The summary is as follows:
1. Superconductor toroid (ring) said to be able to allow a circulating current for a relatively long time (I read anything between 10-1000 years - take your pick).
2. Assuming that a current is "electrons moving", will create a magnetic field.
3. Assuming that this magnetic field has a shape (normally seen as a bell), this magnetic field will have a definite size. Someone suggested to me that magnetic field may be static like in a permanent magnet. I don't know but I have been doing a little thought experiments and suggest that the effect may be the same but the mechanism of each differs .
Thought experiment: I run a superconductor cable ring 300 million metres in circumference. I believe that if one measures the magnetic field at one point on the ring, one should see that you will see a a peak once a second (I have heard that velocity of current is 80% speed of light).
4. Superconductors have a critical magnetic field. If external field larger than this, the superconductor current will be quenched. If external filed smaller than this, superconductor current not quenched or should be protected by Meisner effect.
Essentially, the idea is to tap the magnetic field but there are some limiting conditions which I can go through if required (this is a summary and to be honest I am a bit tired of talking about this :D)
A number of ways possible (AC and DC)
DC way is to put probes close enough to the surface of the superconductor. These probes will have an magnetic field induced on them. The more probes, the more power (I read that magnetic fields >100 Tesla now).
AC way is a little more difficult to explain without a picture so I have attached one. Please refer. The idea is that should a single directional current be moving through a single ring based on the shape provided, one should see an AC current like effect in the superconductor (say measuring it at the points where the figure 8 meets the ring).
Anyway, this is the power source. This reminds me that E=hf. The smaller the ring, the greater the amount of energy able to be derived from it. It is possible that it is even the solution to Neal Stephenson nano power batteries.
Reading somewhere near the end of the attachment, it is noted that an SC can be a DC generator.
Please see "Fully baked innovation" Superconducting rotory toroidal transformer.