11 ms·
Confirmation of the topology of the Wendelstein 7-X stellarator’s magnetic field
- mkj 10y agoIs the strange geometry just one possible arrangement (current best optimisation) or is there something more specific about it? To an outside observer the apparent lack of symmetry etc is surprising.
- chillydawg 10y agoIt has 5 fold symmetry. It's broadly a pentagonal shape (viewed from above) made up of the same piece repeated five times. It's actually rather simple and beautiful (to my eyes). I'd not have been surprised if the model they ran spat out some ridiculous random-looking shape that happens to fit some local minima. As it is, it's a fairly reasonable-looking twisted ribbon like shape.
- drjesusphd 10y agoThe shape has been optimized by simulation. A twisted magnetic field is needed to keep particle orbits confined. Tokamaks generate this twist with a current around a symmetric torus, stellerators do so by relaxing the symmetry.
- hughes 10y agoThis is a very confusing title. 1:100,000 is not a magnitude of a magnetic field. It refers to the approximate deviation from the desired magnetic topology that the stellerator experiment was targeting.
- intransigent 10y agoSo, magnetic fields can be used to confine fusion plasma with "five nines" reliability?
- taneq 10y agoNo, they just generated the fields they wanted to within that accuracy.
- kensai 10y agoAmazing. And remember, this stellarator is our "Plan B". The main effort is in the alternative method, the Tokamak (in ITER).
- threeseed 10y agoAnd Plan C is ARC/SPARC out of MIT which I like because it is taking more of a startup approach and addresses issues such as financial return on investment, maintenance etc. https://www.youtube.com/channel/UCMFsHceLUJNkXMiCMFNnvkA https://www.youtube.com/channel/UCMFsHceLUJNkXMiCMFNnvkA
- andrewflnr 10y agoBetween stellarators working out and these guys, I'd actually put ITER down as plan C, not A.
- mtgx 10y agoIsn't plan A what Lockheed Martin is building? At least they made it sound like they were the closest to real fusion. http://www.lockheedmartin.com/us/products/compact-fusion.html http://www.lockheedmartin.com/us/products/compact-fusion.htm...
- chillydawg 10y agoYeah, but Lockheed could just be running a scam to fleece the US govt out of millions in research grants and tax credits. Obviously it's a huge bet that could pay out $lol if it succeeds, but I suspect it's more of an accounting trick than serious R&D.
- XorNot 10y agoThey're not running a scam, but they don't have the results to be in more then the research curiousity stage. Keep in mind too, the W-7 isn't designed to be net energy positive either whereas ITER is.
- ars 10y agoBit of a summary: This is a stellarator which is the same idea as a tokamak: Confine hydrogen with magnets and get fusion. The magnetic field in a stellarator is crazy complicated, and was impossible to model and design before computers. With computers they were able to design it, but were unsure if they could build it. This is a test showing that yes, they can actually build it. In theory stellarators are simpler to get right than tokamaks, but only if you can actually design, and then make one.
- WheelsAtLarge 10y agoThanks for the summary
- mynewtb 10y agoAny chance for an ELI5 of what a stellarator and tokamak are?
- germinalphrase 10y agoYes - I would appreciate the ELI5
- ars 10y agoSure. If you squish hydrogen atoms together hard enough, and hot enough, they release energy. But it needs to be really really hot - so hot that anything you made it out of would melt. So what do you do? You use a magnet. The magnet squishes the really hot hydrogen without actually touching it. But if you squish one side, the hydrogen will want to go out of the other side. So you have to squish all sides exactly the same amount. It turns out, it's impossible to make a magnet in the shape of a ball that squishes on all sides equally. But, it is possible to make one in the shape of a doughnut! That's a tokamak. They are complicated because you also have to use the hydrogen inside the tokamak to help make the magnet work and keep the hydrogen inside. Another shape that works is a kind of twisted doughnut, this is called a stellarator, if you do that, you don't need to also use the hydrogen inside as a magnet, and this makes it easier. But the twisted shape means it's harder to build because you have to put the magnets in exactly the right place. The name "tokamak" comes from a sentence in Russian describing the machine, and the name "stellarator" comes from a word that means "sun".
- noobermin 10y agoI was at the 2016 APS Department of Plasma Physics Meeting a month or so ago. I work in Laser Plasma, so I have only a surface understanding of the magnetic confinement stuff, but I did attend a keynote by this group, and my impression after the talk was that they were approaching a respectable result but hit a snag. Looks like they couldn't get this out before DPP but fine enough, they can confirm it today, so cheers to them.
