Ray Osborne and colleagues at Argonne National Laboratories reported in the July 2nd PRL that electrons zipping past boron atoms in MgB2 quite easily "pluck" the crystal lattice, like a guitar string. The resulting vibration allows two electrons to form a so-called Cooper pair, which then travels resistance-free through the material. Another account in today's PRL from Jeff Lynn and Taner Yildirim at the National Institute of Standards and Technology and their colleagues confirms the earlier work. They further show just how perfectly coupled the lattice vibration is to the conducting electrons. The timing is so perfect, in fact, that the scientists say it will be hard to tweak the material to raise its superconducting temperature any higher.
That is bad because MgB made with B11 is a prime prospect for a superconductor with high neutron resistance.
And here is a recent one on iron based superconductors:
On the other hand, the spin fluctuations that could glue together cuprate electrons might not be enough for those in the iron-based materials. Instead orbital fluctuations—or variations in the location of electrons around atoms—might also prove crucial, Haule speculates. In essence, the iron-based materials give more freedom to electrons than cuprates do when it comes to how electrons circle around atoms.
Orbital fluctuations might play important roles in other unconventional superconductors as well, such as ones based on uranium or cobalt, which operate closer to absolute zero, Haule conjectures. Because the iron-based superconductors work at higher temperatures, such fluctuations may be easier to research.
Besides illuminating the theoretical underpinnings of superconductivity, the discovery “makes us ask if there are other high-temperature superconductors we haven’t found yet in unexpected places and if there are even higher temperatures these can work at,” remarks theoretical physicist David Pines of the University of California, Davis, who is also founding director of the Institute for Complex Adaptive Matter. In trying to boost the critical temperature, experiments should focus not only on swapping in other elements but also on layering the compounds. That should improve them just as it does for cuprate superconductors, Haule thinks.
So far the highest recorded SC field is 100 T. And the highest SC temp. (not in bulk material) is around 180K. Of course not in the same material.
Interesting times.
Engineering is the art of making what you want from what you can get at a profit.
The recent synthesis of the superconductor LaFeAsO0.89F0.11 with transition temperature T c approximately 26 K (refs 1–4) has been quickly followed by reports of even higher transition temperatures in related compounds: 41 K in CeFeAsO0.84F0.16 (ref. 5), 43 K in SmFeAsO0.9F0.1 (ref. 6), and 52 K in NdFeAsO0.89F0.11 and PrFeAsO0.89F0.11 (refs 7, 8). These discoveries have generated much interest9, 10 in the mechanisms and manifestations of unconventional superconductivity in the family of doped quaternary layered oxypnictides LnOTMPn (Ln: La, Pr, Ce, Sm; TM: Mn, Fe, Co, Ni; Pn: P, As), because many features of these materials set them apart from other known superconductors. Here we report resistance measurements of LaFeAsO0.89F0.11 at high magnetic fields, up to 45 T, that show a remarkable enhancement of the upper critical field B c2 compared to values expected from the slopes dB c2/dT approximately 2 T K-1 near T c, particularly at low temperatures where the deduced B c2(0) approximately 63–65 T exceeds the paramagnetic limit. We argue that oxypnictides represent a new class of high-field superconductors with B c2 values surpassing those of Nb3Sn, MgB2 and the Chevrel phases, and perhaps exceeding the 100 T magnetic field benchmark of the high-T c copper oxides.
Obviously if they remain superconducting they are not blowing apart.
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That may impossible to achieve given the minimum size to accommodate the heat loads - but it does mean a possible reduction in size for a given power out.
1 Mw ~ 1,000 hp. So trucks powered by fusion reactors may be in the cards. If the radiation issues can be worked out.
At the very least it may mean lower losses for an operating reactor. Or higher temperature operation at a given field strength. Since maximum field goes up as the temperature goes down.
Engineering is the art of making what you want from what you can get at a profit.
Munchausen wrote:In what way may this affect fusion technology?
