> Like virtually all electrical wires, conventional superconducting magnets are fully protected by insulating material to prevent short-circuits between the wires. But in the new magnet, the tape was left completely bare; the engineers relied on REBCO’s much greater conductivity to keep the current flowing through the material.
Much greater conductivity than what? I assume there are other non-REBCO layers in the tape, but the article neglects to mention them.
If you have two resistors in parallel, the current in each is proportional to the ratio of the resistances. But what if one of the resistances is zero? Then all the current goes through that resistor. So if you have a superconductor in parallel with another resistor, all the current goes through the superconductor! Doesn't matter if the other resistance is very, very low, but still nonzero.
Reportedly some undergrad thought of this.
So the superconducting layer is bonded to stainless steel tape, which is strong, not brittle, and will go down to cyrogenic temperatures without problems. Most previous superconducting "wires" had brittle ceramic insulation, which was hard to wind into magnets.
I think there's another level to this, when you put a superconductor in contact with a metal there's a proximity effect that lowers the Tc of the superconductor. If you're using a superconductor that has a 4K Tc then you cannot afford to have your superconductor be weakened by the proximity effect. So the insulation is to prevent the proximity effect from happening.
Here, since you're using a much higher Tc material, if Tc is lowered by a few K you still have plenty of thermal budget, allowing you to take the hit from the proximity effect but be able to save on insulation.
The other thing the normal conductor does is save the coil from exploding if the superconductor quenches and loses its superconductivity (1/2 L I^2 can be a lot of energy). Old low Tc superconductors used copper for this, I believe.
Do any of these principles apply to liquid nitrogen applications?
The article outlines a plate design that incorporates steel/REBCO windings and cooling channels for liquid helium that seems to be modular and easily serviced.
REBCO is actually listed as a high-Tc material in the wiki below, but requires liquid helium.
If this were reworked into a liquid nitrogen design, could it reach 20 Tesla?
I think a better question is whether it's compatible with hydrogen, because 20K is plenty cold enough for REBCO, just not for classic Type-1 superconducting wire in magnets.
There is a layer of steel on the bottom that provides the structure for the tape and a layer of silver on top of the REBCO ceramic layer for electrical connection, but the whole tape is coated in copper which is the secondary conductor. When superconducting, the tapes, which are wound in a coil, carry the current and the copper acts as an insulator between tapes, but if it stops superconducting, the copper can become a resistive conductor which helps prevent quenching.
Much greater conductivity than what? I assume there are other non-REBCO layers in the tape, but the article neglects to mention them.