Are Permanent Magnets the Solution For Delivering Fusion Energy? (phys.org) 42
According to research published in the journal Physical Review Letters, permanent magnets akin to those used on refrigerators could speed the development of fusion energy. Phys.Org reports: In principle, such magnets can greatly simplify the design and production of twisty fusion facilities called stellarators, according to scientists at the U.S. Department of Energy's (DOE) Princeton Plasma Physics Laboratory (PPPL) and the Max Planck Institute for Plasma Physics in Greifswald, Germany. PPPL founder Lyman Spitzer Jr. invented the stellarator in the early 1950s. Most stellarators use a set of complex twisted coils that spiral like stripes on a candy cane to produce magnetic fields that shape and control the plasma that fuels fusion reactions. Refrigerator-like permanent magnets could produce the hard part of these essential fields, the researchers say, allowing simple, non-twisted coils to produce the remaining part in place of the complex coils.
Rare earth magnets have surprising and useful properties. They generate quite powerful fields for the magnets' small size, and these are "hard" fields that are almost unaffected by other fields nearby. These magnets could thus provide what physicists call the "poloidal" part of a spiraling stellarator field, while simple round coils could provide the "toroidal" part that makes up the rest of the field. Permanent magnets are always "on" in sharp contrast to the standard electromagnetic coils that stellarators and tokamaks use. Such coils create magnetic fields when an electric current runs through them -- current that requires power supplies that permanent magnets do not need. Other advantages of the use of permanent magnets to simplify stellarator coils include: Lower cost than hand-crafted electromagnets; Creation of ample space between the simplified coils to facilitate maintenance; Ability to reposition the magnets to create a variety of shapes for the magnetic fields; and Reduced engineering and manufacturing risks. Permanent magnets have disadvantages, too. "You can't turn them off," physicist Per Helander said, which means they can pull in anything they can attract within range. They also produce limited maximum field strength, he said. Nonetheless, such magnets "can be great for creating experiments on the way to a reactor," he added, "and stronger permanent magnets may become available."
Rare earth magnets have surprising and useful properties. They generate quite powerful fields for the magnets' small size, and these are "hard" fields that are almost unaffected by other fields nearby. These magnets could thus provide what physicists call the "poloidal" part of a spiraling stellarator field, while simple round coils could provide the "toroidal" part that makes up the rest of the field. Permanent magnets are always "on" in sharp contrast to the standard electromagnetic coils that stellarators and tokamaks use. Such coils create magnetic fields when an electric current runs through them -- current that requires power supplies that permanent magnets do not need. Other advantages of the use of permanent magnets to simplify stellarator coils include: Lower cost than hand-crafted electromagnets; Creation of ample space between the simplified coils to facilitate maintenance; Ability to reposition the magnets to create a variety of shapes for the magnetic fields; and Reduced engineering and manufacturing risks. Permanent magnets have disadvantages, too. "You can't turn them off," physicist Per Helander said, which means they can pull in anything they can attract within range. They also produce limited maximum field strength, he said. Nonetheless, such magnets "can be great for creating experiments on the way to a reactor," he added, "and stronger permanent magnets may become available."
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Re: No, retard (Score:1)
Perhaps large bursts of natural energy, i.e. lightning strikes, could be harnessed for the creation of strong rare earth permanent magnets. The incredibly high energy of the lightening strike could be captured in a tower and fed down to a very stout high current coil to magnetized the raw metal. I've worked at a motor manufacturer where multi pole magnets are made with high-current-surge coil apparatuses like this.
Not sure if serious ... (Score:5, Funny)
A bit early for April 1 posts isn't it?
Or did I miss something and it turns out that high-energy physicists were somehow unaware of permanent magnets before now.
"You Can't Turn Them Off!"
You don't say?
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And don't rare earth magnets have a curie point of 400C? I believe the inside of a fusion reactor might actually exceed that by a bit.
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The magnets are on the outside of the reactor.
Re: Not sure if serious ... (Score:2)
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Physicists are aware of permanent magnets. They just haven't seriously considered them before because ... they won't work. They are nowhere near strong enough.
Even the summary acknowledges this in the final sentence.
Betteridge's law of headlines [wikipedia.org]
News (Score:2)
If you spin a copper wire around permanent magnets, a wondrous force is created along it's length, and you can generate tiny bits of lightning when the ends are brought together. Scientists are calling this newly discovered force "Lightningicity"
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Betteridge's law aside (Score:5, Informative)
Re:Betteridge's law aside (Score:5, Interesting)
No, because fusion temperature scales with the 4th power of field strength, which ranks as the most sensitive parameter to optimization, even above radius of tokamak.