- clebio 10y ago> surface understanding plasma physics jokes ftw
- gnarbarian 10y agoHere are two videos that do a great job of conveying the incredible accomplishment of building it. https://www.youtube.com/watch?v=u-fbBRAxJNk https://www.youtube.com/watch?v=u-fbBRAxJNk https://www.youtube.com/watch?v=lyqt6u5_sHA https://www.youtube.com/watch?v=lyqt6u5_sHA
- bjelkeman-again 10y agoFor a beginner, this was good followup material: https://en.wikipedia.org/wiki/Stellarator https://en.wikipedia.org/wiki/Stellarator
- saganus 10y agoHow the hell do you test such a monstrosity? I mean... I know that testing complex software projects is a pain in the ass. But... this? I mean... how do you even begin to plan where all the wires and other elements go and then test that it's a sound design? I'm guessing they do a lot of simulations and such, but what if something fails? how much do you have to backtrack to fix a potential bug? It just boggles the mind. I had no idea these things were so complex. Thanks for the links. Edit: This video explains the elements quite in an understandable way [0] [0] https://www.youtube.com/watch?v=lyqt6u5_sHA https://www.youtube.com/watch?v=lyqt6u5_sHA
- alephnil 10y ago> How the hell do you test such a monstrosity? That is very complex, and a large part of the design process is to make sure it actually is testable. The article actually describes the result of some of the system testing of the device. They have now measured the magnetic field and found that it reproduced what they predicted it should be.
- Animats 10y agoWow. I'd seen renders of the proposed magnet geometry, and it looked like a nightmare to build. They actually built it successfully. It was built by welding curved parts together, not 3D printing the thing in metal. It uses a superconducting magnet, which means having to wind coils from somewhat brittle niobium-titanium alloy. These are strangely-shaped non-planar coils which operate at liquid helium temperatures a few centimeters from 100 million degree plasma. Here's an industrial view of the construction project.[1] Considerable new manufacturing technology had to be developed to build this. One minor component is a diamond window 120mm across and 1.8mm thick, soldered into a stainless steel frame with copper-silver-titanium solder. Cost €370M. Look at the construction pictures and you can see why. I wonder how the Skunk Works fusion project is coming along. They have an even stranger geometry. The only word out of Lockheed is that there's been enough progress to justify spending more of Lockheed's money on the project. [1] https://www.ipp.mpg.de/987655/w7x_and_industry_en.pdf https://www.ipp.mpg.de/987655/w7x_and_industry_en.pdf
- 2sk21 10y agoThe attached PDF is wonderful. Is there any other cluster of companies in the world capable of such high-precision mechanical and electrical engineering outside of northern Europe?
- deleted 10y ago[deleted]
- tsomctl 10y agoIf you like the pdf, you might like this tour of the shop that makes a lot of the stuff for Lawrence Livermore labs: https://www.youtube.com/watch?v=FmmNRaKpBTI https://www.youtube.com/watch?v=FmmNRaKpBTI
- criminalpatto 10y agoIf you read carefully 2 of the suppliers are Italian : CLP for the central ring and Ansaldo for the superconductiong magnets.
- m_mueller 10y ago
- mozumder 10y agoHow small can these stellarators get? Is there a necessary minimum strength magnetic field that basically creates a minimum size for a stellarator?
- raverbashing 10y agoI'd say the smaller the Stellerator is, the stronger the magnetic fields have to be, as the curve radiuses are smaller So there's probably an ideal size
- krashnburn200 10y agomy math suggests something approximating the size of a star could achieve fusion by using only gravity for containment. I wouldn't want to stand too close to that sucker though.
- pavlov 10y agoIf someone had built such an object, say 10,000 light years away, what would it look like to us?
- krashnburn200 10y agonothing for 10,000 years - however long ago they built it.
- deleted 10y ago[deleted]
- k__ 10y agobut aren't stars varying extremely in size?
- wolrah 10y ago> but aren't stars varying extremely in size? Woosh. A star is a fusion reactor using only gravity for containment.
- foota 10y agoAnyone know why you can't just build a really long solenoid?
- wtallis 10y agoThat would allow you to keep a quantity of plasma confined for a longer period of time than a short solenoid, but doesn't help you keep the plasma density/pressure up high enough for sustained fusion.
- Ygg2 10y agoSimple. A solenoid isn't closed surface. It can't even hold plasma together.
