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New Superconductor Found "Immune To Magnetism"
Lisandro sends in news that testing of the new class of superconductors we discussed a while back (compounds of iron, lanthanum, and rare earths) has turned up a major surprise: magnetism doesn't shut off the superconducting state. Magnetic fields represent one of three factors that limit expanded applications for superconductors (the others are current density and temperature dependence.) The research will appear in Nature; here's a preprint (PDF).
I seem to recall that one limit was simply the ceramic nature of most superconductors. If it isn't ductile, you can't use it for wires -- which are kind of important for most superconducting applications. Am I wrong about this?
Make cheese not war 8:)
Perhaps now we can have internal resistanceless batteries!
I knew this a few years ago. I was thinking about super conductors and magnetic states and thought "huh, how about that". I recall getting up to get a breakfast burrito.
Since then, no one has asked and I haven't even thought to mention it.
Oh well.
Scanning the paper, it seemed to have little bearing on this magnetic field tolerance, but rather talked about the effects of grain boundaries. Did anyone understand how the paper related to the press release?
"Ah Crappp!!!" - Magneto, 2008
Since when does Lanthanum not belong to the rare earths anymore?
Ah, kdawson posted it, that explains everything.
Read that preprint, or at least look at the pictures -- specifically Fig. 6. It's a measurement of the upper critical field (i.e. the magnetic field that destroys the superconducting state) versus temperature. The 90% line (where the resistivity is 90% of its normal-state value) does indeed go off the graph at low temperatures; it extrapolates to about 60 T for 5 K.
There's a big difference between "This material has a very high critical field" (which is what the article said) and "This material has no critical field" (which is what the summary said).
Bugrit! Millenium hand and shrimp!
That's really neat and all, but please let me know when they find something that's immune to gravity, as it's essential to a project I'm working on. (I have a deadline.)
Ack - looks like caffeinated_bunsen beat me to the punch. But it bears repeating - this paper certainly says nothing like "this superconductor is immune to magnetism". This material has a very high critical magnetic field, and if they figure out how to improve the connectivity then it might even someday be able to carry a current density of engineering significance. But it certainly is not "immune" to magnetism in any qualitatively different way than any other type-II superconductor out there. Still...it's nice to see that high-temperature superconductivity can be observed outside the cuprate family, and this paper (showing that it also has a high critical magnetic field) should spur some serious R&D work outside the theoretical physics community.
Reasoning is never, like poetry, judged from the outside at all.
I am a condensed-matter physicist but not a superconductor specialist.
The article does not say that the material is immune to magnetism.
The data relevant to this discussion is presented in Fig. 6 in the paper, which is a plot of the upper critical field (the maximum field the material can support and still be superconducting) versus temperature. Look at the traces marked with square markers.
Notice that these curves do not diverge to infinity as the summary would have you believe.
Granted, values in the 50's of Tesla seem pretty big, considering that the ambient magnetic field on Earth is about 0.5 Tesla. But note that other superconductors have critical fields in this same range. The famous high-Tc superconductor YBCO has a critical field of 135 Tesla (ref: http://www.springerlink.com/content/j0128jt30843362u/)
Compared to elemental superconductors, whose critical fields are around 1 Tesla or less, this material does indeed support a lot more magnetic field. But it certainly isn't "immune to magnetism"
Wait, wrong Short Circuit...
Mark Anthony Collins
I read an article in the last year that talked about using liquid hydrogen to cool super conducting transmission lines and also being used as an infrastructure to distribute hydrogen for use in cars, fuel cells, etc...
- 1.5 T is what's used in MRIs (people have died when metallic objects fly around in these fields)
- 16 T will levitate a frog
- 45 T is the strongest magetic field continuously produced in a laboratory.
- 10,000 T is instantly lethal to organic life
Basically we're fine levitating frogs, but probably won't be able to use it as part of an instant-death ray.Crystal Skulls?
Immune to magnetism? Not even immune to fields we can reach!
As mentioned by caffeinated_bunsen above, the upper critical field at 0 K extrapolates to "only" about 60 T; higher values are common in the (now 20 years old) cuprate superconductors. (Actually, the upper critical field is really a poorly defined concept in the cuprates, because it's more of a slow crossover, with remnant superconductivity persisting up to much higher fields than we can produce.)
Also, 60 T is not an inaccessible field by far; several facilities in the world have several pulsed magnets capable of this, with some up to 100 T. More destructive multi-stage, one-shot methods (involving explosives to implode current-carrying coils) can reach 1000 T! These fields require giant capacitor banks, but it's quite possible to produce them in a lab (and not just on a neutron star).
