In article ,
Rusty Hinge 2 wrote:

For an even stronger effect, take several miles of niobium wire and wind
on a hollow core so as to produce an axial field.

Seal windings in a case, and introduce liquid nitrogen.

When the temperature of the windings has equalised with the liquid
nitrogen, their electrical resistance disappears, and a current can be
maintained by only overcoming the back-e.m.f. of the system.

Oh, really? I think that you have the wrong gas :-)

High-temperature superconductivity hasn't yet reached the liquid
nitrogen stage - it will make a BIG difference if and when it does,
as the cost differential between liquid helium and liquid nitrogen
is large. Liquid hydrogen is intermediate, but a slight fire and
explosion risk ....


Regards,
Nick Maclaren.