Superconductors and induction - what are the posibilities?

[TomVok]

Hi all, I have a question which relates to induction and one potentially useful property of superconductors which seems to suggest one intriguing posibility. I won't say what just yet since my science is potentially a bit rusty, so don't want to sound like a fool.

As I understand it, after an electric current stops flowing through an inductor, the magnetic energy around the inductor's coil is absorbed by the coil, creating a spike in electrical energy. But what if the inductor's coil is made of a superconducting material, which if I understand superconductors correctly, is suposed to repel magnetic fields. When the applied current stops flowing, the residual magnetic field around the coil can not be absorbed as electrical energy so my expectation is that there would be a repulsive force between the residual magnetic field and the inductive coil, which may produce a kinetic force. Does anyone know whether this is true or not?

 

[Bobbywhy]

TomVok, Welcome to Physics Forums!

Your proposal was thought provoking. After a short Google search I may have learned the answer you seek: Superconducting inductors for temporarily storing energy is already a mature technology with some large-scale systems already attached to power grids to add large amounts of energy rapidly in case of large load fluxuations.
See: http://en.wikipedia.org/wiki/Superconducting_magnetic_energy_storage

Cheers, Bobbywhy

 

[TomVok]

Thanks for your reply, this is very interesting. I would not have thought of this as a means of storing electricity for any length of time. What I had in mind was slightly different - I was wondering if it might be possible to use this as a means of propulsion for spacecraft . Obviously this would require that the remaining magnetic field (after the electric current has ceast to flow through the coil), would need to be interacting with something in the space surrounding the coil that has mass - in order to be able to push against it to generate thrust. This makes me think of dark matter, although someone would have though of this and ruled it out already I would imagine. This is not really my area of expertise.

 

[Velikovsky]

The possibilities of superconductors are immense, especially those capable of operating at ambient temperatures. Imagine for one moment what it would mean if the 2 or 3 core cable on your domestic appliances were capable of carrying the electrical load from a 1000kVA generator. What that would mean in practice would be instead of using 30,000cc 7000Kg generator consuming 250 l/h to produce 1000kVA, you could use a 1000cc engine because an alternator made from superconducting "wires" could be made a lot lighter so the prime mover could be a lot smaller and use a lot less fuel. We do have supercooled superconductors but their practical uses are limited, the Japanese however are making fair progress with conductor's capable of 0 degrees C operation.

 

[0xDEADBEEF]

Superconducting coils try to uphold the field inside them. When a magnet is inserted in the normal conducting state, the set up is cooled down and the coil removed. A current will be induced in the superconducting coil such that the change of the field stays minimal. This resistance free current stays in the coil forever as long as it is cooled enough. Experiments have been done to see whether the resistance is really zero and the current has kept flowing for years without a measurable decrease. When you try to introduce a magnet into a superconducting coil it will produce a counter field due to the Meissner effect/induction. This in turn makes the coil and the magnet repel with some force. The idea that a superconducting coil and its field repel each other is only true insofar as there is a bit of magnetic pressure pushing the coil wire outwards, but this is true for any coil.