Superconductors that are immune to interference from magnets would get us further towards Bussard Ramjets. There are other hurdles, like the mechanical strength of the magnetic coils themselves. (So the magnetic forces don't wreck them.) Even if we couldn't make practical ramjets, magnetic sails would also benefit, which would make deceleration of interstellar craft almost "free."
http://en.wikipedia.org/wiki/Bussard_ramjet
... "New Supercomputer Found 'Immune To Magnetism'", and for a moment I was wondering how something like that was engineered.
Random Thoughts From A Diseased Mind (Not For Dummies)
It's called a geek. They've been immune to magnetism for years. What? It says superconductor, not supercomputer? I need to lay off the caffeine.
I have made a habit of stating time and again, any time I see someone who quotes Albert Einstein's quote about the weapons that will be used to fight world war 4, of noting that if they're right, then after world war 3 there will be no electricity or anything else to prove that they predicted it, and thus should use their forum sigs more wisely. I suppose then that whenever someone finds a way to fashion this into a motherboard, between that and a solar charger, I am now wrong, so I just want to take this space to apologize to all those I insulted. At least once they make it into a motherboard. If WW3 doesn't happen first. Else, yeah, you're still stupid.
The summary lists the article as being a NATURE preprint, but the link points to arXiv.org, which is tied to Cornell University Library. Isn't NATURE's pre-print service through http://precedings.nature.com/ ?
> 10,000 T is instantly lethal to organic life
I looked at Wikipedia, then I looked at Wikipedia's source because I was curious. That source had normal looking information, then some stuff about EM causing cancer and stuff about magnetic healing because 'DC magnetic fields' were better for you. Or something.
Does anyone know if (and more importantly, WHY) a magnetic field that strong would kill you? Is it supposed to be because water is diamagnetic or something? Or are we going with the explanation from an old Star Trek episode that it's "strong enough to rip the iron from your bloodstream"?
Is this another material looking for a problem?
The knack of flying is learning how to throw yourself at the ground and miss. - HGTTG
Why not use stacks of thin layers of superconducting material instead of wires? Since B ~ N and B ~ I (B := generated magnetic field; N := turns of wire; I := current) you can compensate less turns with more current (which shouldnt be a problem since the cross-sectional area of your layer should be slightly larger than that of an equal layer of wires). And since you're using superconducting material, you won't lose energy through eddy currents (but this might generate unwanted noise/stray fields). Or coat your favourite ductile wire material with a superconductive layer.
A somewhat off-topic digression:
The conventional wisdom on Bussard Ramjets (included in the wikipedia article) is that they reach a terminal velocity due to the drag of collecting the fuel - and asymptotically approach their exhaust velocity. IMHO that's incorrect.
The bug is that the calculation assumes that they must accelerate the collected hydrogen to the velocity of the craft before fusing it, then depend on the fusion energy to re-accelerate it as exhaust.
However, as with the collected air in chemical ramjets, the momentum of the collected material does not need to be discarded. It can be fused on the fly through the ramjet, retaining its original momentum along the flight path (relative to the vessel). Thus the energy of fusion can be applied to accelerating the reaction products toward the rear. None is needed to replace the momentum allegedly lost capturing the fuel.
Now SOME of the axial momentum of the incoming fuel is traded for radial momentum to collect it. But the energy of that "lost" momentum is converted to pressure and temperature, compressing the material like any other gas. There is a drag on the scoop field from this. But when the exhaust expands again after the reaction there is a corresponding thrust against the nozzle field, reconverting the radial expansion of the reaction products to rearward velocity and recovering the "lost" momentum.
If this whole process were lossless there would be no top end to the kenetic energy the ramscoop could accumulate. With less than 100% efficiency in reapplying the compression energy to the mass (both from lost energy and lost mass) there is some drag from collection that is not recovered. (For instance: Mass lost as neutrinos is a non-trivial fraction.) So there may still be a speed limit. But it can be far higher than that calculated by assuming you "stopped" the gas when you "caught" it.
Bantam Dominique roosters crow a four-note song. Once you've heard it as "Happy BIRTHday" you can't NOT hear it that way
- 10,000 T is instantly lethal to organic life
Out of curiosity, what is the rationale for this number (the reference just links to another reference, which has no source)? And what happens at this field intensity?A more important near term result would be a cheap Bussard Polywell fusion system.
A high temperature superconductor that is resistant to high magnetic fields would allow significant efficiency gains and eventually miniaturization.
Who knows in 40 years every new home might have it's own fusion reactor in the basement because of this material.
This country was never a colony. Certain parts of it were colonized by said EU member, but the country built itself through the standard methods of genocide and thievery.
...PUNY HUMANS
...how scientists don't undertsand how superconductors work.
