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I watched that video a few weeks ago.

The main issue is that ITER is built and designed using legacy superconductors. Recent developments, and they're ongoing are allowing the designs to be reengineered.

The new superconductors can work with a much higher magnetic flux. There was something about the efficiency of a reactor increasing with the fourth power of the magnetic flux (B^4). And as I said they're still making improvements to superconductors.

Another idea used is FLiBe salt as a coolant. One of the issues with Fusion reactors is that most metals can't withstand the neutron flux. Using a molten salt blanket solves that problem, along with the idea of changing out the insides periodically.

Nuclear Fusion isn't my thing so I may be off of the mark.

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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. 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.

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.

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

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.

And even if the strong steel beams hold them initially, the bombardment with the neutrons will weaken them. And then... boom.

Damage from high-speed neutrons is deal killer. Periodically replacing neutron-damage magnets is too expensive.

This must be the lecture: https://www.youtube.com/watch?v=KkpqA8yG9T4

I'd really would like to know what the German Wendelstein people would do with those better Superconductors. Can you build a smaller Stellarator?

Professor Whyte said yes - he said that they would use the Stellarator design if it made more sense.

Now that's very interesting. The main thing I've wondered about fusion - given the huge size and expense of the ITER reactor, even if they get power-positive, will they ever be able to build and run reactors cheap enough to be competitive with conventional power production, and keep them running for decades?

ITER is mostly a let's-get-this-thing-started than a economically viable reactor. ITER forced development is areas direct related to the reactor, as magnets and construction techniques.

I think everyone agrees that ITER as a science platform is fantastic.

The first solar-cell or coal-power plant probably wasn't cost-competitive either. ITER is more like a horribly expensive experience, but a worthwhile one in my opinion.