But the confinement field IS still being produced by big, powerful, superconducting magnets. They just get to be simplified back down to the same sort of simple toroidal-field magnets you'd find in a tokamak.
The permanent magnets would only be supplying the added magnetic components that make the path of the charged particles in the plasma twist around the center of the big donut region, doing the stellarator hack of travelling through both convex field regions (where instabilities tend to spread them out) and concave field regions (where they tend to clump them together), cancelling out much of the plasma instabilities that cause particles to sneak out of the magnetic bottle in a straight tokamak. (Imagine the "donut" of the magnetic bottle made of a bundle of spaghetti in a tokamak, of a twisted rope in a stellarator.
Some strong rare-earth magnets should be quite adequate to add these field tweaks, letting the designers make a simple structure that does the fancy job.
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The permanent magnets would be outside of the containment, the same way that the liquid helium temperature superconducting magnets are, so temperature isn't a problem.
It would be a fantastic simplification if they were strong enough, but they are weaker then superconducting magnets by a large factor.
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Except that the curie point of the powerful Nd magnets is around 85C if I remember correctly.
That ain't very hot compared to fusion temps which they will need to be relatively close too to get the field strength up.
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You are going to have superconducting electromagnets there with their supplies of liquid helium, so it is going to be no problem cooling those permanent magnets too, if that needs to be don.
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I jumped on the same bandwagon as you initially - but then actually RTFA. They are not talking about using permanent magnets for the main field, but instead for field shaping where presumably much smaller fields are needed. That puts the problem out of the range of back-of-the-envelope calculations and into something that needs a real study.
That doesn't mean its right - but it is not as obviously wrong. If it works its not a game-changer, but maybe a nice simplification
Fields are not strong enoough (Score:2)
Superconducting magnets support much higher fields than do any permanent magnets. The machine would need to be enormously larger. (as compared to the already insanely huge ITER).
Almost a trivial additional problem is that permanent magnet materials are fairly radiation sensitive.
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Replying to my own post. I didn't RTFA, and now that I've looked more, they are not trying to generate the main field, but rather to shape it. That is not obviously impossible and might be a good idea. Probably not a game changer, but maybe a cost and complexity reduction. I shouldn't have written so quickly
Am I understanding the article correctly? (Score:4, Interesting)
It seems they are saying that permanent magnets could simplify the design if they were powerful enough. It seems the proposed solution, for actual commercial reactors, would require, as a prerequisite, the discovery of new, more powerful permanent magnets.
What am I missing here? (Score:4, Interesting)
It's not like a bunch of physicists are sitting around after having been granted a few billion dollars for a new fusion reactor and asking: "So... uhh.. guys, do we go with permanent magnets, or electromagents?"
Geezus. Is this posting for real?
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It's not like a bunch of physicists are sitting around after having been granted a few billion dollars for a new fusion reactor and asking: "So... uhh.. guys, do we go with permanent magnets, or electromagents?"
ITER got the billions. This is for stellerator, a variant on the ITER tokamak that tries to get fancy with magnetic field shapes to solve some of the problems of a vanilla tokamak (though its original concept and design predates the tokamak). It also has basically no funding. The largest one built so far is in Germany, the Wendelstein 7-X test reactor, finished in 2014. They spent a year after that just testing the magnets. They're hoping to be able to run it for up to 30 minutes at a stretch next year
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Magnets, how the F do those work? (Score:2)
Rare-earth magnets don't like ionizing radiation (Score:3)
I don't see any mention of this: rare-earth magnets suffer from demagnetization in high-radiation environments. Your design needs to be robust for magnets changing over time. Samarium-cobalt magnets are the most robust type, but I'd like to see some numbers for this application.
Fly it (Score:2)
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Got temporarily banned from a site once, Huff Post if I remember correctly, for a post like that. Apparently they were worried that the terriers might see it, act on the idea, and then they would get the blame.
No! (Score:2)
First, Betteridge, second, the name already has all the information you need RARE earth.
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Rare earth elements aren't actually all that rare, they're just hard to extract.
Part of it, anyway (Score:2)
This project is much closer to commercialization (Score:2)
Refrigerator Fusion (Score:1)
Fusion fridge magnets (Score:2)
It's for cutting edge scientific analysis such as the above, that keeps me coming back here.