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Comment by kirrent | Hacker News Reader

You're right about better superconductors leading to more compact and cheaper reactor designs, but many, if not most, of those designs are still tokamaks. To say that the bleeding edge has moved beyond tokamaks is just wrong.

To take your example of Wendelstein 7-X, the only sources I can find give an expected Q factor of 0.1. JET was getting 0.75 ages ago. ITER will hopefully hit 10. While I'm excited about stellarators because they're very interesting to research, they probably won't be catching up to tokamaks any time soon.

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>ITER will hopefully hit 10.

As a layman, is it right to think that this would mean viable fusion has arrived at that point? I mean, 10x energy out/in is a victory, no? Is there another factor that stops ITER from being immediately used and replicated for energy generation?

Well, DEMO, the demonstration power station to follow ITER is estimated to have a Q of 25 and output of 2GW. Whether that's viable will then be less about the physics and more about the cost that they can get subsequent designs down to when they have to compete with high capacity factor offshore wind, battery firmed utility solar, pumped hydro, etc. in 2040. It'll be a fascinating engineering challenge. I hope they can make it happen, but I doubt it.

The next big problem after hitting positive energy production will be sustainability. My understanding is that the walls of the reactor get hit with enough stray neutrons that they degrade (often in radioactive ways). Unlike in fission reactors where you can put in a lot of absorptive shielding (like lead), in a fusion reactor you have to keep the magnets close to what they are working on.

Note, I am not talking about really long term radioactive waste here, more like things that are dangerous for less than 100 years. Still problematic, but not for millions of years like fission.

Yes and no.

ITER will be first device to produce more heat energy than put in, but it won't be generating any electricity. [1] It will instead be used to make research on, so we can plan the next project, codenamed DEMO.

DEMO will produce net energy, but still be experimental, for designing final version of a commercial fusion power plant. And that commercial plant is aimed to be working by 2050. [2]

ITER is rather looked upon as risk-free and certain way to fusion, whereas startups... are startups. IMHO, we need both approaches.

Also there are many more fusion startups than General Fusion, here are some to follow:

- Tokamak Energy: https://www.youtube.com/channel/UCuSlFJbBUIj1zfJLRnGXSow - LPP Fusion: https://www.youtube.com/channel/UCiBditpj7sdROMYz02qoCMQ - TAE Technologies: https://www.youtube.com/channel/UC-LHpK7z8vjMq2-pt4wG4ug - Commonwealth Fusion Systems: https://cfs.energy - First Light Fusion: https://firstlightfusion.com

1: https://www.iter.org/proj/inafewlines 2: https://www.iter.org/mag/3/22

No. The notion that achieving a certain plasma physics performance means viable fusion has arrived is a very common misconception. It's quite possible that even if the plasma physics problems are well solved, fusion could end up never being viable, for engineering/economic reasons.

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