- kriro 10y agoFirst project in a while where I feel my tax money is used well (my guess is the overall cost will end up being around 1.5 billion). The engineering simply makes my jaw drop...sick achievement, congratulations to everyone involved. Surprised that it isn't pushed more in the media here. I think it's really hard to communicate the achievement to the masses but this needs to be on the news way more than it is (and presented better...somehow)
- owenversteeg 10y agoELI5 explanation: Because of something called the "hairy ball theorem" [0], which says you can't comb hairy balls (but you can comb hairy donuts), scientists are making a hairy, combed, billion-dollar metal donut [1] to squish hydrogen atoms evenly on all sides. Once you turn on the machine, the squished hydrogen atoms release energy! This news today is saying that the hairy, combed, billion-dollar metal donut is the right shape, which is very important because nobody ever made a donut like this before, and if it was the wrong shape you couldn't comb it and that means the hydrogen would escape and you couldn't make any energy. [0] https://en.wikipedia.org/wiki/Hairy_ball_theorem https://en.wikipedia.org/wiki/Hairy_ball_theorem [1] http://www.sciencemag.org/news/2015/10/bizarre-reactor-might-save-nuclear-fusion http://www.sciencemag.org/news/2015/10/bizarre-reactor-might...
- dom0 10y agoAn important thing about the 7-X is that it's not about the fusion (squishing), because fusion is fundamentally a very simple process. It's all about the combing (plasma physics), which is very difficult and the reason we don't have squishing-plants yet.
- wolrah 10y ago> fusion is fundamentally a very simple process. For anyone reading who don't get just how simple it is, there are literally hundreds and possibly thousands of people who have built their own DIY fusion reactors at home. Many high schoolers, some of them as young as age 14. Fusion is really easy by scientific standards.
- sdfjkl 10y agoStellarator is a beautiful word. I think it's my word of the year. stellarator |ˈstɛləreɪtə| noun - Physics a toroidal apparatus for producing controlled fusion reactions in hot plasma, where all the controlling magnetic fields inside it are produced by external windings. ORIGIN 1950s: from stellar (with reference to the fusion processes in stars), on the pattern of generator.
- visarga 10y agoIs it true that this reactor doesn't use the latest REBCO superconductors? I watched a talk where they claim they can make reactors 10x smaller now, because they increased the strength of the magnetic field (can go up to 10-20T, instead of 3T). And the superconducting tape is cheap, much more flexible and only needs to be cooled to 100K instead of 4K. If that's true and I'm not mistaken, the MIT ARC reactor would be much better posed to win the race than Wendelstein 7-X, especially that W7X doesn't aim to generate surplus energy. A commenter above was wondering at the expensive diamond window they had to use. This project is going to be too expensive and with dated technology. We could do it cheaper now.
- buster 10y agoThe projects goal is not to build a reactor but to study plasma physics. I'd guess the diamond window is surely industrial diamonds. Fun fact as well: There are inner plates for shielding which are screwed into place. The question is: So you have a shield to protect from very high temperatures but also a screw on the same side. How do you protect the screw? You put a diamond coating over it. :) Also, of course we could do it cheaper now. The project began around 20 years ago and had much luck, because there were many occassions were the techhnology needed to build the Wendelstein was just invented. Source: A german 2h30m podcast with the project lead: https://alternativlos.org/36/ https://alternativlos.org/36/ Extremely interesting!
- Quanttek 10y agoThey started 2003 with the construction. Of course it can be built cheaper and more efficient know, but in 10 years you could again write the same comment about dated technology and cost. In that sense, the project is using up-to-date technology as there is no other similar stellarator running with newer technology. > This project is going to You seem to imply it's still in construction. It's finished already, in fact they finished testing it a year ago.
- mioelnir 10y agoThe design for ITER was finalized in 2001, amended in 2007. Construction for W7-X started 2003. W7-X is now built, fully functional and operational. At several points during its construction, the construction process for its required parts had to be invented first. That's 15+ years of research, breakthroughs and inventions in plasma confinement physics and engineering that have had to happen first. As a noncommercial research reactor, W7-X will continue to be useful for many years to come. For material testing alone I would imagine access to reactor capable of producing a stable, continuous fusion reaction is invaluable. The ARC is a design proposal from 2015. As such they have access and can utilize all the achievements, results and processes from W7-X, ITER and other material science advances of the last 15 years. If their proposal was not better than already built specimens, it would be a bad proposal. To declare it a race against the research foundation they built upon seems ignorant at best. In 10-20 years, when the ARC is built, a new design proposal will emerge, based on even newer advances in material science and the lessons learned from building the ARC. And it again will be better than the then current, assembled reactors. That is how it is supposed to be.
