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High-Temp Superconducting Tape
DrLudicrous writes "The NYTimes is running a little overview of the current state of mass produced superconducting materials. A company named Superpower (another blurb on them here) is making a layered superconducting tape out of ceramic materials- ceramics that are high-temperature superconductors (no resistance at liquid nitrogen temperatures, 77K). This is much cheaper to maintain than technologies based on superconducting metals, which tend to require liquid helium (~4 Kelvin) temperatures. A note of contention: the article mentions that superconductivity is not well understood -- high-temperature superconductors are not, but classical 'low-temperature' superconductors are well-described under the Bardeen-Cooper-Schrieffer (BCS) theory."
Man! We had that when I was in high school (late `80's)
Looks like room temperature superconductivity is impossible. Have we made any progress in new superconducting materials in the last 15 years?
That floating magnet experiment/demonstration they describe is one of the coolest physics phenomena I've witnessed, for those without subscriptions you chill the superconductor below its critical temperature and place a small magnet with high magnetic field strength to mass ratio above the superconductor and it floats or sits in mid air spining slightly, pretty cool to see.
This article is low on actual content, it fails to even mention what the Tc is for this tape. The highest Tc I'm aware of is in the 130K while room temperature is on the order of 300K. If we can find materials with high enough Tc and without bad qualities it will revolutionize the world, imagine an electric motor with near zero resistance, unfortunately it could be used for evil too.
Electrons are not bled out of materials as the temperature decreases. In semiconductors they do indeed become less mobile, increasing resistance, but in true conductors they become more mobile, as there are fewer lattice vibrations to get in the way (a simplistic metaphor, of course).
At extremely low temperatures the electrons pair up, which leads to superconductivity in metals. The amount of power which can be transferred is very high. These pairs are very easily broken apart, which is why superconductors are not perfect reflectors, any light breaks the pairs. IIRC it also limits the power that can be transferred over a superconductor.
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I don't know what you mean by bloody electrons (is that a British thing?).
As far as potential applications - they are numerous. Without thinking very hard a couple came immediately to mind.
(1) Electro-magnets - there are a lot of applications in medical and theoretical physics that require strong magnetic fields. Assuming that high-temp superconductors can be found whose properties don't break down under higher magnetic fields, superconductors could be used to create magnets stronger than any that we currently have.
(2) Particle detectors. If you have a superconducting loop and a charged particle passes through it, it will induce an EMF on the loop, causing a current to circulate. Since there is no resistance (i.e. no signal degradation), the current is much easier to detect and measure.
(3) MagLev anyone? Not on tape I guess, but levitating trains would be really nice. Then again, the previous ideas probably don't work very well with tape, but anything that helps move the field forward is bound to help.
I'm sure there are plenty of more interesting applications than these.
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High Tc superconductivity actaully has the begginings of a good theory to explain it.
In BCS theory, electrons interact with phonons (lattice vibrations) to coordinate into pairs and form bosons.
In much the same way, electrons in high Tc superconductors interact with spin waves in an antiferromagnetic material to coordinate into pairs and form bosons.
An antiferromagnetic material is one where the magnetic moments of neighboring atoms are opposite
up down up down up down up down up
You could imagine trying to move the middle electron over one position (trade with the electron to its right):
up down up down down up up down up
Now our magnetic order is screwed up, and this defect can propogate:
up down down up down up down up up
Each pair of "up up" or "down down" next to eachother is a spin wave, which is a boson, with a spin of 1.
Of course, really proving this theoretically is much harder, I don't think it's been done in 3D.
Interesting. Is copper really that expensive?
... and they have, actually. Copenhagen was the first, if memory serves. All of them quoted the capacity increase without digging as being the main reason. Per kA, it's probably more expensive, but the costs savings from not digging will probably make it cheaper over the lifetime of the cable.
Yes, actually. It's about $20-25/kAm right now.
But it's the recurring cost that's a big deal: at kiloampere levels, the power burned off by copper resistance starts to become more expensive than the cost of cooling. Since superconductors have strictly zero resistance, the cooling cost is fixed as the current scales, whereas it's linear in copper. At some point it becomes more economical.
The problem with high-Tc superconductors is that they have a current limit as well, and it's quite moderate, so the scale isn't quite there yet, when you work out all of the factors involved.
There are other reasons to switch, though: simply physical size: in Detroit, where they're replacing copper with superconducting cable in a few areas, they're replacing 18,000 pounds of copper with 250 pounds of superconductor - they replaced 9 cables with 3, and left 6 empty cable lines. This gives them 3 times the energy capacity without having to dig new cable lines at all.
The capacity issue is really what's been driving cities to replace them, though - digging new power lines, especially in cities, is simply ludicrously expensive, and so any option to replace with higher capacity lines without digging is a win.
So yes, really, they will replace copper with superconductors
Another saving with SC cables is volume. In many cities there is a severe space crunch in underground cable runs. Digging new ones is very expensive. If the SC cables have a higher average current density than conventional cables (and they do, even counting the space occupied by thermal insulation and coolant channels), then they can pay for themselves.
Do a search for "copper kAm" and you'll find the $20 /kAm figure. You're neglecting a ton of the production cost, and considering the *raw* copper cost is just $9/kAm, an additional $10/kAm for the rest of the cable is entirely reasonable. They don't just lay bare copper in the ground, after all. Most of the HTS figures they give show the rest of the cable costing about $10/kAm as well.
The $50/kAm figure for HTS cable is the final cost for the full cable, ready to lay in the ground.
As for the resistance loss vs refrigeration requirements, it's important to remember exactly how cheap liquid nitrogen is. *Very* cheap. In fact, going much higher in temperature really isn't economically important! I haven't seen any figures on "maintenance cost", but considering the resistive losses for copper can be large (at 1000A with the resistance of copper for a 0.8" diameter cable being ~0.02 ohms/1000', you're talking roughly 60W lost per meter) the refrigeration costs are going to be quite manageable.