this post was submitted on 21 Dec 2023
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Tokamaks also use superconducting magnets, there's really no feasible way to get the necessary field strengths without superconductivity. What makes the two approaches different is that ions want to follow magnetic lines naturally in a spiral which Stellerators lean into and allow (hence the lovecraftian geometry) while Tokamaks try to make them fly straight by inducing a current into the plasma creating a secondary magnetic field, creating turbulence which then has to be brought under control.
The net effect on plasma stability is that with a small Tokamak you're balancing a column of three tennis balls, when you make it bigger you get additional balls to balance. With Stellerators you're balancing a tennis ball in a salad bowl.
The reason early research favoured Tokamaks is because people thought designing the coil and field geometries necessary for Stellerators wouldn't ever work out but then Supercomputers came along (Wendelstein 7-X was computed on a Cray) and, well, as said, the real thing behaves exactly as computed. A thing Tokamaks can only dream of with all their tennis balls.
That's a great point; manufacturing is much better than anticipated even 20 years ago.
I mean that the startup uses high-temperature superconductors and hence uses even less energy for their cooling. Wendelstein 7-X uses "normal" superconductors, and hence requires more energy for that. And a tokamak uses an order of magnitude or so more energy for the magnetic field, than a stellarator does.
But yeah, no idea how much more energy a higher power tokamak magnet picks up from the reaction chamber compared to a lower powered stellarator magnet. But surely the less cool high-temperature superconductors are more tolerant to this than the "normal" ones, since they have more temperature tolerance to work with. Hence, for building a reactor that generates a gigawatt or so of heat, this approach seems really the best that we have now.
Must've missed that "high temperature" before superconductor when reading. Wendelstein 7-X uses Niob-Titanium, very much not high temperature at 10K but as I understand it's the standard for applications because metals, much unlike ceramics, aren't a bugger to deal with. If there's some suitable new materials (it's been 23 years since W-7X started getting built) I doubt they'll use it unless they know it won't be an issue, just not the right thing to bet the project on. Looking at Wikipedia things >77K are still either ceramics or need >150GPa which is insane for an industrial application. Or, wait... yep there's people who use "high temperature" to mean things other that "can be cooled with nitrogen". That might be it, 20K can be done with hydrogen.
Yeah, I have listened to an interview with one of the people working at Wendelstein, and they said that the startup uses "high-temperature superconductors". They didn't go into any detail though, so no idea what exactly they meant.