Do we not understand quantum mechanics? Do we not know how the various forces in the universe work?
Given that we know these things, why is it so hard to understand how a superconductor works? I mean there's only so many forces that could be at work here between the atoms in the material.
I just don't get it.
No offense meant to the poster, but what part of this comment deserves +4 insightful?
Some perspecitve: A Magnetar has a magnetic field of 10 GigaTesla. That is a field energy density of 4x10^25 J/m^3. That equals an E/c^2 mass density 80kg/cm^3 or >10^4 that of lead.
Good magnets on earth have a field of 10T.
don't cut it off www.mgmbill.org
The conventional wisdom on Bussard Ramjets (included in the wikipedia article) is that they reach a terminal velocity due to the drag of collecting the fuel - and asymptotically approach their exhaust velocity. IMHO that's incorrect.
The bug is that the calculation assumes that they must accelerate the collected hydrogen to the velocity of the craft before fusing it, then depend on the fusion energy to re-accelerate it as exhaust.
However,[...] The standard design for a Bussard ramjet seems to be to use the field just to collect the hydrogen in the ship, which then is fed to a nuclear rocket inside it, which directs the energy towards the back rather than in every direction. As such, you need to stop it, or close to that.
There are two possibilities around this I can think of:
-The field itself compresses the hydrogen hard enough to fuse. Since the reaction is in free space, it would explode in every direction, rather than be directed so you can harness the assymetry. You'd need to have an Orion-style push plate or a solar sail to get any acceleration out of it.
-The engine is somehow open-ended so that it can still accelerate things backwards without stopping the material.
Even if you could arrange these, both of these suffer from the same problem, IMHO. If you're going at 1/2 C, the material will go too fast for you to able to collect enough quickly enough to fuse it. Standard-style ramjets won't have a problem with it since even if you collect 10% of the material, you're going through getting 10 time more material, which is collected and concentrated. If you're going too fast for your field to fuse the material before it's beyond the field, then none of it will fuse. Similar problems would happen with an open-ended reactor.
It might be just an engineering problem, and I'm not sure how feasible it is. Still, it's different enough that it's not a Bussard ramjet with those changes.
What part of "almost" do you not understand? Compared to lugging along the reaction mass and fuel to brake by firing rockets, a magsail is fantastic!
The field itself compresses the hydrogen hard enough to fuse. Since the reaction is in free space, it would explode in every direction, rather than be directed so you can harness the assymetry. You'd need to have an Orion-style push plate or a solar sail to get any acceleration out of it.
Nope.
Just as you have a big magnetic (or whatever) forward-facing funnel out front to redirect the incoming hydrogen, compressing it into a narrow (fusing) stream, you have a big rear-facing funnel out back (like a giant, invisible, rocket nozzle) to redirect the expansion of the now hotter and expanding stream into a rearward-directed jet.
It's just like most other heat engines: Apply work to compress the gas, add heat, extract (more) work as the hotter gas expands with more pressure than when you compressed it. The forward thrust against your nozzle is more than the rearward thrust against your scoop, even if only by a small percentage. Thus you keep accelerating until the percentage of losses from other issues matches the percentage of gain from the fusion, just as an internal combustion engine can run as long as the mechanical power gained from each cylinderfull of fuel-air mix is greater than the friction losses, even if the power temporarily borrowed from the flywheel to compress it is many times the gain.
Now the issue of the temperature x pressure x time product of the compressed stream is a
Bantam Dominique roosters crow a four-note song. Once you've heard it as "Happy BIRTHday" you can't NOT hear it that way
(oops. Continuing...)
Now the issue of the temperature x pressure x time product of the compressed stream is a separate matter. But AFAIK it's also unsolved for current ramscoop proposals. So I'll wave my hands on that one. B-)
Bantam Dominique roosters crow a four-note song. Once you've heard it as "Happy BIRTHday" you can't NOT hear it that way
IMHO. If you're going at 1/2 C, the material will go too fast for you to able to collect enough quickly enough to fuse it.
Fusion is proportional to the pressure x density x confinement time product. Pressure and density both go up and confinement time goes down with the first power of the speed. So power goes with v*v/v, or also up with the first power. (Material collected also goes up with speed but I think that's already accounted for in density.)
If you get it to produce power at any speed it will produce MORE power if it's going faster. (Which is what you expect, since it would generate no compression and thus no power at all if at rest with respect to the interstellar gas supply.)
Relativistic time and space distortions also work in your favor at very high speeds. They both make it appear to you that you're collecting more fusible material.
Bantam Dominique roosters crow a four-note song. Once you've heard it as "Happy BIRTHday" you can't NOT hear it that way