What are all the valves and ports and things in the metal outside of the stellarator in the lead illustration?
Revamped German stellarator should run longer, hotter and compete with tokamaks
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Re: Revamped German stellarator should run longer, hotter and compete with tokamaks
#32Forgive my ignorance; what with all the effort made to isolate the exceedingly hot plasma from connecting with any surface, what are the plans to extract the heat in order to generate power?
By capturing neutrons (which, not being charged, escape the magnetic confinement continuously as the reaction goes on) with a moderator blanket which is then cooled with water/steam. How to keep the blanket from quickly degrading and becoming nuclear waste seems to be an open problem (not too different from what goes on in fission reactors though) https://en.wikipedia.org/wiki/Fusion_power#Energy_capture
> How to keep the blanket from quickly degrading and becoming nuclear waste seems to be an open problem
Not really. Most reactors plan to also use the neutrons to breed the tritium fuel for the reactor, so the blanket would consist of liquid metallic lithium. The only products from neutrons reacting with lithium nucleii (either 6 or 7) are He-4 and tritium.
The open problem is how to safely maintain the reactor-facing wall of the lithium blanket. It gets bombarded by a lot of neutrons, yet needs to contain the hot lithium. It helps that the lithium can be unpressurized, but it's still a problem, because molten metallic lithium is not fun to have leak into anywhere.
The plan of the ARC guys appears to be to design the reactor so that the lithium vessel is easy to remove and swap for a new one, and just use steel for the vessel. The downside of this is that it's going to result in a lot of low-activity waste -- actually probably quite a bit more than what fission plants produce. There are other approaches, including using a material that doesn't really get activated by neutrons, and which is maintained above it's annealing temperature so embrittlement caused by dislocations is repaired as it happens. The downside of this is that materials above their annealing temperatures can be kind of soft.
Re: Revamped German stellarator should run longer, hotter and compete with tokamaks
#33What are all the valves and ports and things in the metal outside of the stellarator in the lead illustration?
Heating and diagnostics.
https://www.researchgate.net/figure/Port-allocation-of-the-W...
There's a chapter on W7-X diagnostics in this DOI (check sci-hub). It doesn't include a comprehensive list of diagnostics or their port assignments, but it was the best I found at a glance.
10.1007/978-1-4613-0369-5_76
Re: Revamped German stellarator should run longer, hotter and compete with tokamaks
#34https://www.energy.gov/science/doe-explainsstellarators A stellarator is a machine that uses magnetic fields to confine plasma in the shape of a donut, called a torus. Over tokamaks, the other main technology that scientists are exploring for fusion power, stellarators require less injected power to sustain the plasma, have greater design flexibility, and allow for simplification of some aspects of plasma control. Ho…
Stellerators aren't really in a torus, they are in a weird fractally twisted torus, sort of like a many-twisted Mobius strip. You really need to see a picture to understand.
Re: Revamped German stellarator should run longer, hotter and compete with tokamaks
#35Forgive my ignorance; what with all the effort made to isolate the exceedingly hot plasma from connecting with any surface, what are the plans to extract the heat in order to generate power?
I'm not sure, but there's a thing called the 'Divertor' in some designs, it's said to be for removing inpurities, but some things talk about it being used for removing heat as well: https://www.iter.org/mach/Divertor
I was going to make a comment about divertors. W7-X has 10 strike points and an island divertor. It's pretty wild physics.
Re: Revamped German stellarator should run longer, hotter and compete with tokamaks
#36Just like COVID helped the mRNA/CRISPR technology evolve and come faster and closer to us, with the potential for many more usages in various diseases, I hope that the ongoing/coming energy crisis will help all nuclear fusion technologies tokamak/stellarator become real. We’re still a few years away from having them in actual power plants and a few decades away from solving our energy problems for every, but I hope w…
"our need will be the real creator" - Plato
Re: Revamped German stellarator should run longer, hotter and compete with tokamaks
#37What are all the valves and ports and things in the metal outside of the stellarator in the lead illustration?
Heating and diagnostics. https://www.researchgate.net/figure/Port-allocation-of-the-W... There's a chapter on W7-X diagnostics in this DOI (check sci-hub). It doesn't include a comprehensive list of diagnostics or their port assignments, but it was the best I found at a glance. 10.1007/978-1-4613-0369-5_76
At first I thought they lacked symmetry. Now I see they don’t, it’s just pretty convoluted
Re: Revamped German stellarator should run longer, hotter and compete with tokamaks
#38Earlier quoted context omitted.
Heating and diagnostics. https://www.researchgate.net/figure/Port-allocation-of-the-W... There's a chapter on W7-X diagnostics in this DOI (check sci-hub). It doesn't include a comprehensive list of diagnostics or their port assignments, but it was the best I found at a glance. 10.1007/978-1-4613-0369-5_76
At first I thought they lacked symmetry. Now I see they don’t, it’s just pretty convoluted
W7-X has 5 periods and each period is a mirrored half period, so really it's one segment repeated 10 times. This pattern is common to symmetric stellarators.
Re: Revamped German stellarator should run longer, hotter and compete with tokamaks
#39Earlier quoted context omitted.
> And it would face the same showstoppingly bad volumetric power density as tokamaks, because of limits on that energy flow through the surface of the reactor. I do think it is worth persevering though. The future of energy is Solar/Wind but Fusion should not be ignored. It is one of Nature's fundamental processes. Mastering fusion could turn out to be useful in ways we cannot possibly fathom at the moment right now.
I agree. If we were able to eventually miniaturise fusion reactors, they would be incredible for space flight. Back on Earth, if they could be made safe enough, maybe we could even use them to run container ships?
With all the fast neutrons emanating from a fusion reactor (and the heavy confinement that it requires) I don't think a container ship would be a safe enough environment (threat of disaster at sea, constantly jostling which might affect plasma stability etc.).
But yes, there is a potential for a lot of space applications and other things we haven't thought of yet.
Re: Revamped German stellarator should run longer, hotter and compete with tokamaks
#40This has to be the most opaque title I’ve ever seen on Hacker News. For anyone wondering, this is about a potential development in cold fusion reactors.
Others are pointing out that this is (very) hot fusion. But I'd just say that if you know the first thing about fusion, the title is actually very simple, ie, stellarators and tokamaks are competing designs for magnetic confinement fusion. Of course, no one is born knowing anything about nuclear physics, and it's not really a casual subject of conversation, so there might be a lesson here that people could take about…
And if you know nothing about fusion, the title seems to be crafted of made up words.
But if you take one glance at the comments, it becomes clear. So I guess the title was sufficient to pique my interest, which, after all, is the purpose of a title.