Theory has power scaling with B^4 X R^3. Most folks think along the lines of B scaling almost directly with R, which for similar techmologies may be true. And given that, P scales with R^7 which is what most folk talk about. But it is really B^4.
The WB7 was about .3T if memory serves. Thus a 100T unit of the same size would be about 333^4 ~ 10^10 as powerful at the same size. Of course, there may be no way to contain that power...
What about the conventional approaches, the tokamak etc? Will they gain from stronger magnet fields? If so, how much?
In principle, yes. There have been a number of detailed tokamak reactor studies, including sensitivity analyses. Surprisingly, the economics are hardly changed by the assumption that the critical field of the superconductors can be significantly raised. There are too many other constraints that also enter in, such as the mechanics of containing the magnetic forces and the thermal loading on the first wall.
KitemanSA wrote:The WB7 was about .3T if memory serves. Thus a 100T unit of the same size would be about 333^4 ~ 10^10 as powerful at the same size. Of course, there may be no way to contain that power...
I dunno. Instead of 2 neutrons, we'd have 2*10^10 neutrons? 2 mJ? I think we could handle it.
KitemanSA wrote:The WB7 was about .3T if memory serves. Thus a 100T unit of the same size would be about 333^4 ~ 10^10 as powerful at the same size. Of course, there may be no way to contain that power...
I dunno. Instead of 2 neutrons, we'd have 2*10^10 neutrons? 2 mJ? I think we could handle it. :wink:
Nice Art. But I think given the detection efficiency, included angle, etc each detected neutron is worth 3,000 produced neutrons. So you are up to 6 J in 1/4 mS. That would be 24,000 watts. Still not overwhelming. But a step in the right direction. You go up to 1 m diam coils and that puts you up around 860,000 W. A step up to 3 m coils and you are at 23 MW. Assuming you can keep the field constant while increasing the coil diameter. Which is not a given.
Of course the vacuum chamber might need a tad of stiffening to contain the forces generated by the opposing fields.
And then there is the small question of: will it work steady state. So a point or two in your favor.
Engineering is the art of making what you want from what you can get at a profit.
KitemanSA wrote:The WB7 was about .3T if memory serves. Thus a 100T unit of the same size would be about 333^4 ~ 10^10 as powerful at the same size. Of course, there may be no way to contain that power...
I dunno. Instead of 2 neutrons, we'd have 2*10^10 neutrons? 2 mJ? I think we could handle it.
Nice Art. But I think given the detection efficiency, included angle, etc each detected neutron is worth 3,000 produced neutrons. So you are up to 6 J in 1/4 mS. That would be 24,000 watts.
MSimon,
Your count results in ~24M neu/sec. I thought the reporst was ~200M neu/sec. And whereas I admit that 200kW (vice your 24kW) should be easily withstandable, it may still be a real handy size to have around. What am I saying! Even a 24kW machine would be real handy!
I guess the question is, would that size produce net power?
Would pumping up the B field (regardless of the tech used) be a cheaper way of testing scaling vs building a bigger (larger radius) prototype? I mean, couldn't EMC2 either crank up the current on their existing coils or retrofit WB7 with more powerful coils?
Or is B field scaling a given, and R scaling what's in question?
Art Carlson wrote:
I dunno. Instead of 2 neutrons, we'd have 2*10^10 neutrons? 2 mJ? I think we could handle it. :wink:
Nice Art. But I think given the detection efficiency, included angle, etc each detected neutron is worth 3,000 produced neutrons. So you are up to 6 J in 1/4 mS. That would be 24,000 watts.
MSimon,
Your count results in ~24M neu/sec. I thought the reporst was ~200M neu/sec. And whereas I admit that 200kW (vice your 24kW) should be easily withstandable, it may still be a real handy size to have around. What am I saying! Even a 24kW machine would be real handy!
I guess the question is, would that size produce net power?
TBD
Engineering is the art of making what you want from what you can get at a profit.
