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Comment by aaronblohowiak | Hacker News Reader

ITER isnt meant to have Q-total > 1 though, it is meant as an experimental platform not energy generation. I wonder if the author has similar thoughts on promise for smaller reactors that take advantage of HTSC magnets.. should they have an easier time achieving breakeven Q-total?

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Her point is that almost all coverage of fusion elides the difference between Q-total and Q-plasma. I didn't know how big the difference was until reading her article and I'm guessing almost no one else does either.

Her point is that the "Q" that has been used to sell ITER leads the public and policy makers to believe it is Q-Total, not Q-Plasma.

And beyond Q-Total is ROI: the ratio of $ in to $ out. An ignited fusion reactor with very high Q could very well still be below economic breakeven.

> should they have an easier time achieving breakeven Q-total?

I believe that’s why they’re being made: Q being a function of both physical size and magnetic field strength, and the new superconductors being useful for increasing the latter so the former can be reduced.

But I have no idea if any of them are currently attempting Q_total > 1 or not: too much hopeful PR for me to know what stage they’re really at.

How could they possibly be attempting Q-total > 1 when they aren’t even near Q-plasma = 1 yet?

If the gain of the system overall is greater than Q-plasma, you’ve invented some other energy source in there somewhere and should throw away your reactor and focus on that thing. :D

I’m not sure what you’re arguing against here. The new fusion startups claim the tech now exists to make compact useful Tokamaks. I’m not a physicist of any kind, so I don’t know what they think their MVPs are. I don’t know, and am not claiming to know, if they’re jumping straight to {Q_total, Q_plasma} > 1 or if they’re going to make a mere Q_plasma > 1, Q_total < 1 “fund-raising only” demo reactor first.

I’m responding to “but I have no idea if any of them are currently attempting Q_total > 1 or not.” My point is that literally nobody is going to set their target on Q-total > 1 without first setting a target of Q-plasma > 1. It would be like wondering if a rocket company was setting their sights on landing on the moon straight away or if they were going to attempt to escape earth’s atmosphere first.

Edit: one might think Q-plasma > 1 is just an internal milestone, not a public goal, but it’s not. Fusion startups are all going to be forced to make a public fuss over Q-plasma > 1 because the amount of funding you need to get from there to Q-total > 1 is MASSIVE and that milestone will be an investor aphrodisiac.

No currently operating device is 'attempting' to achieve Q_total; they are all physics experiments, not simply searching for a magic combination of knobs that will ignite the plasma.

The Europeans are doing quite a bit of preliminary design scoping and engineering for DEMO, a 'demonstration' reactor which is supposed to come after ITER and generate net electricity, but there's not been a site selected, for example. Similarly, Chinese researchers are working on their CFETR, 'Chinese Fusion Engineering Test Reactor'.

Those are all (government funded?) mega-projects.

I’m not talking about that category.

I’m talking about private sector stuff by groups which claim developments in superconductors means they can do it privately for much less, e.g.: https://arstechnica.com/science/2021/09/mit-backed-fusion-st...

I lack the knowledge to tell real projects in this sector from snake oil.

I feel like if this was the 2000s all over again, with ITER making headlines alongside some dubious claims of fusion being around the corner.

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