Alaric B Snell wrote:

Jon Elson wrote:

No, it is really just hundreds of amps. They have to "ramp up" such
a magnet with a non-superconducting power
supply, with non-superconducting cables, so the currents outside
can't be enormous. Therefore, there's no
way to get enormous currents INSIDE the superconducting part. But,
it doesn't matter, as they just add more
turns of the superconducting wire. The flux can add up to millions
of amp-turns, however.


Ok, cool.

*thinks*

How does one define the energy content of a ramped-up magnet? The
problem with superconductors is that I'm familiar with nice ohmic
devices. Big current round the coil, but no voltage, so no power
transfer - that's fine, it's a uniform energy density and it's not
changing.

But how does one work out an energy from that? I feel the inductance
of the coil must be involved somewhere...

The energy is in the field, not the winding. So, winding current
doesn't mean much. It is the total
number af amp-turns, and the volume of the interior of the solenoid. If
it has an external iron
shield, that lowers the energy, I think. (I'm more used to working with
iron-core inductors with
small air gaps, so these things are a bit far from my general experience.)

Of course, you can just measure the inductance!

Jon