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Comment by manholio | Hacker News Reader

> two of them could have held down the Space Shuttle when it was trying to launch. To keep the reactor from flying apart, they needed 38

And all that for a reactor that was unable to break even in energy terms, let alone ignite and break even economically.

It perfectly illustrates the folly of magnetic confinement: to hold the plasma you need fields so strong and equipment so massive and expensive that the capital expenses get out of control, fully negating any advantage fusion might have over fission. We already know how to make capital intensive energy - the fueling costs are negligible for a fission reactor, yet those largely failed in the market. An even more expensive and capital intensive solution is dead in the water for economic reasons regardless of any theoretical merits.

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Mechanical strain has never been anywhere near a limiting factor on the engineering of MCF machines.

I never said it was. But a device that needs multiple square feet of high tensile steel to hold together will have immense costs because it also includes gigantic superconducting magnets, vats of cryo-coolant and myriad of custom, unique parts made of exotic materials for exorbitant money.

The billion price tags of tokamak experiments is not a scientific oddity, it's a fundamental economic issue with the approach that will carry on to any production plant, that as far as we can conjuncture will need to be even larger and more expensive.

Nonsense. That's all gravy. The cost difference between experiments and reactors is scale. ITER is a good example to point to. If reactors needed to be the size of ITER mankind could never deploy them at scale because we simply don't have the resources. If ITER was 5x smaller: it's a different story.

> mankind could never deploy them at scale because we simply don't have the resources.

I don't understand what your objection exactly is. That's just a way to rephrase my statement: magnetic confinement, as it stands, is too capital intensive to ever break even financially, regardless of the experimental success ITER/DEMO might have.

I agree if confinement field tops out at 12 T on coil / 6 T on axis. Double it and the story looks very different.

Some light reading on this:

https://www.cambridge.org/core/journals/journal-of-plasma-ph...

Since ITER's volumetric power density is 400x worse than an existing commercial PWR's reactor (+ its pressure vessel), we'd need quite a bit more than a 5x reduction in volume. Even a 5x reduction in linear dimensions (likely impossible at the same power output, due to wall loading 25x higher) may not be enough.

With high temperature superconductors, mechanical strain is in fact now the limiting factor, at least for the magnets.

I must have missed the paper highlighting this fact. Could you share it?

If you look at the 2014 ARC paper, you will discover that 60% of the mass of the reactor is the stainless steel structure for resisting the JxB forces on the magnets.

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