- i2amsam 10y agoWhat is an optimistic timeline from here? When could this be energy positive / used commercially?
- asmithmd1 10y agoThe same as it has been for the past 50 years - about 10 years before commercial use.
- zachrose 10y agoPresumably each estimate is made with fewer unknown unknowns and thus higher real chances of success?
- tqkxzugoaupvwqr 10y agoI read they hope to have an energy net-positive machine in 2035. Or ~20 years from now.
- twic 10y ago> In a stellarator, nested toroidal magnetic surfaces are created from external magnetic coils What does that mean? What is a 'magnetic surface'? > Each magnetic field line meanders around on its magnetic surface; it never leaves it. In general, if one follows a field line from one point on a magnetic surface, one never comes back to the same exact location. Instead, one covers the surface, coming infinitely close to any point of the surface. Does 'magnetic surface' just mean this, the manifold generated by following a field line? In that case, is it really meaningful to call these 'nested'? If what they're saying is that at any point in the field, following the field will trace out a surface, then there aren't actually discrete surfaces here, and it's not entirely meaningful to call them nested. It's like talking about the contour lines on a hill being nested, when what you really mean is that the hill has a smooth gradient.
- drjesusphd 10y agoA "magnetic" (or "flux") surface is one in which particle orbits remain confined. The only way they move from surface to surface is via colliding with other particles, or by being carried away by turbulent fields. I've never heard that "nested" need only refer to a finite number. It's a way to illustrate, with words, how such surfaces relate to a 3d torus. I don't see anything wrong with this.
- vilhelm_s 10y agoThe nestedness is about the topology of the surfaces, it means that most of the surfaces are concentric around a single point. The alternative is that there are lots of little islands, so if you plot the 2d cross section there will be rings that are next to each other, instead of one being inside the other. In the extreme case you can get "stochastic" patterns, where there are infinitely many islands in a fractal pattern. See the e.g. figures here: http://iopscience.iop.org/article/10.1088/1367-2630/15/1/013061 http://iopscience.iop.org/article/10.1088/1367-2630/15/1/013... https://en.wikipedia.org/wiki/File:Stellarator_magnetic_field.png https://en.wikipedia.org/wiki/File:Stellarator_magnetic_fiel... In the hill metaphor, saying that the surfaces are nested corresponds to there being a single of peak of the hill.
- dghughes 10y agoI love the technology but I find it amusing to get free energy from fusion we just have to build the most complex energy hogging device ever made.
- wolrah 10y agoThink about it like a supercharger on a car. They consume power to do their job, but they gain you more than they consume so the net result is more power delivered to the crankshaft. A Top Fuel dragster's supercharger takes around 600 horsepower to drive at full bore, but that enables an engine that's loosely derived from (read: shares core dimensions with) a ~350HP production car to produce more power than a freight train. Sometimes you've got to spend power to make power.
- clebio 10y agoWhat is the process to generate the physical design for this (or for the Tokamak)? Is it a sort of reverse-statics equation solver, where you define the objective (confined field lines, etc.)? There has to be several layers of solving involved, though, since you first determine the forces needed, and then determine the physical hardware needed to create those forces (as well as other systems like material-inlet). I imagine the article and its citations actually contain this information, but might take a while to read through.
- ChuckMcM 10y agoNicely done! To me at the W7-X is at least as impressive as the LHC. I particularly like the ways they measure the magnetic topology by shooting electron beams through a neutral gas. That had me wondering if you could build a 3-D vector display that way. Sort your plasma lamp but with figures inside rather than randomness. Can't wait for them to run plasma through it.
- crispyambulance 10y agoIt all looks very impressive, but why all the funky curves? I thought the idea is to create a magnetic field to contain a plasma. Could that not be done with a torus of circular cross-section? Instead we see a very complex undulating torus, what's the reason for that?
- luca_ing 10y agoA simple toroidal magnet creates a complicated field, while this complicated magnet creates a much simpler and more benign field. AFAIK, in Tokamaks you need to permanently increase the plasma current to keep it stable, which puts an upper bound on the time you can sustain the plasma (you can't increase the current forever). In a Stellarator, by contrast, you can keep the current constant, and thus have plasma durations measured in hours instead of minutes.
- npiazza83 10y agoWhen you use a true doughnut stuff drifts toward the outside of the doughnut. You have to up the current constantly to keep it from drifting toward the outside of the doughnut. If you make a doughnut twizzler it doesn't happen.