my concepts of these things. Thank you.

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    \$\begingroup\$ Magnetic flux is stationary, but acts sort of like an elastic band - it wants to take the shortest path even if it's not actually moving. 'Reluctance' is the resistance of a material to having flux pass through it, so the magnetically shortest path might not be the physically shortest path. \$\endgroup\$ – SomeoneSomewhereSupportsMonica Jul 19 '20 at 5:48
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The magnetic field is a vector field that forms loops, but there is no actual "magnetic current" — nothing that "flows" along those loops.

Yes, there is energy (work) associated with changing (increasing or decreasing) a magnetic field, but the only losses would stem from the electrical losses associated with secondary ("eddy") currents in nearby non-superconductors.

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    \$\begingroup\$ There would be losses from the hysteresis of the magnetic material also. \$\endgroup\$ – AJN Jul 19 '20 at 2:50
  • \$\begingroup\$ There is current consumed to keep superconducting magnets very cold, close to absolute zero. \$\endgroup\$ – user105652 Jul 19 '20 at 3:46
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    \$\begingroup\$ @AJN Hysteresis losses only occur when changing the magnetic field. For a static field, like around a superconductor, there is no change in the field so no hysteresis loss. \$\endgroup\$ – SomeoneSomewhereSupportsMonica Jul 19 '20 at 5:42
  • \$\begingroup\$ Thank you. I wanted to know that "there is no actual 'magnetic current' — nothing that 'flows' along those loops." The other thing I really wanted to know is if there were any parasitics (other than hysteretic) that "leak" from the flux (but since nothing "flows", there must be no "friction"). Can you confirm? \$\endgroup\$ – MicroservicesOnDDD Jul 19 '20 at 20:47
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The magnetic field caused by the current flowing in a conductor causes an image current to flow in the surface of nearby superconductors which prevents the magnetic field from penetrating the superconductor to any distance. This occurs even at DC.

Ferrites have high resistivity so no persistent current can flow (at a macroscopic level).

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  • \$\begingroup\$ What kind of "current" flows in a magnetic circuit? Is that the flux? And are there losses in whatever is flowing? \$\endgroup\$ – MicroservicesOnDDD Jul 19 '20 at 15:34
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    \$\begingroup\$ An external magnetic flux causes a surface current to flow in a superconductor, causing in turn, a counteracting flux that excludes flux from the bulk of the superconductor. If the current in the superconductor is caused by a wire carrying current we can speak of an "image" current, kind of a mirror image of reversed current. See, for example, this Physics SE answer. \$\endgroup\$ – Spehro Pefhany Jul 19 '20 at 18:21
  • \$\begingroup\$ Would these "reflected" fluxes (antifluxes? contrafluxes?) cause any associated parasitic losses? Thank you for answering. Another fascinating aspect. \$\endgroup\$ – MicroservicesOnDDD Jul 19 '20 at 20:51
  • \$\begingroup\$ It's a superconductor so there are no measurable DC losses, but changes will cause losses from eddy currents in any non-superconductors and probably EM radiation. Superconducting resonators have high Q, but not infinitely high. Flux jumps also cause some hysteretic losses. \$\endgroup\$ – Spehro Pefhany Jul 19 '20 at 21:02

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