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Comment by XorNot | Hacker News Reader

The ground up physics principles for fusion give you ITER at best. Everytime someone has a brand new concept, they get some promising results and then reach the same problem: we need to build a vacuum chamber 10 meters in diameter to see if it'll produce power. And then you're back to ITER - which is what its exactly trying to do (the internal diameter of ITER is...about that scale).

We know rockets work inside an envelope we can see, it's a matter of how to do it cheaply. What we know, today, is that fusion doesn't work in envelopes much smaller then ITER.

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I thought the arguments for SPARC/ARC were exactly this though, that the approach for ITER is the one we "know" works - but in the time it's taken we now have the ability to make significantly stronger magnets and so should be able to shrink down the overall size dramatically. And size = cost = organisational size = time.

It's a design we've modelled and predicted should work. Since we've never actually built anything close to it, we have no way of knowing whether those models were even close. If ITER shows results that are even close to breakeven you can expect a rush of newer designs using technological advances to shrink scale and improve performance.

Besides, ITER is also meant to help develop experience in handling large plasmas for extended periods of time, that knowledge will transfer to other designs.

ARC actually is a pulsed design, they design against handling plasmas for long periods of time and actually using shorter duration is a net win for efficiency and reliability.

Also, ITER won't demonstrate anything until 2035. By then, several smaller scale designs would have already demonstrated break even.

It seems like there are a dozen or more fusion startups that are pursuing concepts that are much smaller than ITER. I'm no nuclear physicist, but it seems like there might be room for innovation still.

The claim isn't that there is only one way to build fusion reactors, the claim is simply that there is only one well-developed design.

Small prototypes don't mean immediate progress in fusion, the original tokamak was hailed as great progress in 1958 and it was less than a metre across.

Until we have perfect understanding of Magnetohydrodynamics and materials science one simply cannot reliably predict the behaviour of completely new devices.

These prototypes aren't scaled down versions of ITER, the field strength of ARC is of the same magnitude of ITER, it's capable of the same pressures and confinement, only in a much smaller volume.

It's like saying a 5nm CPU design is somehow the same as a 32nm CPU, even if they both had the same die size, even those the 32nm versions had far less transistors.

I never said they were versions of ITER, my point was that the new prototypes themselves need to do most of the upscaling work that's gone into tokamaks. As for Arc, that's simply a tokamak that can't be built yet because the tech isn't ready, not sure what that is supposed to contribute, did you read the rest of this thread?

To summarize:

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Which tech isn't ready? The plasma behavior for that volume was already shown by JET @ 1.5 bar. MIT Alcator C-Mod which achieved a record 2-bar pressure that won't be beaten by ITER for 15 years. Arc also predicts a 2-bar pressure plasma. The difference is, they did it with non-superconducting magnets (copper), and paid a huge price in losses due to resistance. Arc's HTS magnets won't suffer the same problem, will have triple the field strength, and will be structurally stronger.

Arc is doing what JET and Alcator C-Mod did (with a radius very similar to JET), just with a much more power efficient confinement system, so the input power is lower, and the magnetic field is a factor of 2.6 stronger. The basic physics show that stronger fields actually make the plasma more well behaved, not less, so the major variable vs JET (a proven existing tokamak with Q=0.67) that's changing is not likely to lead to surprising results.

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