3 ms·

I'm finding it difficult to Google how efficiency scales with magnetic flux. I've ended up at a thirty five page pdf https://arxiv.org/pdf/1409.3540 https://arx

I'm finding it difficult to Google how efficiency scales with magnetic flux. I've ended up at a thirty five page pdf https://arxiv.org/pdf/1409.3540 https://arxiv.org/pdf/1409.3540. Equation 1 on page 5 states the fourth power dependency. So using REBCO magnets, instead of Niobium-Tin, to get twice the magnetic field looks like a really big deal. Page 6 adds a twist to the story. "For REBCO superconductors operating far below their critical temperatures, the toroidal field is generally limited by mechancical stress rather than the critical current density, which typically limits standard Nb3Sn." So further increases in magnetic field might be waiting on advances in mechanical engineering design, not on better superconductors.

motoboi 10y ago
Really big challenge keeping the magnets from flying apart. They exert absurd forces on each other.
- sgt101 10y ago
  Prof. Whyte thinks that they have that by making really interesting stainless steel coiled tape stuff. I really lost the plot at this point in the presentation and did not understand how it would work, but then he passed round some samples (which could have been anything at all to be fair) so I became convinced that the stainless steal coiled tape approach to fabrication is real and practical. I think his idea is to make the magnets now, quickly, and use them for things like magnetic resonance scanners. I think that will prove the technology which he then intends to scale to a reactor; and several Ph.D folks are busily designing said reactors.
- acqq 10y ago
  And even if the strong steel beams hold them initially, the bombardment with the neutrons will weaken them. And then... boom.
  - wolfv 10y ago
    Damage from high-speed neutrons is deal killer. Periodically replacing neutron-damage magnets is too expensive.
zeristor 10y ago
Another key thing I didn't mention was that at higher magnetic fields they no longer need to worry about plasma instabilities. I believe quite a lot of work had gone into how to managing instabilities. From the video the more powerful superconductors are supposed to reduced those issues. Although a Phyics graduate I'm not an expert in nuclear fusion. They also mentioned that the "magnetic pressure" is the equivalent of 5000 atmospheres, I think I have an idea what they mean. Taking questions someone asks about modes of failure; however catastrophic structural failure wasn't one of them. Not a huge deal since there's scant amount of fusion fuel.

motoboi 10y ago

Really big challenge keeping the magnets from flying apart. They exert absurd forces on each other.

sgt101 10y ago
Prof. Whyte thinks that they have that by making really interesting stainless steel coiled tape stuff. I really lost the plot at this point in the presentation and did not understand how it would work, but then he passed round some samples (which could have been anything at all to be fair) so I became convinced that the stainless steal coiled tape approach to fabrication is real and practical. I think his idea is to make the magnets now, quickly, and use them for things like magnetic resonance scanners. I think that will prove the technology which he then intends to scale to a reactor; and several Ph.D folks are busily designing said reactors.
acqq 10y ago
And even if the strong steel beams hold them initially, the bombardment with the neutrons will weaken them. And then... boom.
- wolfv 10y ago
  Damage from high-speed neutrons is deal killer. Periodically replacing neutron-damage magnets is too expensive.

zeristor 10y ago

Another key thing I didn't mention was that at higher magnetic fields they no longer need to worry about plasma instabilities. I believe quite a lot of work had gone into how to managing instabilities. From the video the more powerful superconductors are supposed to reduced those issues. Although a Phyics graduate I'm not an expert in nuclear fusion. They also mentioned that the "magnetic pressure" is the equivalent of 5000 atmospheres, I think I have an idea what they mean. Taking questions someone asks about modes of failure; however catastrophic structural failure wasn't one of them. Not a huge deal since there's scant amount of fusion fuel.